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Measurements of field output factor by using different detectors in CyberKnifePurpose

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Measurements of field output factor by using different detectors in CyberKnifePurpose: Small field dosimetry is challenging, and the main restrictions of most dosimeters are an inadequate spatial resolution, water nonequivalence, and energy dependency. A methodical studies of different detectors and the field output factors is reported, targeted on illustrative its response in small fields and exploring its suitability for small field reference dosimetry.

Methods: All detectors were calibrated under 60Co irradiation. Different detectors are used to measure output factor and output correction factor is used for each detector by using MC correction data. OF measurements were performed in 6 MV photon beams by a CyberKnife®. A PTW 60019 MicroDiaond, PTW 60018 Silicon diode, PTW31018 MicroLion and Plastic Scintillator Detector (PSD) were used. The field output factor is calculated by using Alfonso formulaADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.3005481”, “ISBN” : “0094-2405 (Print)”, “ISSN” : “00942405”, “PMID” : “19070252”, “abstract” : “The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.”, “author” : { “dropping-particle” : “”, “family” : “Alfonso”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Capote”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huq”, “given” : “M. Saiful”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kju00e4ll”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mackie”, “given” : “T. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ullrich”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vatnitsky”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “11”, “issued” : { “date-parts” : “2008” }, “page” : “5179-5186”, “title” : “A new formalism for reference dosimetry of small and nonstandard fields”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=727fa668-ab3f-4623-82d7-412c8121e6ac” } , “mendeley” : { “formattedCitation” : “<sup>1</sup>”, “plainTextFormattedCitation” : “1”, “previouslyFormattedCitation” : “<sup>1</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }1 then correction factors were applied and we compared the result with each other. Output factors for a CyberKnife system were measured in circular fields with diameters from 5 mm to 60 mm. The measurements were made in a water tank at a 1.5 cm depth and an 80 cm source axis distance.

Results: The results of the current study displayed that; all the detectors agreed with the Monte Carlo values for cones of 20 mm or greater in diameter, for smaller fields (<10 mm), each dosimeter type exhibited different behaviors; The silicon diodes over-responded because of their water nonequivalence; the microLion; and Eradin W1 Scintillator (PSD) was the only detector within the uncertainties of the Monte Carlo simulations for all the cones. The results prove the reproducibility of the MD and MicroLion response and afford a validation of those detectors in small field dosimetry. In principle, accurate reference dosimetry is thus viable by using the microDiamond and MicroLion dosimeter for field sizes down to 5 mm.

Keywords: synthetic diamond, microDiamond, MicroLion, Plastic Scintillator Detector (PSD), small field dosimetry, reference dosimetry.

Introduction
The CyberKnife system offers several advantages over the other devices: it remains a frameless, real-time image-guided, and nonisocentric treatment modality. It comprises of a 6-MV linear accelerator mounted on a robotic manipulator arm that has six degrees of freedom. The CyberKnife system can deliver small fields using 12 circular tungsten cones that are 5 mm – 60 mm in diameter (i.e., 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35,40, 50, and 60 mm). Each radiosurgery treatment apparatus should be modeled into the treatment planning systemADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1016/S0958-3947(98)00013-2”, “ISBN” : “0958-3947”, “ISSN” : “09583947”, “PMID” : “9783268”, “abstract” : “Performing and assuring the quality of the planning and delivery of stereotactic radiosurgery with photon beams requires accurate evaluation of beam parameters, usually including output factors, tissue-phantom ratios and off-axis ratios, and measurement of actual dose distributions from simulated treatments. For the small photon fields used in radiosurgery, these measurements require special equipment and techniques, which are described in this review.”, “author” : { “dropping-particle” : “”, “family” : “Duggan”, “given” : “D. M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Coffey”, “given” : “C. W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Dosimetry”, “id” : “ITEM-1”, “issue” : “3”, “issued” : { “date-parts” : “1998” }, “page” : “153-159”, “title” : “Small photon field dosimetry for stereotactic radiosurgery”, “type” : “article-journal”, “volume” : “23” }, “uris” : “http://www.mendeley.com/documents/?uuid=72319565-5ef0-486b-9553-0807d5e12828” } , “mendeley” : { “formattedCitation” : “<sup>2</sup>”, “plainTextFormattedCitation” : “2”, “previouslyFormattedCitation” : “<sup>2</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }2 because some factors are particular to each accelerator. Francescon et al proved that the constraints that have the highest impact on small-field total scatter factors are the electron spot size and the nominal electron energy incident on the target. A change of ±4% was detected in the total scatter factor of the 5-mm cone with a change of ±0.5 mm on the electron spot size.ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.2828195”, “ISBN” : “00942405 (ISSN)”, “ISSN” : “00942405”, “PMID” : “18383671”, “abstract” : “The scope of this study was to estimate total scatter factors (S(c,p)) of the three smallest collimators of the Cyberknife radiosurgery system (5-10 mm in diameter), combining experimental measurements and Monte Carlo simulation. Two microchambers, a diode, and a diamond detector were used to collect experimental data. The treatment head and the detectors were simulated by means of a Monte Carlo code in order to calculate correction factors for the detectors and to estimate total scatter factors by means of a consistency check between measurement and simulation. Results for the three collimators were: S(c,p) (5 mm) = 0.677 +/- 0.004, S(c,p) (7.5 mm) = 0.820 +/- 0.008, S(c,p) (10 mm) = 0.871 +/- 0.008, all relative to the 60 mm collimator at 80 cm source-to-detector distance. The method also allows the full width at half maximum of the electron beam to be estimated; estimations made with different collimators and different detectors were in excellent agreement and gave a value of 2.1 mm. Correction factors to be applied to the detectors for the measurement of S(c,p) were consistent with a prevalence of volume effect for the microchambers and the diamond and a prevalence of scattering from high-Z material for the diode detector. The proposed method is more sensitive to small variations of the electron beam diameter with respect to the conventional method used to commission Monte Carlo codes, i.e., by comparison with measured percentage depth doses (PDD) and beam profiles. This is especially important for small fields (less than 10 mm diameter), for which measurements of PDD and profiles are strongly affected by the type of detector used. Moreover, this method should allow S(c,p) of Cyberknife systems different from the unit under investigation to be estimated without the need for further Monte Carlo calculation, provided that one of the microchambers or the diode detector of the type used in this study are employed. The results for the diamond are applicable only to the specific detector that was investigated due to excessive variability in manufacturing.”, “author” : { “dropping-particle” : “”, “family” : “Francescon”, “given” : “Paolo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Cora”, “given” : “Stefania”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Cavedon”, “given” : “Carlo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “2008” }, “page” : “504-513”, “title” : “Total scatter factors of small beams: a multidetector and Monte Carlo study.”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=e5052953-fcc1-4317-be50-64d0b8e0310a” } , “mendeley” : { “formattedCitation” : “<sup>3</sup>”, “plainTextFormattedCitation” : “3”, “previouslyFormattedCitation” : “<sup>3</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }3 Moreover, conventional dosimeters often underestimate the dose delivered by small radiation fields because of volume-averaging and perturbation effects.ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.3005481”, “ISBN” : “0094-2405 (Print)”, “ISSN” : “00942405”, “PMID” : “19070252”, “abstract” : “The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.”, “author” : { “dropping-particle” : “”, “family” : “Alfonso”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Capote”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huq”, “given” : “M. Saiful”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kju00e4ll”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mackie”, “given” : “T. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ullrich”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vatnitsky”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “11”, “issued” : { “date-parts” : “2008” }, “page” : “5179-5186”, “title” : “A new formalism for reference dosimetry of small and nonstandard fields”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=727fa668-ab3f-4623-82d7-412c8121e6ac” } , “mendeley” : { “formattedCitation” : “<sup>1</sup>”, “plainTextFormattedCitation” : “1”, “previouslyFormattedCitation” : “<sup>1</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }1,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.1544678”, “ISBN” : “0094-2405 (Print)\r0094-2405”, “ISSN” : “00942405”, “PMID” : “12674234”, “abstract” : “In this study we investigate the effect of detector size in the dosimetry of small fields and steep dose gradients with a particular emphasis on IMRT measurements. Comparisons of calculated and measured cross-profiles and absolute dose values of IMRT treatment plans are presented. As a consequence of the finite size of the detector that was used for the commissioning of the IMRT tool, local discrepancies of more than 10% are found between calculated cross-profiles of intensity modulated beams and intensity modulated profiles measured with film. Absolute dose measurements of intensity modulated fields with a 0.6 cm3 Farmer chamber show significant differences of more than 6% between calculated and measured dose values at the isocenter of an IMRT treatment plan. Differences of not more than 2% are found in the same experiment for dose values measured with a 0.015 cm3 pinpoint ion chamber. A method to correct for the spatial response of finite-sized detectors and to obtain the “real” penumbra width of cross-profiles from measurements is introduced. Output factor measurements are performed with different detectors and are presented as a function of detector size for a 1 x 1 cm2 field. Because of its high spatial resolution and water equivalence, a diamond detector is found to be suitable as an alternative to other detectors used for small field dosimetry as there are photographic and photochromic film, TLDs, or water-equivalent scintillation detectors.”, “author” : { “dropping-particle” : “”, “family” : “Laub”, “given” : “Wolfram U”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Wong”, “given” : “Tony”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “3”, “issued” : { “date-parts” : “2003” }, “page” : “341-347”, “title” : “The volume effect of detectors in the dosimetry of small fields used in IMRT.”, “type” : “article-journal”, “volume” : “30” }, “uris” : “http://www.mendeley.com/documents/?uuid=377222f1-12bc-474a-b0cf-20ed30467d51” } , “mendeley” : { “formattedCitation” : “<sup>4</sup>”, “plainTextFormattedCitation” : “4”, “previouslyFormattedCitation” : “<sup>4</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }4 Spatial resolution is thus an important property when dealing with small fields because no flat dose region exists, resulting in the delivery of a non-uniform dose throughout the detector. The greatest challenge associated with small-field dosimetry is the lateral electronic disequilibrium. Its impact on dosimetry has been broadly described in the literature.ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1016/S0958-3947(98)00013-2”, “ISBN” : “0958-3947”, “ISSN” : “09583947”, “PMID” : “9783268”, “abstract” : “Performing and assuring the quality of the planning and delivery of stereotactic radiosurgery with photon beams requires accurate evaluation of beam parameters, usually including output factors, tissue-phantom ratios and off-axis ratios, and measurement of actual dose distributions from simulated treatments. For the small photon fields used in radiosurgery, these measurements require special equipment and techniques, which are described in this review.”, “author” : { “dropping-particle” : “”, “family” : “Duggan”, “given” : “D. M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Coffey”, “given” : “C. W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Dosimetry”, “id” : “ITEM-1”, “issue” : “3”, “issued” : { “date-parts” : “1998” }, “page” : “153-159”, “title” : “Small photon field dosimetry for stereotactic radiosurgery”, “type” : “article-journal”, “volume” : “23” }, “uris” : “http://www.mendeley.com/documents/?uuid=72319565-5ef0-486b-9553-0807d5e12828” } , “mendeley” : { “formattedCitation” : “<sup>2</sup>”, “plainTextFormattedCitation” : “2”, “previouslyFormattedCitation” : “<sup>2</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }2,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.2219774”, “ISSN” : “00942405”, “author” : { “dropping-particle” : “”, “family” : “Araki”, “given” : “Fujio”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2006”, “7”, “26” }, “page” : “2955-2963”, “publisher” : “American Association of Physicists in Medicine”, “title” : “Monte Carlo study of a Cyberknife stereotactic radiosurgery system”, “type” : “article-journal”, “volume” : “33” }, “uris” : “http://www.mendeley.com/documents/?uuid=02f9cb87-a5a9-34ed-9ac6-9b03279c4c0d” } , “mendeley” : { “formattedCitation” : “<sup>5</sup>”, “plainTextFormattedCitation” : “5”, “previouslyFormattedCitation” : “<sup>5</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }5,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/41/1/008”, “ISBN” : “0031-9155”, “ISSN” : “0031-9155”, “PMID” : “8685261”, “abstract” : “Accurate dosimetry of small-field photon beams used in stereotactic radiosurgery (SRS) can be made difficult because of the presence of lateral electronic disequilibrium and steep dose gradients. In the published literature, data acquisition for radiosurgery is mainly based on diode and film dosimetry, and sometimes on small ionization chamber or thermolominescence dosimetry. These techniques generally do not provide the required precision because of their energy dependence and/or poor resolution. In this work PTW diamond detectors and Monte Carlo (EGS4) techniques have been added to the above tools to measure and calculate SRS treatment planning requirements. The validity of the EGS4 generated data has been confirmed by comparing results to those obtained with an ionization chamber, where the field size is large enough for electronic equilibrium to be established at the central axis. Using EGS4 calculations, the beam characteristics under the experimental conditions have also been quantified. It was shown that diamond detectors are potentially ideal for SRS and yield more accurate results than the above traditional modes of dosimetry.”, “author” : { “dropping-particle” : “”, “family” : “Heydarian”, “given” : “M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hoban”, “given” : “P. W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Beddoe”, “given” : “a. H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “1996” }, “page” : “93-110”, “title” : “A comparison of dosimetry techniques in stereotactic radiosurgery.”, “type” : “article-journal”, “volume” : “41” }, “uris” : “http://www.mendeley.com/documents/?uuid=1990e90a-1582-4107-aec3-30d09ea7177c” } , “mendeley” : { “formattedCitation” : “<sup>6</sup>”, “plainTextFormattedCitation” : “6”, “previouslyFormattedCitation” : “<sup>6</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }6,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/47/11/401”, “ISBN” : “0031-9155”, “ISSN” : “00319155”, “PMID” : “12108781”, “abstract” : “The purpose of this study was to investigate beam output factors (OFs) for conformal radiation therapy and to compare the OFs measured with different detectors with those simulated with Monte Carlo methods. Four different detectors (diode, diamond, pinpoint and ionization chamber) were used to measure photon beam OFs in a water phantom at a depth of 10 cm with a sourceu2013surface distance (SSD) of 100 cm. Square fields with widths ranging from 1 cm to 15 cm were observed; the OF for the different field sizes was normalized to that measured at a 5 cm u00d7 5cm fieldsize at a depth of10cm. TheBEAM/EGS4 programwas used to simulate the exact geometry of a 6MV photon beam generated by the linear accelerator, and the DOSXYZ-code was implemented to calculate the OFs for all field sizes. Two resolutions (0.1 cm and 0.5 cm voxel size) were chosen here. In addition, to model the detector four kinds of material, water, air, graphite or silicon, were placed in the corresponding voxels. Profiles and depth dose distributions resulting from the simulation show good agreement with the measurements. Deviations of less than 2% can be observed. TheOFmeasured with different detectors inwater vary by more than 35% for 1 cm u00d7 1 cm fields. This result can also be found for the simulated OF with different voxel sizes and materials. For field sizes of at least 2 cm u00d7 2 cm the deviations between all measurements and simulations are below 3%. This demonstrates that very small fields have a bad effect on dosimetric accuracy and precision. Finally, Monte Carlo methods can be significant in determining the OF for small fields.”, “author” : { “dropping-particle” : “”, “family” : “Haryanto”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fippel”, “given” : “M”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Laub”, “given” : “W”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Dohm”, “given” : “O”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Nu00fcsslin”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in Medicine and Biology”, “id” : “ITEM-1”, “issued” : { “date-parts” : “2002” }, “page” : “N133-43”, “title” : “Investigation of photon beam output factors for conformal radiation therapy u2014 Monte Carlo simulations and measurements”, “type” : “article-journal”, “volume” : “47” }, “uris” : “http://www.mendeley.com/documents/?uuid=f933b8b9-665c-4623-8135-ab0cc3d152c2” } , “mendeley” : { “formattedCitation” : “<sup>7</sup>”, “plainTextFormattedCitation” : “7”, “previouslyFormattedCitation” : “<sup>7</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }7. Current stereotactic radiotherapy techniques depend on the enhancements achieved in the treatment of cancer disease by a better spatial localization of high dose irradiation volumes. This, in turn, implies that an excessive effort is to be done to the enlargement of protocols and specific detectors for small field dosimetry.ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.3005481”, “ISBN” : “0094-2405 (Print)”, “ISSN” : “00942405”, “PMID” : “19070252”, “abstract” : “The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.”, “author” : { “dropping-particle” : “”, “family” : “Alfonso”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Capote”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huq”, “given” : “M. 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R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ullrich”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vatnitsky”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “11”, “issued” : { “date-parts” : “2008” }, “page” : “5179-5186”, “title” : “A new formalism for reference dosimetry of small and nonstandard fields”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=727fa668-ab3f-4623-82d7-412c8121e6ac” } , “mendeley” : { “formattedCitation” : “<sup>1</sup>”, “plainTextFormattedCitation” : “1”, “previouslyFormattedCitation” : “<sup>1</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }1,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.2815356”, “ISBN” : “00942405 (ISSN)”, “ISSN” : “00942405”, “PMID” : “18293576”, “abstract” : “Advances in radiation treatment with beamlet-based intensity modulation, image-guided radiation therapy, and stereotactic radiosurgery (including specialized equipments like CyberKnife, Gamma Knife, tomotherapy, and high-resolution multileaf collimating systems) have resulted in the use of reduced treatment fields to a subcentimeter scale. Compared to the traditional radiotherapy with fields u2265 4 u00d7 4 u2002 cm 2 , this can result in significant uncertainty in the accuracy of clinical dosimetry. The dosimetry of small fields is challenging due to nonequilibrium conditions created as a consequence of the secondary electron track lengths and the source size projected through the collimating system that are comparable to the treatmentfield size. It is further complicated by the prolonged electron tracks in the presence of low-density inhomogeneities. Also, radiation detectors introduced into such fields usually perturb the level of disequilibrium. Hence, the dosimetric accuracy previously achieved for standard radiotherapy applications is at risk for both absolute and relative dose determination. This article summarizes the present knowledge and gives an insight into the future procedures to handle the nonequilibrium radiationdosimetry problems. It is anticipated that new miniature detectors with controlled perturbations and corrections will be available to meet the demand for accurate measurements. It is also expected that the Monte Carlo techniques will increasingly be used in assessing the accuracy, verification, and calculation of dose, and will aid perturbation calculations of detectors used in small and highly conformal radiation beams.”, “author” : { “dropping-particle” : “”, “family” : “Das”, “given” : “Indra J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ding”, “given” : “George X.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ahnesju00f6”, “given” : “Anders”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “2007” }, “page” : “206-215”, “title” : “Small fields: Nonequilibrium radiation dosimetry”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=12222712-0305-4b48-8b5c-e8e7396ee1ec” } , “mendeley” : { “formattedCitation” : “<sup>8</sup>”, “plainTextFormattedCitation” : “8”, “previouslyFormattedCitation” : “<sup>8</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }8,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1063/1.4954111”, “author” : { “dropping-particle” : “”, “family” : “Das”, “given” : “Indra J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Morales”, “given” : “Johnny”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Francescon”, “given” : “Paolo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “id” : “ITEM-1”, “issue” : “June”, “issued” : { “date-parts” : “2016” }, “title” : “Small field dosimetry : What have we learnt ? Small Field Dosimetry : What Have We Learnt ?”, “type” : “article-journal”, “volume” : “398” }, “uris” : “http://www.mendeley.com/documents/?uuid=4d0d569e-3e0b-46a1-baf8-e35ba963b32a” } , “mendeley” : { “formattedCitation” : “<sup>9</sup>”, “plainTextFormattedCitation” : “9”, “previouslyFormattedCitation” : “<sup>9</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }9,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/54/9/024”, “ISBN” : “0031-9155”, “ISSN” : “0031-9155”, “PMID” : “19384005”, “abstract” : “The purpose of this study was the investigation of perturbation factors for microionization chambers in small field dosimetry and the influence of penumbra for different spot sizes. To this purpose, correlated sampling was implemented in the EGSnrc Monte Carlo (MC) user code cavity: CScavity. CScavity was first benchmarked against results in the literature for an NE2571 chamber. An efficiency increase of 17 was attained for the calculation of a realistic chamber perturbation factor in a water phantom. Calculations have been performed for microionization chambers of type PinPoint 31006 and PinPoint 31016 in full BEAMnrc linac simulations. Investigating the physical backgrounds of the differences for these small field settings, perturbation factors have been split up into (1) central electrode perturbation, (2) wall perturbation, (3) air-to-water perturbation (chamber volume air-to-water) and (4) water volume perturbation (water chamber volume to 1 mm(3) voxel). The influence of different spot sizes, position in penumbra, measuring depth and detector geometry on these perturbation factors has been investigated, in a 0.8 x 0.8 cm(2) field setting. p(cel) for the PP31006 steel electrode shows a variation of up to 1% in the lateral position, but only 0.4% for the PP31016 with an Al electrode. The air-to-water perturbation in the optimal scanning direction for both profiles and depth is most influenced by the radiation field, and only to a small extent the chamber geometry. The PP31016 geometry (shorter, larger radius) requires less total perturbation within the central axis of the field, but results in slightly larger variations off axis in the optimal scanning direction. Smaller spot sizes (0.6 mm FWHM) and sharper penumbras, compared to larger spot sizes (2 mm FWHM), result in larger perturbation starting in the penumbra. The longer geometries of the PP31006/14/15 exhibit in the non-optimal scanning direction large variations in total perturbation (p(tot) 1.201(4) (0.6 mm spot, 3 mm off axis, type A MC uncertainty) to 0.803(4) (5 mm off axis)) mainly due to volume perturbation. Therefore in IMRT settings, when the detector is not always in the optimal scanning direction, the PP31016 geometry requires less extreme perturbation (max p(tot) 1.130(3)) and shows less variation. However, these results suggest that small variations in positioning, spot size or MLC result in large differences in perturbation factors. Therefore even these 0.016 cm(3) ionization chau2026”, “author” : { “dropping-particle” : “”, “family” : “Crop”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Reynaert”, “given” : “N”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Pittomvils”, “given” : “G”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Paelinck”, “given” : “L”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Wagter”, “given” : “C”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vakaet”, “given” : “L”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Thierens”, “given” : “H”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “9”, “issued” : { “date-parts” : “2009” }, “page” : “2951-69”, “title” : “The influence of small field sizes, penumbra, spot size and measurement depth on perturbation factors for microionization chambers.”, “type” : “article-journal”, “volume” : “54” }, “uris” : “http://www.mendeley.com/documents/?uuid=3910b988-1890-42eb-a9ae-22501f62194c” } , “mendeley” : { “formattedCitation” : “<sup>10</sup>”, “plainTextFormattedCitation” : “10”, “previouslyFormattedCitation” : “<sup>10</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }10,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “author” : { “dropping-particle” : “”, “family” : “Aspradakis”, “given” : “M.M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Byrne”, “given” : “J.P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Duane”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Conway”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Warrington”, “given” : “A.P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “id” : “ITEM-1”, “issued” : { “date-parts” : “2010” }, “title” : “IPEM report 103: Small field MV photon dosimetry”, “type” : “article” }, “uris” : “http://www.mendeley.com/documents/?uuid=e66a143e-4ba4-341e-8e68-a566b2c88c16” } , “mendeley” : { “formattedCitation” : “<sup>11</sup>”, “plainTextFormattedCitation” : “11”, “previouslyFormattedCitation” : “<sup>11</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }11,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4812687”, “ISBN” : “0094-2405”, “ISSN” : “0094-2405”, “PMID” : “23927339”, “abstract” : “PURPOSE: The Alfonso et al. Med. Phys. 35, 5179-5186 (2008) formalism for small field dosimetry proposes a set of correction factors (kQclin,Qmsrfclin,fmsr) which account for differences between the detector response in nonstandard (clinical) and machine-specific-reference fields. In this study, the Monte Carlo method was used to investigate the viability of such small field correction factors for four different detectors irradiated under a variety of conditions. Because kQclin,Qmsrfclin,fmsr values for single detector position measurements are influenced by several factors, a new theoretical formalism for integrated-detector-position dose area product (DAP) measurements is also presented and was tested using Monte Carlo simulations.\n\nMETHODS: A BEAMnrc linac model was built and validated for a Varian Clinac iX accelerator. Using the egs++ geometry package, detailed virtual models were built for four different detectors: a PTW 60012 unshielded diode, a PTW 60003 Diamond detector, a PTW 31006 PinPoint (ionization chamber), and a PTW 31018 MicroLion (liquid-filled ionization chamber). The egs_chamber code was used to investigate the variation of kQclin,Qmsrfclin,fmsr with detector type, detector construction, field size, off-axis position, and the azimuthal angle between the detector and beam axis. Simulations were also used to consider the DAP obtained by each detector: virtual detectors and water voxels were scanned through high resolution grids of positions extending far beyond the boundaries of the fields under consideration.\n\nRESULTS: For each detector, the correction factor (kQclin,Qmsrfclin,fmsr) was shown to depend strongly on detector off-axis position and detector azimuthal angle in addition to field size. In line with previous studies, substantial interdetector variation was also observed. However, it was demonstrated that by considering DAPs rather than single-detector-position dose measurements the high level of interdetector variation could be eliminated. Under small field conditions, mass density was found to be the principal determinant of water equivalence. Additionally, the mass densities of components outside the sensitive volumes were found to influence the detector response.\n\nCONCLUSIONS: kQclin,Qmsrfclin,fmsr values for existing detector designs depend on a host of variables and their calculation typically relies on the use of time-intensive Monte Carlo methods. Future moves toward density-compensated detector designs or DAu2026”, “author” : { “dropping-particle” : “”, “family” : “Underwood”, “given” : “T S a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Winter”, “given” : “H C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hill”, “given” : “M a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fenwick”, “given” : “J D”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Carlo”, “given” : “Monte”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Underwood”, “given” : “T S a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Winter”, “given” : “H C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hill”, “given” : “M a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fenwick”, “given” : “J D”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2013” }, “page” : “082102”, “title” : “Detector density and small field dosimetry: integral versus point dose measurement schemes.”, “type” : “article-journal”, “volume” : “40” }, “uris” : “http://www.mendeley.com/documents/?uuid=4a0731b1-a214-4d4d-b21e-4f98c35211e0” } , “mendeley” : { “formattedCitation” : “<sup>12</sup>”, “plainTextFormattedCitation” : “12”, “previouslyFormattedCitation” : “<sup>12</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }12,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4930053”, “ISBN” : “0094-2405 (Print) 0094-2405 (Linking)”, “ISSN” : “0094-2405”, “PMID” : “26429279”, “abstract” : “Articles you may be interested in Detector dose response in megavoltage small photon beams. I. Theoretical concepts Med. Phys. 42, 6033 (2015); 10.1118/1.4930053 Development and characterization of a three-dimensional radiochromic film stack dosimeter for megavoltage photon beam dosimetry Med. Phys. 41, 052104 (2014); 10.1118/1.4871781 Projection imaging of photon beams by the u010cerenkov effect Med. Phys. 40, 012101 (2013); 10.1118/1.4770286 Dose response of BaFBrI : Eu 2 + storage phosphor plates exposed to megavoltage photon beams Med. Phys. 34, 103 (2007); 10.1118/1.2400617 Absorbed dose conversion factors for therapeutic kilovoltage and megavoltage x-ray beams calculated by the Monte Carlo method Purpose: To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. Methods: In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano’s theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of pertur-bation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components. Results: Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes. Conclusions: Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine criticu2026”, “author” : { “dropping-particle” : “”, “family” : “Bouchard”, “given” : “Hugo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “Jan”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Duane”, “given” : “Simon”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kamio”, “given” : “Yuji”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “Hugo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “10”, “issued” : { “date-parts” : “2015” }, “page” : “6033-6047”, “title” : “Detector dose response in megavoltage small photon beams. I. Theoretical concepts”, “type” : “article-journal”, “volume” : “42” }, “uris” : “http://www.mendeley.com/documents/?uuid=7083b1ce-12ac-4477-988f-03e74890ed01” } , “mendeley” : { “formattedCitation” : “;sup;13;/sup;”, “plainTextFormattedCitation” : “13”, “previouslyFormattedCitation” : “;sup;13;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }13,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1007/s13246-015-0334-9”, “ISBN” : “1879-5447 (Electronic)\r0158-9938 (Linking)”, “ISSN” : “18795447”, “PMID” : “25744538”, “abstract” : “There have been substantial advances in small field dosimetry techniques and technologies, over the last decade, which have dramatically improved the achievable accuracy of small field dose measurements. This educational note aims to help radiation oncology medical physicists to apply some of these advances in clinical practice. The evaluation of a set of small field output factors (total scatter factors) is used to exemplify a detailed measurement and simulation procedure and as a basis for discussing the possible effects of simplifying that procedure. Field output factors were measured with an unshielded diode and a micro-ionisation chamber, at the centre of a set of square fields defined by a micro-multileaf collimator. Nominal field sizes investigated ranged from 6 x 6 to 98 x 98 mm(2). Diode measurements in fields smaller than 30 mm across were corrected using response factors calculated using Monte Carlo simulations of the diode geometry and daisy-chained to match micro-chamber measurements at intermediate field sizes. Diode measurements in fields smaller than 15 mm across were repeated twelve times over three separate measurement sessions, to evaluate the reproducibility of the radiation field size and its correspondence with the nominal field size. The five readings that contributed to each measurement on each day varied by up to 0.26 %, for the “very small” fields smaller than 15 mm, and 0.18 % for the fields larger than 15 mm. The diode response factors calculated for the unshielded diode agreed with previously published results, within uncertainties. The measured dimensions of the very small fields differed by up to 0.3 mm, across the different measurement sessions, contributing an uncertainty of up to 1.2 % to the very small field output factors. The overall uncertainties in the field output factors were 1.8 % for the very small fields and 1.1 % for the fields larger than 15 mm across. Recommended steps for acquiring small field output factor measurements for use in radiotherapy treatment planning system beam configuration data are provided.”, “author” : { “dropping-particle” : “”, “family” : “Kairn”, “given” : “T.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Charles”, “given” : “P. H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Cranmer-Sargison”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Crowe”, “given” : “S. B.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Langton”, “given” : “C. M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Thwaites”, “given” : “D. I.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “V.”, “family” : “Trapp”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Australasian Physical and Engineering Sciences in Medicine”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “2015” }, “page” : “357-367”, “title” : “Clinical use of diodes and micro-chambers to obtain accurate small field output factor measurements”, “type” : “article-journal”, “volume” : “38” }, “uris” : “http://www.mendeley.com/documents/?uuid=83eaf8dd-2a37-495b-b814-a40ba757f0f1” } , “mendeley” : { “formattedCitation” : “;sup;14;/sup;”, “plainTextFormattedCitation” : “14”, “previouslyFormattedCitation” : “;sup;14;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }14,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “author” : { “dropping-particle” : “”, “family” : “Veselsky”, “given” : “T”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Jr”, “given” : “J Novotny”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Pastykova”, “given” : “V”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Pipek”, “given” : “J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “id” : “ITEM-1”, “issued” : { “date-parts” : “0” }, “page” : “60019”, “title” : “Assessment of MicroDiamond PTW 60019 detector and its use in small radiosurgery fields of Leksell Gamma Knife”, “type” : “article-journal” }, “uris” : “http://www.mendeley.com/documents/?uuid=f43fcf46-4ceb-462e-bc08-b48eac43dbe2” } , “mendeley” : { “formattedCitation” : “;sup;15;/sup;”, “plainTextFormattedCitation” : “15”, “previouslyFormattedCitation” : “;sup;15;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }15 Definitely, many papers have been recently published pointing at characterizing commercial dosimeters in these challenging conditions. Their response was examined under irradiation in field sizes down to 5 mm and Monte Carlo (MC) simulations were accomplished in order to calculate the correction factors to be applied to the obtained investigational data.

The recently commercialized PTW microDiamond (MD) ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4729739”, “ISBN” : “00942405 (ISSN)”, “ISSN” : “00942405”, “PMID” : “22830781”, “abstract” : “PURPOSE: To determine the potentialities of synthetic single crystal diamond Schottky diodes for accurate dose measurements in radiation therapy small photon beams.\n\nMETHODS: The dosimetric properties of a diamond-based detector were assessed by comparison with a reference microionization chamber. The diamond device was operated at zero bias voltage under irradiation with high-energy radiotherapic photon beams. The stability of the detector response and its dose and dose rate dependence were measured. Different square field sizes ranging from 1 u00d7 1 cm(2) to 10 u00d7 10 cm(2) were used during comparative dose distribution measurements by means of percentage depth dose curves (PDDs), lateral beam profiles, and output factors. The angular and temperature dependence of the diamond detector response were also studied.\n\nRESULTS: The detector response shows a deviation from linearity of less than u00b10.5% in the 0.01-7 Gy range and dose rate dependence below u00b10.5% in the 1-6 Gyu2215min range. PDDs and output factors are in good agreement with those measured by the reference ionization chamber within 1%. No angular dependence is observed by rotating the detector along its axis, while u223c3.5% maximum difference is measured by varying the radiation incidence angle in the polar direction. The temperature dependence was investigated as well and a u00b10.2% variation of the detector response is found in the 18-40 u00b0C range.\n\nCONCLUSIONS: The obtained results indicate the investigated synthetic diamond-based detector as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.”, “author” : { “dropping-particle” : “”, “family” : “Ciancaglioni”, “given” : “I.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Milani”, “given” : “E.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Prestopino”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona”, “given” : “C.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Consorti”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Petrucci”, “given” : “a.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Notaristefani”, “given” : “F.”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “7”, “issued” : { “date-parts” : “2012” }, “page” : “4493”, “title” : “Dosimetric characterization of a synthetic single crystal diamond detector in clinical radiation therapy small photon beams”, “type” : “article-journal”, “volume” : “39” }, “uris” : “http://www.mendeley.com/documents/?uuid=a5288c2b-212d-4603-8593-50d88db599d0” } , “mendeley” : { “formattedCitation” : “;sup;16;/sup;”, “plainTextFormattedCitation” : “16”, “previouslyFormattedCitation” : “;sup;16;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }16,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4961402”, “ISSN” : “0094-2405”, “author” : { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Prestopino”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona”, “given” : “C.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “9”, “issued” : { “date-parts” : “2016” }, “page” : “5205-5212”, “title” : “Experimental determination of the PTW 60019 microDiamond dosimeter active area and volume”, “type” : “article-journal”, “volume” : “43” }, “uris” : “http://www.mendeley.com/documents/?uuid=f2b017e8-8cc7-4923-b3b8-086a62354498” } , “mendeley” : { “formattedCitation” : “;sup;17;/sup;”, “plainTextFormattedCitation” : “17”, “previouslyFormattedCitation” : “;sup;17;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }17, were among the most studied detectorsADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.2734383”, “ISBN” : “0094-2405 (Print)\n0094-2405 (Linking)”, “ISSN” : “00942405”, “PMID” : “17654901”, “abstract” : “A variety of detectors and procedures for the measurement of small field output factors are discussed in the current literature. Different detectors with or without corrections are recommended. Correction factors are often derived by Monte Carlo methods, where the bias due to approximations in the model is difficult to judge. Over that, results appear to be contradictory in some cases. In this work, output factors were measured for field sizes from 4 mm up to 180 mm side length with different detectors. A simple linear correction for the energy response of solid state detectors is proposed. This led to identical values down to 8 mm field size, as long as the size of the detector is small against the field size. The correction was of the order of a few percent. For a shielded silicon diode it was well below 1%. A physically meaningful function is proposed in order to calculate output factors for arbitrary field sizes with high accuracy.”, “author” : { “dropping-particle” : “”, “family” : “Sauer”, “given” : “Otto A”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Wilbert”, “given” : “Ju00fcrgen”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “6”, “issued” : { “date-parts” : “2007” }, “page” : “1983-1988”, “title” : “Measurement of output factors for small photon beams”, “type” : “article-journal”, “volume” : “34” }, “uris” : “http://www.mendeley.com/documents/?uuid=5cb374f3-82f8-4581-8e0a-6928471793ff” } , “mendeley” : { “formattedCitation” : “;sup;18;/sup;”, “plainTextFormattedCitation” : “18”, “previouslyFormattedCitation” : “;sup;18;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }18,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/55/24/002”, “ISBN” : “0031-9155”, “ISSN” : “1361-6560”, “PMID” : “21098913”, “abstract” : “The dosimetry of small fields is important for the use of high resolution photon radiotherapy. Silicon diodes yield a high signal from a small detecting volume which makes them suitable for use in small fields and high dose gradients. Unshielded diodes used in large fields are known to give a varying dose response depending on the proportion of low energy scattered photons in the field. Response variations in small fields can be caused by both spectral variations, and disturbances of the local level of lateral electron equilibrium. We present a model that includes the effects from lack of charged particle equilibrium. The local spectra are calculated by use of fluence pencil kernels and divided into a low and a high energy component. The low energy part is treated with large cavity theory and the high energy part with the Spencer-Attix small cavity theory. Monte Carlo-derived correction factors are used to account for both the local level of electron equilibrium in the field, and deviations from this level in the silicon disk cavity. Results for field sizes ranging from 0.5 u00d7 0.5 to 20 u00d7 20 cmu00b2 are compared to data from full Monte Carlo simulations and measurements. The achieved dose response accuracy is for the smallest fields 1-2%, and for larger fields 0.5%. Spectral variations were of little importance for the small field response, implying that volume averaging, and to some extent interface transient effects, are of importance for use of unshielded diodes in non-equilibrium conditions. The results indicate that diodes should preferably be designed to have the thin layer of active volume padded in between inactive layers of the silicon base material.”, “author” : { “dropping-particle” : “”, “family” : “Eklund”, “given” : “Karin”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ahnesju00f6”, “given” : “Anders”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “24”, “issued” : { “date-parts” : “2010” }, “page” : “7411-23”, “title” : “Modeling silicon diode dose response factors for small photon fields.”, “type” : “article-journal”, “volume” : “55” }, “uris” : “http://www.mendeley.com/documents/?uuid=848478d7-531b-4cb9-877f-23afb79b068b” } , “mendeley” : { “formattedCitation” : “;sup;19;/sup;”, “plainTextFormattedCitation” : “19”, “previouslyFormattedCitation” : “;sup;19;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }19,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/58/8/2431”, “ISBN” : “1361-6560”, “ISSN” : “1361-6560”, “PMID” : “23514734”, “abstract” : “The application of small photon fields in modern radiotherapy requires the determination of total scatter factors Scp or field factors u03a9(f(clin), f(msr))(Q(clin), Q(msr)) with high precision. Both quantities require the knowledge of the field-size-dependent and detector-dependent correction factor k(f(clin), f(msr))(Q(clin), Q(msr)). The aim of this study is the determination of the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)) for different types of detectors in a clinical 6 MV photon beam of a Siemens KD linear accelerator. The EGSnrc Monte Carlo code was used to calculate the dose to water and the dose to different detectors to determine the field factor as well as the mentioned correction factor for different small square field sizes. Besides this, the mean water to air stopping power ratio as well as the ratio of the mean energy absorption coefficients for the relevant materials was calculated for different small field sizes. As the beam source, a Monte Carlo based model of a Siemens KD linear accelerator was used. The results show that in the case of ionization chambers the detector volume has the largest impact on the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)); this perturbation may contribute up to 50% to the correction factor. Field-dependent changes in stopping-power ratios are negligible. The magnitude of k(f(clin), f(msr))(Q(clin), Q(msr)) is of the order of 1.2 at a field size of 1 u00d7 1 cm(2) for the large volume ion chamber PTW31010 and is still in the range of 1.05-1.07 for the PinPoint chambers PTW31014 and PTW31016. For the diode detectors included in this study (PTW60016, PTW 60017), the correction factor deviates no more than 2% from unity in field sizes between 10 u00d7 10 and 1 u00d7 1 cm(2), but below this field size there is a steep decrease of k(f(clin), f(msr))(Q(clin), Q(msr)) below unity, i.e. a strong overestimation of dose. Besides the field size and detector dependence, the results reveal a clear dependence of the correction factor on the accelerator geometry for field sizes below 1 u00d7 1 cm(2), i.e. on the beam spot size of the primary electrons hitting the target. This effect is especially pronounced for the ionization chambers. In conclusion, comparing all detectors, the unshielded diode PTW60017 is highly recommended for small field dosimetry, since its correction factor k(f(clin), f(msr))(Q(clin), Q(msr)) is closest to unity in small fields and mainly independent of the electron beam spot size.”, “author” : { “dropping-particle” : “”, “family” : “Czarnecki”, “given” : “D”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Zink”, “given” : “K”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2013” }, “page” : “2431-44”, “title” : “Monte Carlo calculated correction factors for diodes and ion chambers in small photon fields.”, “type” : “article-journal”, “volume” : “58” }, “uris” : “http://www.mendeley.com/documents/?uuid=44975fa7-24a4-4eac-8310-c66cd36eadd5” } , “mendeley” : { “formattedCitation” : “;sup;20;/sup;”, “plainTextFormattedCitation” : “20”, “previouslyFormattedCitation” : “;sup;20;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }20,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4883795”, “ISSN” : “0094-2405”, “PMID” : “24989398”, “abstract” : “PURPOSE: The aim of the present study is to provide a comprehensive set of detector specific correction factors for beam output measurements for small beams, for a wide range of real time and passive detectors. The detector specific correction factors determined in this study may be potentially useful as a reference data set for small beam dosimetry measurements.\n\nMETHODS: Dose response of passive and real time detectors was investigated for small field sizes shaped with a micromultileaf collimator ranging from 0.6 u00d7 0.6 cm(2) to 4.2 u00d7 4.2 cm(2) and the measurements were extended to larger fields of up to 10 u00d7 10 cm(2). Measurements were performed at 5 cm depth, in a 6 MV photon beam. Detectors used included alanine, thermoluminescent dosimeters (TLDs), stereotactic diode, electron diode, photon diode, radiophotoluminescent dosimeters (RPLDs), radioluminescence detector based on carbon-doped aluminium oxide (Al2O3:C), organic plastic scintillators, diamond detectors, liquid filled ion chamber, and a range of small volume air filled ionization chambers (volumes ranging from 0.002 cm(3) to 0.3 cm(3)). All detector measurements were corrected for volume averaging effect and compared with dose ratios determined from alanine to derive a detector correction factors that account for beam perturbation related to nonwater equivalence of the detector materials.\n\nRESULTS: For the detectors used in this study, volume averaging corrections ranged from unity for the smallest detectors such as the diodes, 1.148 for the 0.14 cm(3) air filled ionization chamber and were as high as 1.924 for the 0.3 cm(3) ionization chamber. After applying volume averaging corrections, the detector readings were consistent among themselves and with alanine measurements for several small detectors but they differed for larger detectors, in particular for some small ionization chambers with volumes larger than 0.1 cm(3).\n\nCONCLUSIONS: The results demonstrate how important it is for the appropriate corrections to be applied to give consistent and accurate measurements for a range of detectors in small beam geometry. The results further demonstrate that depending on the choice of detectors, there is a potential for large errors when effects such as volume averaging, perturbation and differences in material properties of detectors are not taken into account. As the commissioning of small fields for clinical treatment has to rely on accurate dose measurements, the authors recommend the uu2026”, “author” : { “dropping-particle” : “”, “family” : “Azangwe”, “given” : “Godfrey”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Grochowska”, “given” : “Paulina”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Georg”, “given” : “Dietmar”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Izewska”, “given” : “Joanna”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hopfgartner”, “given” : “Johannes”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Lechner”, “given” : “Wolfgang”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andersen”, “given” : “Claus E”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Beierholm”, “given” : “Anders R”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Helt-Hansen”, “given” : “Jakob”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mizuno”, “given” : “Hideyuki”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fukumura”, “given” : “Akifumi”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Yajima”, “given” : “Kaori”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Gouldstone”, “given” : “Clare”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Sharpe”, “given” : “Peter”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Meghzifene”, “given” : “Ahmed”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “Hugo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “7”, “issued” : { “date-parts” : “2014” }, “page” : “072103”, “title” : “Detector to detector corrections: A comprehensive experimental study of detector specific correction factors for beam output measurements for small radiotherapy beams.”, “type” : “article-journal”, “volume” : “41” }, “uris” : “http://www.mendeley.com/documents/?uuid=bea86187-bdda-442b-81de-d101b3277e3c” } , “mendeley” : { “formattedCitation” : “;sup;21;/sup;”, “plainTextFormattedCitation” : “21”, “previouslyFormattedCitation” : “;sup;21;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }21,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4868695”, “ISBN” : “doi:10.1118/1.4868695”, “ISSN” : “0094-2405”, “PMID” : “24694131”, “abstract” : “PURPOSE: To determine detector-specific output correction factors,Formula: see text, in 6 MV small photon beams for air and liquid ionization chambers, silicon diodes, and diamond detectors from two manufacturers.\n\nMETHODS: Field output factors, defined according to the international formalism published byAlfonso et al. Med. Phys. 35, 5179-5186 (2008), relate the dosimetry of small photon beams to that of the machine-specific reference field; they include a correction to measured ratios of detector readings, conventionally used as output factors in broad beams. Output correction factors were calculated with the PENELOPE Monte Carlo (MC) system with a statistical uncertainty (type-A) of 0.15% or lower. The geometries of the detectors were coded using blueprints provided by the manufacturers, and phase-space files for field sizes between 0.5 u00d7 0.5 cm(2) and 10 u00d7 10 cm(2) from a Varian Clinac iX 6 MV linac used as sources. The output correction factors were determined scoring the absorbed dose within a detector and to a small water volume in the absence of the detector, both at a depth of 10 cm, for each small field and for the reference beam of 10 u00d7 10 cm(2).\n\nRESULTS: The Monte Carlo calculated output correction factors for the liquid ionization chamber and the diamond detector were within about u00b1 1% of unity even for the smallest field sizes. Corrections were found to be significant for small air ionization chambers due to their cavity dimensions, as expected. The correction factors for silicon diodes varied with the detector type (shielded or unshielded), confirming the findings by other authors; different corrections for the detectors from the two manufacturers were obtained. The differences in the calculated factors for the various detectors were analyzed thoroughly and whenever possible the results were compared to published data, often calculated for different accelerators and using the EGSnrc MC system. The differences were used to estimate a type-B uncertainty for the correction factors. Together with the type-A uncertainty from the Monte Carlo calculations, an estimation of the combined standard uncertainty was made, assigned to the mean correction factors from various estimates.\n\nCONCLUSIONS: The present work provides a consistent and specific set of data for the output correction factors of a broad set of detectors in a Varian Clinac iX 6 MV accelerator and contributes to improving the understanding of the physics of small photon beau2026”, “author” : { “dropping-particle” : “”, “family” : “Benmakhlouf”, “given” : “Hamza”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Sempau”, “given” : “Josep”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “Pedro”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “4”, “issued” : { “date-parts” : “2014” }, “page” : “041711”, “title” : “Output correction factors for nine small field detectors in 6 MV radiation therapy photon beams: a PENELOPE Monte Carlo study.”, “type” : “article-journal”, “volume” : “41” }, “uris” : “http://www.mendeley.com/documents/?uuid=1641889b-5cce-4c19-922d-32522143645b” } , “mendeley” : { “formattedCitation” : “;sup;22;/sup;”, “plainTextFormattedCitation” : “22”, “previouslyFormattedCitation” : “;sup;22;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }22,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/6/N11”, “ISBN” : “1361-6560 (Electronic)\r0031-9155 (Linking)”, “ISSN” : “1361-6560”, “PMID” : “24594929”, “abstract” : “A previous study of the corrections needed for output factor measurements with the CyberKnife system has been extended to include new diode detectors (IBA SFD and Exradin D1V), an air filled microchamber (Exradin CC01) and a scintillation detector (Exradin W1). The dependence of the corrections on detector orientation (detector long axis parallel versus perpendicular to the beam axis) and source to detector distance (SDD) was evaluated for these new detectors and for those in our previous study. The new diodes are found to over-respond at the smallest (5 mm) field size by 2.5% (D1V) and 3.3% (SFD) at 800 mm SDD, while the CC01 under-responds by 7.4% at the same distance when oriented parallel to the beam. Corrections for all detectors tend to unity as field size increases. The W1 corrections are ;0.5% at all field sizes. Microchamber correction factors increase substantially if the detector is oriented perpendicular to the beam (by up to 23% for the PTW 31014). Corrections also vary with SDD, with the largest variations seen for microchambers in the perpendicular orientation (up to 13% change at 650 mm SDD versus 800 mm) and smallest for diodes (~1% change at 650 mm versus 800 mm). The smallest and most stable corrections are found for diodes, liquid filled microchambers and scintillation detectors, therefore these should be preferred for small field output factor measurements. If air filled microchambers are used, then the parallel orientation should be preferred to the perpendicular, and care should be taken to use corrections appropriate to the measurement SDD.”, “author” : { “dropping-particle” : “”, “family” : “Francescon”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Satariano”, “given” : “N”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “6”, “issued” : { “date-parts” : “2014” }, “page” : “N11-7”, “title” : “Monte Carlo simulated correction factors for output factor measurement with the CyberKnife system-results for new detectors and correction factor dependence on measurement distance and detector orientation.”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=e4342840-5659-4fa3-93f7-dd3fa78a80bc” } , “mendeley” : { “formattedCitation” : “;sup;23;/sup;”, “plainTextFormattedCitation” : “23”, “previouslyFormattedCitation” : “;sup;23;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }23,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4881098”, “ISSN” : “0094-2405”, “PMID” : “24989371”, “abstract” : “PURPOSE: In a previous work, output ratio (ORdet) measurements were performed for the 800 MU/min CyberKnife(u00ae) at the Oscar Lambret Center (COL, France) using several commercially available detectors as well as using two passive dosimeters (EBT2 radiochromic film and micro-LiF TLD-700). The primary aim of the present work was to determine by Monte Carlo calculations the output factor in water (OFMC,w) and the Formula: see text correction factors. The secondary aim was to study the detector response in small beams using Monte Carlo simulation.\n\nMETHODS: The LINAC head of the CyberKnife(u00ae) was modeled using the PENELOPE Monte Carlo code system. The primary electron beam was modeled using a monoenergetic source with a radial gaussian distribution. The model was adjusted by comparisons between calculated and measured lateral profiles and tissue-phantom ratios obtained with the largest field. In addition, the PTW 60016 and 60017 diodes, PTW 60003 diamond, and micro-LiF were modeled. Output ratios with modeled detectors (ORMC,det) and OFMC,w were calculated and compared to measurements, in order to validate the model for smallest fields and to calculate Formula: see text correction factors, respectively. For the study of the influence of detector characteristics on their response in small beams; first, the impact of the atomic composition and the mass density of silicon, LiF, and diamond materials were investigated; second, the material, the volume averaging, and the coating effects of detecting material on the detector responses were estimated. Finally, the influence of the size of silicon chip on diode response was investigated.\n\nRESULTS: Looking at measurement ratios (uncorrected output factors) compared to the OFMC,w, the PTW 60016, 60017 and Sun Nuclear EDGE diodes systematically over-responded (about +6% for the 5 mm field), whereas the PTW 31014 Pinpoint chamber systematically under-responded (about -12% for the 5 mm field). ORdet measured with the SFD diode and PTW 60003 diamond detectors were in good agreement with OFMC,w except for the 5 mm field size (about -7.5% for the diamond and +3% for the SFD). A good agreement with OFMC,w was obtained with the EBT2 film and micro-LiF dosimeters (deviation less than 1.4% for all fields investigated). Formula: see text correction factors for several detectors used in this work have been calculated. The impact of atomic composition on the dosimetric response of detectors was found to be insignificant,u2026”, “author” : { “dropping-particle” : “”, “family” : “Moignier”, “given” : “C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huet”, “given” : “C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Makovicka”, “given” : “L”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “7”, “issued” : { “date-parts” : “2014” }, “page” : “071702”, “title” : “Determination of the \kclinMSR correction factors for detectors used with an 800 MU/min CyberKnife(\textregistered) system equipped with fixed collimators and a study of detector response to small photon beams using a Monte Carlo method”, “type” : “article-journal”, “volume” : “41” }, “uris” : “http://www.mendeley.com/documents/?uuid=47ef7f1a-8c96-4671-b5ae-41b508416201” } , “mendeley” : { “formattedCitation” : “;sup;24;/sup;”, “plainTextFormattedCitation” : “24”, “previouslyFormattedCitation” : “;sup;24;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }24,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/19/5873”, “ISSN” : “1361-6560”, “PMID” : “25211368”, “abstract” : “The recently commercialized PTW microDiamond detector (T60019) has been designed for use in small radiation fields. Here we report on the measurement of relative output ratios for small fields using five microDiamond detectors. All of the microDiamond detectors over-responded in fields smaller than 20 mm, by up to 9.3% for a 4 mm field. The over-response was independent of accelerator type and choice of collimation. The over-response was slightly larger than that observed in silicon diodes. Since all five microDiamond detectors showed the same over-response the corrections presented here should be transferable to other examples of the microDiamond detector, provided that the detector meets the manufacturing specifications and the beam characteristics are comparable.”, “author” : { “dropping-particle” : “”, “family” : “Ralston”, “given” : “Anna”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Tyler”, “given” : “Madelaine”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Liu”, “given” : “Paul”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “McKenzie”, “given” : “David”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Suchowerska”, “given” : “Natalka”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “19”, “issued” : { “date-parts” : “2014” }, “page” : “5873-81”, “title” : “Over-response of synthetic microDiamond detectors in small radiation fields.”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=fc38ae49-c662-41bb-93be-8248bd064782” } , “mendeley” : { “formattedCitation” : “;sup;25;/sup;”, “plainTextFormattedCitation” : “25”, “previouslyFormattedCitation” : “;sup;25;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }25,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/60/2/905”, “ISSN” : “1361-6560”, “PMID” : “25564826”, “abstract” : “A CVD based radiation detector has recently become commercially available from the manufacturer PTW-Freiburg (Germany). This detector has a sensitive volume of 0.004 mm(3), a nominal sensitivity of 1 nC Gy(-1) and operates at 0 V. Unlike natural diamond based detectors, the CVD diamond detector reports a low dose rate dependence. The dosimetric properties investigated in this work were dose rate, angular dependence and detector sensitivity and linearity. Also, percentage depth dose, off-axis dose profiles and total scatter ratios were measured and compared against equivalent measurements performed with a stereotactic diode. A Monte Carlo simulation was carried out to estimate the CVD small beam correction factors for a 6 MV photon beam. The small beam correction factors were compared with those obtained from stereotactic diode and ionization chambers in the same irradiation conditions The experimental measurements were performed in 6 and 15 MV photon beams with the following square field sizes: 10 u00d7 10, 5 u00d7 5, 4 u00d7 4, 3 u00d7 3, 2 u00d7 2, 1.5 u00d7 1.5, 1 u00d7 1 and 0.5 u00d7 0.5 cm. The CVD detector showed an excellent signal stability (;0.2%) and linearity, negligible dose rate dependence (;0.2%) and lower response angular dependence. The percentage depth dose and off-axis dose profiles measurements were comparable (within 1%) to the measurements performed with ionization chamber and diode in both conventional and small radiotherapy beams. For the 0.5 u00d7 0.5 cm, the measurements performed with the CVD detector showed a partial volume effect for all the dosimetric quantities measured. The Monte Carlo simulation showed that the small beam correction factors were close to unity (within 1.0%) for field sizes u22651 cm. The synthetic diamond detector had high linearity, low angular and negligible dose rate dependence, and its response was energy independent within 1% for field sizes from 1.0 to 5.0 cm. This work provides new data showing the performance of the CVD detector compared against a high spatial resolution diode. It also presents a comparison of the CVD small beam correction factors with those of diode and ionization chamber for a 6 MV photon beam.”, “author” : { “dropping-particle” : “”, “family” : “Lu00e1rraga-Gutiu00e9rrez”, “given” : “Josu00e9 Manuel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ballesteros-Zebadu00faa”, “given” : “Paola”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rodru00edguez-Ponce”, “given” : “Miguel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Garcu00eda-Garduu00f1o”, “given” : “Olivia Amanda”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Galvu00e1n de la Cruz”, “given” : “Olga Olinca Galvu00e1n”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “2015” }, “page” : “905-24”, “publisher” : “IOP Publishing”, “title” : “Properties of a commercial PTW-60019 synthetic diamond detector for the dosimetry of small radiotherapy beams.”, “type” : “article-journal”, “volume” : “60” }, “uris” : “http://www.mendeley.com/documents/?uuid=217761c7-3553-477f-9d37-fb68614df06c” } , “mendeley” : { “formattedCitation” : “;sup;26;/sup;”, “plainTextFormattedCitation” : “26”, “previouslyFormattedCitation” : “;sup;26;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }26 . For example; the last device, several papers were published reporting either the experimental determination of the output factors or the MC calculated correction factors. In particular, there is a general agreement that no output correction factors have to be applied to the MD measurements for field sizes of about 10 mm or larger. On the opposing, discrepancies can be observed in the literature among the results reported for smaller fields. The results reported inADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1259/bjr.20130768”, “ISSN” : “00071285”, “PMID” : “24588671”, “abstract” : “OBJECTIVE: To evaluate a new commercial PTW-60019 microDiamond (PTW, Freiburg, Germany) synthetic single-crystal diamond detector for relative dosimetry measurements on a clinical CyberKnifeu2122 VSI (Accuray Inc., Sunnyvale, CA) system.\n\nMETHODS: Relative output factors (ROFs) were measured for collimator diameters from 5 to 60 mm, and compared with diode PTW-60017, PTW-60018 and IBA Dosimetry (Schwarzenbruck, Germany) SFD and ionization chamber (PTW-31014 PinPoint and PTW-31010 Semiflex) measurements. Beam profiles were measured at a range of depths, and collimator sizes, with the detector stem oriented both parallel and perpendicular to the central axis (CAX). Percentage depth-dose (PDD) curves were obtained for the 60-mm collimator and compared with natural Diamond Detector (PTW-60003) and ionization chamber curves to evaluate energy dependence.\n\nRESULTS: Penumbral broadening was noted on profile measurements made with the microDiamond oriented with the stem parallel to the CAX, in comparison with diodes. Oriented perpendicular to the CAX, the profile penumbra was sharper, but stem effects could not be ruled out. The PDD measurements were within 0.5% of ionization chamber measurements, indicating insignificant dose-rate dependence. The ROF for the microDiamond fell between diode and ionization chamber results. Published Monte Carlo-derived CyberKnife-specific factors were applied to the PTW-60017, PTW-60018 and PTW-31014 ROFs, and the microDiamond factors agreed within 2.0% of the mean of these.\n\nCONCLUSION: Over a range of small field relative dosimetry measurements, the microDiamond detector shows excellent spatial resolution, dose-rate independence and water equivalence.\n\nADVANCES IN KNOWLEDGE: The microDiamond is a suitable tool for commissioning stereotactic systems.”, “author” : { “dropping-particle” : “”, “family” : “Chalkley”, “given” : “A.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Heyes”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “British Journal of Radiology”, “id” : “ITEM-1”, “issue” : “1035”, “issued” : { “date-parts” : “2014” }, “title” : “Evaluation of a synthetic single-crystal diamond detector for relative dosimetry measurements on a CyberKnife???”, “type” : “article-journal”, “volume” : “87” }, “uris” : “http://www.mendeley.com/documents/?uuid=6fc9ff4c-c9ec-4a16-a6f5-d729e8ac8a4e” } , “mendeley” : { “formattedCitation” : “;sup;27;/sup;”, “plainTextFormattedCitation” : “27”, “previouslyFormattedCitation” : “;sup;27;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }27,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/19/5937”, “ISBN” : “1361-6560 (Electronic)\r0031-9155 (Linking)”, “ISSN” : “1361-6560”, “PMID” : “25210930”, “abstract” : “The purpose of this study was to derive a complete set of correction and perturbation factors for output factors (OF) and dose profiles. Modern small field detectors were investigated including a plastic scintillator (Exradin W1, SI), a liquid ionization chamber (microLion 31018, PTW), an unshielded diode (Exradin D1V, SI) and a synthetic diamond (microDiamond 60019, PTW). A Monte Carlo (MC) beam model was commissioned for use in small fields following two commissioning procedures: (1) using intermediate and moderately small fields (down to 2u00a0u00d7u00a02u00a0cm(2)) and (2) using only small fields (0.5u00a0u00d7u00a00.5u00a0cm(2)u00a0-2u00a0u00d7u00a02u00a0cm(2)). In the latter case the detectors were explicitly modelled in the dose calculation. The commissioned model was used to derive the correction and perturbation factors with respect to a small point in water as suggested by the Alfonso formalism. In MC calculations the design of two detectors was modified in order to minimize or eliminate the corrections needed. The results of this study indicate that a commissioning process using large fields does not lead to an accurate estimation of the source size, even if a 2u00a0u00d7u00a02u00a0cm(2) field is included. Furthermore, the detector should be explicitly modelled in the calculations. On the output factors, the scintillator W1 needed the smallest correction (+0.6%), followed by the microDiamond (+1.3%). Larger corrections were observed for the microLion (+2.4%) and diode D1V (-2.4%). On the profiles, significant corrections were observed out of the field on the gradient and tail regions. The scintillator needed the smallest corrections (-4%), followed by the microDiamond (-11%), diode D1V (+13%) and microLion (-15%). The major perturbations reported were due to volume averaging and high density materials that surround the active volumes. These effects presented opposite trends in both OF and profiles. By decreasing the radius of the microLion to 0.85u00a0mm we could modify the volume averaging effect in order to achieve a discrepancy less than 1% for OF and 5% for profiles compared to water. Similar results were observed for the diode D1V if the radius was increased to 1u00a0mm.”, “author” : { “dropping-particle” : “”, “family” : “Papaconstadopoulos”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Tessier”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology U6 – ctx_ver=Z39.88-2004;ctx_enc=info%3Aofi%2Fenc%3AUTF-8;rfr_id=info:sid/summon.serialssolutions.com;rft_val_fmt=info:ofi/fmt:kev:mtx:journal;rft.genre=article;rft.atitle=On+the+correction%2C+perturbation+and+modification+”, “id” : “ITEM-1”, “issue” : “19”, “issued” : { “date-parts” : “2014” }, “page” : “5937”, “title” : “On the correction, perturbation and modification of small field detectors in relative dosimetry”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=321fc159-eee6-4b54-ac03-84e57d54267c” } , “mendeley” : { “formattedCitation” : “;sup;28;/sup;”, “plainTextFormattedCitation” : “28”, “previouslyFormattedCitation” : “;sup;28;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }28,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/60/2/905”, “ISSN” : “1361-6560”, “PMID” : “25564826”, “abstract” : “A CVD based radiation detector has recently become commercially available from the manufacturer PTW-Freiburg (Germany). This detector has a sensitive volume of 0.004 mm(3), a nominal sensitivity of 1 nC Gy(-1) and operates at 0 V. Unlike natural diamond based detectors, the CVD diamond detector reports a low dose rate dependence. The dosimetric properties investigated in this work were dose rate, angular dependence and detector sensitivity and linearity. Also, percentage depth dose, off-axis dose profiles and total scatter ratios were measured and compared against equivalent measurements performed with a stereotactic diode. A Monte Carlo simulation was carried out to estimate the CVD small beam correction factors for a 6 MV photon beam. The small beam correction factors were compared with those obtained from stereotactic diode and ionization chambers in the same irradiation conditions The experimental measurements were performed in 6 and 15 MV photon beams with the following square field sizes: 10 u00d7 10, 5 u00d7 5, 4 u00d7 4, 3 u00d7 3, 2 u00d7 2, 1.5 u00d7 1.5, 1 u00d7 1 and 0.5 u00d7 0.5 cm. The CVD detector showed an excellent signal stability (;0.2%) and linearity, negligible dose rate dependence (;0.2%) and lower response angular dependence. The percentage depth dose and off-axis dose profiles measurements were comparable (within 1%) to the measurements performed with ionization chamber and diode in both conventional and small radiotherapy beams. For the 0.5 u00d7 0.5 cm, the measurements performed with the CVD detector showed a partial volume effect for all the dosimetric quantities measured. The Monte Carlo simulation showed that the small beam correction factors were close to unity (within 1.0%) for field sizes u22651 cm. The synthetic diamond detector had high linearity, low angular and negligible dose rate dependence, and its response was energy independent within 1% for field sizes from 1.0 to 5.0 cm. This work provides new data showing the performance of the CVD detector compared against a high spatial resolution diode. It also presents a comparison of the CVD small beam correction factors with those of diode and ionization chamber for a 6 MV photon beam.”, “author” : { “dropping-particle” : “”, “family” : “Lu00e1rraga-Gutiu00e9rrez”, “given” : “Josu00e9 Manuel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ballesteros-Zebadu00faa”, “given” : “Paola”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rodru00edguez-Ponce”, “given” : “Miguel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Garcu00eda-Garduu00f1o”, “given” : “Olivia Amanda”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Galvu00e1n de la Cruz”, “given” : “Olga Olinca Galvu00e1n”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “2015” }, “page” : “905-24”, “publisher” : “IOP Publishing”, “title” : “Properties of a commercial PTW-60019 synthetic diamond detector for the dosimetry of small radiotherapy beams.”, “type” : “article-journal”, “volume” : “60” }, “uris” : “http://www.mendeley.com/documents/?uuid=27bbeaf2-6acb-4ae7-968d-604f5b6813ee” } , “mendeley” : { “formattedCitation” : “;sup;26;/sup;”, “plainTextFormattedCitation” : “26”, “previouslyFormattedCitation” : “;sup;26;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }26,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/61/1/L1”, “ISSN” : “0031-9155”, “PMID” : “26630437”, “abstract” : “Monte Carlo (MC) calculated detector-specific output correction factors for small photon beam dosimetry are commonly used in clinical practice. The technique, with a geometry description based on manufacturer blueprints, offers certain advantages over experimentally determined values but is not free of weaknesses. Independent MC calculations of output correction factors for a PTW-60019 micro-diamond detector were made using the EGSnrc and PENELOPE systems. Compared with published experimental data the MC results showed substantial disagreement for the smallest field size simulated (5 mm 5 u00d7 mm). To explain the difference between the two datasets, a detector was imaged with x rays searching for possible anomalies in the detector construction or details not included in the blueprints. A discrepancy between the dimension stated in the blueprints for the active detector area and that estimated from the electrical contact seen in the x-ray image was observed. Calculations were repeated using the estimate of a smaller volume, leading to results in excellent agreement with the experimental data. MC users should become aware of the potential differences between the design blueprints of a detector and its manufacturer production, as they may differ substantially. The constraint is applicable to the simulation of any detector type. Comparison with experimental data should be used to reveal geometrical inconsistencies and details not included in technical drawings, in addition to the well-known QA procedure of detector x-ray imaging.”, “author” : { “dropping-particle” : “”, “family” : “Andreo”, “given” : “Pedro”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “Hugo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marteinsdu00f3ttir”, “given” : “Maria”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Benmakhlouf”, “given” : “Hamza”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Carlsson-Tedgren”, “given” : “u00c5sa”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in Medicine and Biology”, “id” : “ITEM-1”, “issued” : { “date-parts” : “2016” }, “page” : “L1-L10”, “title” : “On the Monte Carlo simulation of small-field micro-diamond detectors for megavoltage photon dosimetry”, “type” : “article-journal”, “volume” : “61” }, “uris” : “http://www.mendeley.com/documents/?uuid=97c53c4f-9bb0-4c78-a6fc-20dd1c18f677” } , “mendeley” : { “formattedCitation” : “;sup;29;/sup;”, “plainTextFormattedCitation” : “29”, “previouslyFormattedCitation” : “;sup;29;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }29,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4938584”, “ISSN” : “00942405”, “PMID” : “26745934”, “abstract” : “Purpose: The use of radiotherapy fields smaller than 3 cm in diameter has resulted in the need for accurate detector correction factors for small field dosimetry. However, published factors do not always agree and errors introduced by biased reference detectors, inaccurate Monte Carlo models, or experimental errors can be difficult to distinguish. The aim of this study was to provide a robust set of detector-correction factors for a range of detectors using numerical, empirical, and semiempirical techniques under the same conditions and to examine the consistency of these factors between techniques. Methods: Empirical detector correction factors were derived based on small field output factor measurements for circular field sizes from 3.1 to 0.3 cm in diameter performed with a 6 MV beam. A PTW 60019 microDiamond detector was used as the reference dosimeter. Numerical detector correction factors for the same fields were derived based on calculations from a geant4 Monte Carlo model of the detectors and the Linac treatment head. Semiempirical detector correction factors were derived from the empirical output factors and the numerical dose-to-water calculations. Results: The PTW 60019 microDiamond was found to over-respond at small field sizes resulting in a bias in the empirical detector correction factors. The over-response was similar in magnitude to that of the unshielded diode. Good agreement was generally found between semiempirical and numerical detector correction factors except for the PTW 60016 Diode P, where the numerical values showed a greater over-response than the semiempirical values by a factor of 3.7% for a 1.1 cm diameter field and higher for smaller fields. Conclusions: Detector correction factors based solely on empirical measurement or numerical calculation are subject to potential bias. A semiempirical approach, combining both empirical and numerical data, provided the most reliable results.”, “author” : { “dropping-particle” : “”, “family” : “O’Brien”, “given” : “Daniel J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Leu00f3n-Vintru00f3”, “given” : “Luis”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “McClean”, “given” : “Brendan”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “2016” }, “page” : “411”, “title” : “Small field detector correction factors kQclin, Qmsrfclin, fmsr for silicon-diode and diamond detectors with circular 6 MV fields derived using both empirical and numerical methods”, “type” : “article-journal”, “volume” : “43” }, “uris” : “http://www.mendeley.com/documents/?uuid=8447303d-dd21-4b6b-87d7-0322437ce855” } , “mendeley” : { “formattedCitation” : “<sup>30</sup>”, “plainTextFormattedCitation” : “30”, “previouslyFormattedCitation” : “<sup>30</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }30showed an increase of the correction factors below 10 mm. In principle, such differences might be attributed to: (i) random MD response fluctuations, (ii) different experimental setups, (iii) different measuring protocols, (iv) MC modeling issues, and (v) choice of reference detectors.

Diamond shows properties attracting for dosimetric applications, in fact, it is almost soft-tissue equivalent, chemically inert, nontoxic, and presents mechanical stability and high radiation hardness, i.e., its sensitivity is constant with the accumulated dose. These features, along with high sensitivity to radiation, permit to build small volume detectors for a specific radiation type, being either photons or electrons, the diamond response is independent of the beam energyADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.1446101”, “abstract” : “The dosimetric properties of two PTW Riga diamond detectors type 60003 were studied in highu2010energy photon and electron therapy beam. Properties under study were currentu2013voltage characteristic, polarization effect, time stability of response, dose response, doseu2010rate dependence, temperature stability, and beam quality dependence of the sensitivity factor. Differences were shown between the two detectors for most of the previous properties. Also, the observed behavior was, to some extent, different from what was reported in the PTW technical specifications. The necessity to characterize each diamond detector individually was addressed.”, “author” : { “dropping-particle” : “”, “family” : “C.”, “given” : “De Angelis”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “S.”, “given” : “Onori”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “M.”, “given” : “Pacilio”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “P.”, “given” : “Cirrone G A”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “G.”, “given” : “Cuttone”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “L.”, “given” : “Raffaele”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “M.”, “given” : “Bucciolini”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “S.”, “given” : “Mazzocchi”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “0” }, “page” : “248-254”, “title” : “An investigation of the operating characteristics of two PTW diamond detectors in photon and electron beams”, “type” : “article-journal”, “volume” : “29” }, “uris” : “http://www.mendeley.com/documents/?uuid=a4738d14-c021-4a25-a5d0-ce0d3f72a287”, “http://www.mendeley.com/documents/?uuid=42bd2921-bea9-440e-a3c8-a80fd5363552” } , “mendeley” : { “formattedCitation” : “<sup>31</sup>”, “plainTextFormattedCitation” : “31”, “previouslyFormattedCitation” : “<sup>31</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }31
In small fields, detector readings are affected both by volume-averaging and by the densities of the detector sensitive volume and surrounding components. To a slighter extent, atomic number also affects detector readings, via differences between photon spectra in broad and narrow fields. When evaluating the accuracy of dosimetric measurements it should be established whether any part of the detector sensitive volume lies within a distance lower than the radius where the lateral electronic equilibrium breaks down; and if so, whether the electron fluence will be greatly perturbed by a detector of the size, density and composition used, and whether accurate correction factors are available to account for the resulting perturbation and volume-averaging. An ideal detector would provide the dose at a point, would be energy independent and would require only a single calibration valid for all possible energies and irradiation scenarios
Air-filled ionization chambers are lower limited in size by the signal to noise ratio, which for therapeutic dose levels requires a volume of about 0.01 cm3 to achieve a signal to noise ratio of around 1000. For such small chambers, radiation-induced stem currents and cable currents become very large compared to the signal. The diodes give values of OF significantly greater than ? (the OF in water) for fields lower than 10 mm in diameter and correction factors must be applied.

New types of a detector which offer advantages for small field dosimetry over diodes in terms of water equivalence, and air-filled microchambers in terms of volume averaging and density variation, are commercially available. One such is a point scintillation detector which combines good water equivalence and a small sensitive volume ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4903757”, “ISBN” : “0094-2405”, “ISSN” : “0094-2405”, “PMID” : “26133640”, “abstract” : “To evaluate the main characteristics of the Exradin W1 scintillator as a dosimeter and to estimate measurement uncertainties when used in radiotherapy. We studied the calibration procedure, energy and modality dependence, short-term repeatability, dose-response linearity, angular dependence, temperature dependence, time to reach thermal equilibrium, dose-rate dependence, water-equivalent depth of the effective measurement point, and long-term stability. An uncertainty budget was derived for relative and absolute dose measurements in photon and electron beams. Exradin W1 showed a temperature dependence of -0.225% u00b0C(-1). The loss of sensitivity with accumulated dose decreased with use. The sensitivity of Exradin W1 was energy independent for high-energy photon and electron beams. All remaining dependencies of Exradin W1 were around or below 0.5%, leading to an uncertainty budget of about 1%. When a dual channel electrometer with automatic trigger was not used, timing effects became significant, increasing uncertainties by one order of magnitude. The Exradin W1 response is energy independent for high energy x-rays and electron beams, and only one calibration coefficient is needed. A temperature correction factor should be applied to keep uncertainties around 2% for absolute dose measurements and around 1% for relative measurements in high-energy photon and electron beams. The Exradin W1 scintillator is an excellent alternative to detectors such as diodes for relative dose measurements.”, “author” : { “dropping-particle” : “”, “family” : “Carrasco”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Jornet”, “given” : “N”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Jordi”, “given” : “O”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Lizondo”, “given” : “M”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Latorre-Musoll”, “given” : “A”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Eudaldo”, “given” : “T”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ruiz”, “given” : “A”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ribas”, “given” : “M”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “2015” }, “page” : “297”, “title” : “Characterization of the Exradin W1 scintillator for use in radiotherapy”, “type” : “article-journal”, “volume” : “42” }, “uris” : “http://www.mendeley.com/documents/?uuid=adf1dec0-127a-400b-988d-06fd41e28625” } , “mendeley” : { “formattedCitation” : “<sup>32</sup>”, “plainTextFormattedCitation” : “32”, “previouslyFormattedCitation” : “<sup>32</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }32 Francescon et al calculated correction factors for OF measurement with this detector as ? 0.3% for all VSI system circular collimators, although this wasn’t verified by measurement ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/6/N11”, “ISBN” : “1361-6560 (Electronic)\r0031-9155 (Linking)”, “ISSN” : “1361-6560”, “PMID” : “24594929”, “abstract” : “A previous study of the corrections needed for output factor measurements with the CyberKnife system has been extended to include new diode detectors (IBA SFD and Exradin D1V), an air filled microchamber (Exradin CC01) and a scintillation detector (Exradin W1). The dependence of the corrections on detector orientation (detector long axis parallel versus perpendicular to the beam axis) and source to detector distance (SDD) was evaluated for these new detectors and for those in our previous study. The new diodes are found to over-respond at the smallest (5 mm) field size by 2.5% (D1V) and 3.3% (SFD) at 800 mm SDD, while the CC01 under-responds by 7.4% at the same distance when oriented parallel to the beam. Corrections for all detectors tend to unity as field size increases. The W1 corrections are <0.5% at all field sizes. Microchamber correction factors increase substantially if the detector is oriented perpendicular to the beam (by up to 23% for the PTW 31014). Corrections also vary with SDD, with the largest variations seen for microchambers in the perpendicular orientation (up to 13% change at 650 mm SDD versus 800 mm) and smallest for diodes (~1% change at 650 mm versus 800 mm). The smallest and most stable corrections are found for diodes, liquid filled microchambers and scintillation detectors, therefore these should be preferred for small field output factor measurements. If air filled microchambers are used, then the parallel orientation should be preferred to the perpendicular, and care should be taken to use corrections appropriate to the measurement SDD.”, “author” : { “dropping-particle” : “”, “family” : “Francescon”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Satariano”, “given” : “N”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “6”, “issued” : { “date-parts” : “2014” }, “page” : “N11-7”, “title” : “Monte Carlo simulated correction factors for output factor measurement with the CyberKnife system-results for new detectors and correction factor dependence on measurement distance and detector orientation.”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=e4342840-5659-4fa3-93f7-dd3fa78a80bc” } , “mendeley” : { “formattedCitation” : “<sup>23</sup>”, “plainTextFormattedCitation” : “23”, “previouslyFormattedCitation” : “<sup>23</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }23 A subsequent multi-center study comparing OF measurements to corrected diode measurements showed an average agreement of ? 1.0% for all CyberKnife circular fields and a study using another 6 MV treatment beam with similar field sizes reported corrections of ? 0.6% ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/19/5937”, “ISBN” : “1361-6560 (Electronic)\r0031-9155 (Linking)”, “ISSN” : “1361-6560”, “PMID” : “25210930”, “abstract” : “The purpose of this study was to derive a complete set of correction and perturbation factors for output factors (OF) and dose profiles. Modern small field detectors were investigated including a plastic scintillator (Exradin W1, SI), a liquid ionization chamber (microLion 31018, PTW), an unshielded diode (Exradin D1V, SI) and a synthetic diamond (microDiamond 60019, PTW). A Monte Carlo (MC) beam model was commissioned for use in small fields following two commissioning procedures: (1) using intermediate and moderately small fields (down to 2u00a0u00d7u00a02u00a0cm(2)) and (2) using only small fields (0.5u00a0u00d7u00a00.5u00a0cm(2)u00a0-2u00a0u00d7u00a02u00a0cm(2)). In the latter case the detectors were explicitly modelled in the dose calculation. The commissioned model was used to derive the correction and perturbation factors with respect to a small point in water as suggested by the Alfonso formalism. In MC calculations the design of two detectors was modified in order to minimize or eliminate the corrections needed. The results of this study indicate that a commissioning process using large fields does not lead to an accurate estimation of the source size, even if a 2u00a0u00d7u00a02u00a0cm(2) field is included. Furthermore, the detector should be explicitly modelled in the calculations. On the output factors, the scintillator W1 needed the smallest correction (+0.6%), followed by the microDiamond (+1.3%). Larger corrections were observed for the microLion (+2.4%) and diode D1V (-2.4%). On the profiles, significant corrections were observed out of the field on the gradient and tail regions. The scintillator needed the smallest corrections (-4%), followed by the microDiamond (-11%), diode D1V (+13%) and microLion (-15%). The major perturbations reported were due to volume averaging and high density materials that surround the active volumes. These effects presented opposite trends in both OF and profiles. By decreasing the radius of the microLion to 0.85u00a0mm we could modify the volume averaging effect in order to achieve a discrepancy less than 1% for OF and 5% for profiles compared to water. Similar results were observed for the diode D1V if the radius was increased to 1u00a0mm.”, “author” : { “dropping-particle” : “”, “family” : “Papaconstadopoulos”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Tessier”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology U6 – ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=On+the+correction%2C+perturbation+and+modification+”, “id” : “ITEM-1”, “issue” : “19”, “issued” : { “date-parts” : “2014” }, “page” : “5937”, “title” : “On the correction, perturbation and modification of small field detectors in relative dosimetry”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=321fc159-eee6-4b54-ac03-84e57d54267c” } , “mendeley” : { “formattedCitation” : “<sup>28</sup>”, “plainTextFormattedCitation” : “28”, “previouslyFormattedCitation” : “<sup>28</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }28.

For these reasons we have tested other types of dosimeters in this current work: microLion, microdiamond, diode and scintillating detector response in small fields are carried out, by measuring output factor. The obtained results provide an assessment of the MD dosimetric properties in view of its application in small field reference dosimetry. Also, Because of most of the published article lack a proper estimation of the uncertainty in the various steps involved in the determination of output factor and the correction factors we will study the uncertainty of our detectors.

Materials and methods
II.A. Detectors
No commercial detector has all the properties necessary to achieve accurate dosimetry in small fields; thus, none can be used as a reference without correction factors. We compared the output factors and Field factors with their uncertainty of four detectors and to characterize the strong point and weak point of each dosimeter for small-field dosimetry.

All the detectors used are described below.

II.A.1. PTW 60019 MicroDiamondDiamond detectors are solid state detectors combining small size and high response. In addition, their response is almost independent upon energy, i.e. they are very much water equivalent. They also feature a very good directional response. Diamond detectors can be constructed as solid state ionization chambers (TM60003 diamond) or as diodes (T60019 microDiamond). The active volume implanted in the diamond crystal has a cylindrical shape of 1.1 mm radius and length of 1 mm. The reference point is on the detector axis, 1 mm from the tip, marked by a ring. In all measurements, the two microDiamond dosimeters were oriented with their axis parallel to the beam direction with the detector facing up with the gantry at zero degrees, as recommended by literature and manufacturers ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4729739”, “ISBN” : “00942405 (ISSN)”, “ISSN” : “00942405”, “PMID” : “22830781”, “abstract” : “PURPOSE: To determine the potentialities of synthetic single crystal diamond Schottky diodes for accurate dose measurements in radiation therapy small photon beams.\n\nMETHODS: The dosimetric properties of a diamond-based detector were assessed by comparison with a reference microionization chamber. The diamond device was operated at zero bias voltage under irradiation with high-energy radiotherapic photon beams. The stability of the detector response and its dose and dose rate dependence were measured. Different square field sizes ranging from 1 u00d7 1 cm(2) to 10 u00d7 10 cm(2) were used during comparative dose distribution measurements by means of percentage depth dose curves (PDDs), lateral beam profiles, and output factors. The angular and temperature dependence of the diamond detector response were also studied.\n\nRESULTS: The detector response shows a deviation from linearity of less than u00b10.5% in the 0.01-7 Gy range and dose rate dependence below u00b10.5% in the 1-6 Gyu2215min range. PDDs and output factors are in good agreement with those measured by the reference ionization chamber within 1%. No angular dependence is observed by rotating the detector along its axis, while u223c3.5% maximum difference is measured by varying the radiation incidence angle in the polar direction. The temperature dependence was investigated as well and a u00b10.2% variation of the detector response is found in the 18-40 u00b0C range.\n\nCONCLUSIONS: The obtained results indicate the investigated synthetic diamond-based detector as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.”, “author” : { “dropping-particle” : “”, “family” : “Ciancaglioni”, “given” : “I.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Milani”, “given” : “E.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Prestopino”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona”, “given” : “C.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Consorti”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Petrucci”, “given” : “a.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Notaristefani”, “given” : “F.”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “7”, “issued” : { “date-parts” : “2012” }, “page” : “4493”, “title” : “Dosimetric characterization of a synthetic single crystal diamond detector in clinical radiation therapy small photon beams”, “type” : “article-journal”, “volume” : “39” }, “uris” : “http://www.mendeley.com/documents/?uuid=a5288c2b-212d-4603-8593-50d88db599d0” } , “mendeley” : { “formattedCitation” : “<sup>16</sup>”, “plainTextFormattedCitation” : “16”, “previouslyFormattedCitation” : “<sup>16</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }16,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1016/j.nima.2009.07.004”, “ISBN” : “0168-9002”, “ISSN” : “01689002”, “abstract” : “A synthetic single crystal diamond Schottky diode, in a p-type/intrinsic/metal structure, deposited by Chemical Vapour Deposition (CVD) and operating in photovoltaic regime, with no external bias voltage applied, was tested as a dosimeter for Intensity Modulated Radiation Therapy (IMRT) applications. The device response was compared with dose measurements from two commercial ionization chambers and a 2D diode array in an IMRT prostate cancer treatment plan. The obtained results indicate that CVD synthetic single crystal diamond-based dosimeters can successfully be used for highly conformed radiotherapy and IMRT dosimetry, due to their small size and high sensitivity per unit volume. u00a9 2009 Elsevier B.V. All rights reserved.”, “author” : { “dropping-particle” : “”, “family” : “Almaviva”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ciancaglioni”, “given” : “I.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Consorti”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Notaristefani”, “given” : “F.”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Manfredotti”, “given” : “C.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Milani”, “given” : “E.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Petrucci”, “given” : “A.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Prestopino”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona”, “given” : “C.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “2009” }, “page” : “191-194”, “publisher” : “Elsevier”, “title” : “Synthetic single crystal diamond dosimeters for Intensity Modulated Radiation Therapy applications”, “type” : “article-journal”, “volume” : “608” }, “uris” : “http://www.mendeley.com/documents/?uuid=0c576b8b-e6f7-4cf5-83c3-8393d2abf36f” } , “mendeley” : { “formattedCitation” : “<sup>33</sup>”, “plainTextFormattedCitation” : “33”, “previouslyFormattedCitation” : “<sup>33</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }33, ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4927569”, “ISSN” : “0094-2405”, “abstract” : “u00a9 2015 American Association of Physicists in Medicine u00a9 2015 Am. Assoc. Phys. Med.Purpose: To evaluate the new commercial PTW-60019 synthetic single-crystal microDiamond detector (PTW, Freiburg, Germany) for relative dosimetry measurements on a clinical Leksell Gamma Knife Perfexion radiosurgery system. Methods: Detector output ratios (DORs) for 4 and 8 mm beams were measured using a micro- Diamond (PTW-60019), a stereotactic unshielded diode IBA stereotactic field detector (SFD), a shielded diode (IBA photon field detector), and GafChromic EBT3 films. Both parallel and transversal acquisition directions were considered for PTW-60019 measurements. Measured DORs were compared to the new output factor reference values for Gamma Knife Perfexion (0.814 and 0.900 for 4 and 8 mm, respectively). Profiles in the three directions were also measured for the 4 mm beam to evaluate full width at half maximum (FWHM) and penumbra and to compare them with the corresponding Leksell GammaPlan profiles. Results: FWHM and penumbra for PTW-60019 differed from the calculated values by less than 0.2 and 0.3 mm, for the parallel and transversal acquisitions, respectively. GafChromic films showed FWHM and penumbra within 0.1 mm. The output ratio obtained with the PTW-60019 for the 4 mm field was 1.6% greater in transverse direction compared to the nominal value. Comparable differences up to 0.8% and 1.0% for, respectively, GafChromic films and SFD were found. Conclusions: The microDiamond PTW-60019 is a suitable detector for commissioning and routine use of Gamma Knife with good agreement of both DORs and profiles in the three directions.”, “author” : { “dropping-particle” : “”, “family” : “Mancosu”, “given” : “Pietro”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Reggiori”, “given” : “Giacomo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Stravato”, “given” : “Antonella”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Gaudino”, “given” : “Anna”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Lobefalo”, “given” : “Francesca”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palumbo”, “given” : “Valentina”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Navarria”, “given” : “Piera”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ascolese”, “given” : “Anna”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Picozzi”, “given” : “Piero”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “Gianluca”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Tomatis”, “given” : “Stefano”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Scorsetti”, “given” : “Marta”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “9”, “issued” : { “date-parts” : “2015” }, “page” : “5035-5041”, “title” : “Evaluation of a synthetic single-crystal diamond detector for relative dosimetry on the Leksell Gamma Knife Perfexion radiosurgery system”, “type” : “article-journal”, “volume” : “42” }, “uris” : “http://www.mendeley.com/documents/?uuid=67a82a98-b75d-45d9-aba9-c2670e2e7ecb” } , “mendeley” : { “formattedCitation” : “<sup>34</sup>”, “plainTextFormattedCitation” : “34”, “previouslyFormattedCitation” : “<sup>34</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }34,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/60/2/905”, “ISSN” : “1361-6560”, “PMID” : “25564826”, “abstract” : “A CVD based radiation detector has recently become commercially available from the manufacturer PTW-Freiburg (Germany). This detector has a sensitive volume of 0.004 mm(3), a nominal sensitivity of 1 nC Gy(-1) and operates at 0 V. Unlike natural diamond based detectors, the CVD diamond detector reports a low dose rate dependence. The dosimetric properties investigated in this work were dose rate, angular dependence and detector sensitivity and linearity. Also, percentage depth dose, off-axis dose profiles and total scatter ratios were measured and compared against equivalent measurements performed with a stereotactic diode. A Monte Carlo simulation was carried out to estimate the CVD small beam correction factors for a 6 MV photon beam. The small beam correction factors were compared with those obtained from stereotactic diode and ionization chambers in the same irradiation conditions The experimental measurements were performed in 6 and 15 MV photon beams with the following square field sizes: 10 u00d7 10, 5 u00d7 5, 4 u00d7 4, 3 u00d7 3, 2 u00d7 2, 1.5 u00d7 1.5, 1 u00d7 1 and 0.5 u00d7 0.5 cm. The CVD detector showed an excellent signal stability (<0.2%) and linearity, negligible dose rate dependence (<0.2%) and lower response angular dependence. The percentage depth dose and off-axis dose profiles measurements were comparable (within 1%) to the measurements performed with ionization chamber and diode in both conventional and small radiotherapy beams. For the 0.5 u00d7 0.5 cm, the measurements performed with the CVD detector showed a partial volume effect for all the dosimetric quantities measured. The Monte Carlo simulation showed that the small beam correction factors were close to unity (within 1.0%) for field sizes u22651 cm. The synthetic diamond detector had high linearity, low angular and negligible dose rate dependence, and its response was energy independent within 1% for field sizes from 1.0 to 5.0 cm. This work provides new data showing the performance of the CVD detector compared against a high spatial resolution diode. It also presents a comparison of the CVD small beam correction factors with those of diode and ionization chamber for a 6 MV photon beam.”, “author” : { “dropping-particle” : “”, “family” : “Lu00e1rraga-Gutiu00e9rrez”, “given” : “Josu00e9 Manuel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ballesteros-Zebadu00faa”, “given” : “Paola”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rodru00edguez-Ponce”, “given” : “Miguel”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Garcu00eda-Garduu00f1o”, “given” : “Olivia Amanda”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Galvu00e1n de la Cruz”, “given” : “Olga Olinca Galvu00e1n”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology”, “id” : “ITEM-1”, “issue” : “2”, “issued” : { “date-parts” : “2015” }, “page” : “905-24”, “publisher” : “IOP Publishing”, “title” : “Properties of a commercial PTW-60019 synthetic diamond detector for the dosimetry of small radiotherapy beams.”, “type” : “article-journal”, “volume” : “60” }, “uris” : “http://www.mendeley.com/documents/?uuid=217761c7-3553-477f-9d37-fb68614df06c” } , “mendeley” : { “formattedCitation” : “<sup>26</sup>”, “plainTextFormattedCitation” : “26”, “previouslyFormattedCitation” : “<sup>26</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }26,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/60/17/6669”, “ISSN” : “0031-9155”, “PMID” : “26271097”, “abstract” : “In this work we use EBT3 film measurements at 10 MV to demonstrate the suitability of the Exradin W1 (plastic scintillator) for relative dosimetry within small photon fields. We then use the Exradin W1 to measure the small field correction factors required by two other detectors: the PTW unshielded Ediode 60017 and the PTW microDiamond 60019. We consider on-axis correction-factors for small fields collimated using MLCs for four different TrueBeam energies: 6 FFF, 6 MV, 10 FFF and 10 MV. We also investigate percentage depth dose and lateral profile perturbations. In addition to high-density effects from its silicon sensitive region, the Ediode exhibited a dose-rate dependence and its known over-response to low energy scatter was found to be greater for 6 FFF than 6 MV. For clinical centres without access to a W1 scintillator, we recommend the microDiamond over the Ediode and suggest that ‘limits of usability’, field sizes below which a detector introduces unacceptable errors, can form a practical alternative to small-field correction factors. For a dosimetric tolerance of 2% on-axis, the microDiamond might be utilised down to 10 mm and 15 mm field sizes for 6 MV and 10 MV, respectively.”, “author” : { “dropping-particle” : “”, “family” : “Underwood”, “given” : “T S A”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rowland”, “given” : “B C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ferrand”, “given” : “R”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vieillevigne”, “given” : “L”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in Medicine and Biology”, “id” : “ITEM-1”, “issue” : “17”, “issued” : { “date-parts” : “2015” }, “page” : “6669-6683”, “publisher” : “IOP Publishing”, “title” : “Application of the Exradin W1 scintillator to determine Ediode 60017 and microDiamond 60019 correction factors for relative dosimetry within small MV and FFF fields”, “type” : “article-journal”, “volume” : “60” }, “uris” : “http://www.mendeley.com/documents/?uuid=70e1e685-0561-4b20-9c94-a9e4946f4406” } , “mendeley” : { “formattedCitation” : “<sup>35</sup>”, “plainTextFormattedCitation” : “35”, “previouslyFormattedCitation” : “<sup>35</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }35. Diamond has long been considered a suitable material for the construction of small volume high-resolution radiation detectors due to its radiation hardness, near tissue-equivalence, small size, high-sensitivity, independence from the energy of photons and low leakage current ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1016/j.ejmp.2016.03.005”, “ISSN” : “1724191X”, “abstract” : “Purpose: The aim of the present work was to evaluate small field size output factors (OFs) using the latest diamond detector commercially available, PTW-60019 microDiamond, over different CyberKnife systems. OFs were measured also by silicon detectors routinely used by each center, considered as reference. Methods: Five Italian CyberKnife centers performed OFs measurements for field sizes ranging from 5 to 60 mm, defined by fixed circular collimators (5 centers) and by Iris??? variable aperture collimator (4 centers). Setup conditions were: 80 cm source to detector distance, and 1.5 cm depth in water. To speed up measurements two diamond detectors were used and their equivalence was evaluated. MonteCarlo (MC) correction factors for silicon detectors were used for comparing the OF measurements. Results: Considering OFs values averaged over all centers, diamond data resulted lower than uncorrected silicon diode ones. The agreement between diamond and MC corrected silicon values was within 0.6% for all fixed circular collimators. Relative differences between microDiamond and MC corrected silicon diodes data for Iris??? collimator were lower than 1.0% for all apertures in the totality of centers. The two microDiamond detectors showed similar characteristics, in agreement with the technical specifications. Conclusions: Excellent agreement between microDiamond and MC corrected silicon diode detectors OFs was obtained for both collimation systems fixed cones and Iris???, demonstrating the microDiamond could be a suitable detector for CyberKnife commissioning and routine checks. These results obtained in five centers suggest that for CyberKnife systems microDiamond can be used without corrections even at the smallest field size.”, “author” : { “dropping-particle” : “”, “family” : “Russo”, “given” : “Serenella”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Masi”, “given” : “Laura”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Francescon”, “given” : “Paolo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Frassanito”, “given” : “Maria Cristina”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fumagalli”, “given” : “Maria Luisa”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Falco”, “given” : “Maria Daniela”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Martinotti”, “given” : “Anna Stefania”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Pimpinella”, “given” : “Maria”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Reggiori”, “given” : “Giacomo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona Rinati”, “given” : “Gianluca”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vigorito”, “given” : “Sabrina”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mancosu”, “given” : “Pietro”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physica Medica”, “id” : “ITEM-1”, “issue” : “4”, “issued” : { “date-parts” : “2016” }, “page” : “575-581”, “publisher” : “Associazione Italiana di Fisica Medica”, “title” : “Multicenter evaluation of a synthetic single-crystal diamond detector for CyberKnife small field size output factors”, “type” : “article-journal”, “volume” : “32” }, “uris” : “http://www.mendeley.com/documents/?uuid=8d2916b7-b183-43db-9771-3fb2fcf0d29d” } , “mendeley” : { “formattedCitation” : “<sup>36</sup>”, “plainTextFormattedCitation” : “36”, “previouslyFormattedCitation” : “<sup>36</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }36 ,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.1591431”, “ISBN” : “00942405”, “ISSN” : “00942405”, “PMID” : “12945980”, “abstract” : “The aim of this work was to test the suitability of a PTW diamond detector for nonreference condition dosimetry in photon beams of different energy (6 and 25 MV) and field size (from 2.6 cm x 2.6 cm to 10 cm x 10 cm). Diamond behavior was compared to that of a Scanditronix p-type silicon diode and a Scanditronix RK ionization chamber. Measurements included output factors (OF). percentage depth doses (PDD) and dose profiles. OFs measured with diamond detector agreed within 1% with those measured with diode and RK chamber. Only at 25 MV, for the smallest field size, RK chamber underestimated OFs due to averaging effects in a pointed shaped beam profile. Agreement was found between PDDs measured with diamond detector and RK chamber for both 6 MV and 25 MV photons and down to 5 cm x 5 cm field size. For the 2.6 cm x 2.6 cm field size, at 25 MV, RK chamber underestimated doses at shallow depth and the difference progressively went to zero in the distal region. PDD curves measured with silicon diode and diamond detector agreed well for the 25 MV beam at all the field sizes. Conversely, the nontissue equivalence of silicon led, for the 6 MV beam, to a slight overestimation of the diode doses in the distal region, at all the field sizes. Penumbra and field width measurements gave values in agreement for all the detectors but with a systematic overestimate by RK measurements. The results obtained confirm that ion chamber is not a suitable detector when high spatial resolution is required. On the other hand, the small differences in the studied parameters, between diamond and silicon systems, do not lead to a significant advantage in the use of diamond detector for routine clinical dosimetry.”, “author” : { “dropping-particle” : “”, “family” : “Bucciolini”, “given” : “Martha”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Buonamici”, “given” : “F. Banci”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mazzocchi”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Angelis”, “given” : “C.”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Onori”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Cirrone”, “given” : “G. A.P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2003” }, “page” : “2149-2154”, “title” : “Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size”, “type” : “article-journal”, “volume” : “30” }, “uris” : “http://www.mendeley.com/documents/?uuid=fce60146-24be-45f9-bca2-da750b9d5a24” } , “mendeley” : { “formattedCitation” : “<sup>37</sup>”, “plainTextFormattedCitation” : “37”, “previouslyFormattedCitation” : “<sup>37</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }37
II.A.2. PTW 31018 MicroLion chamber
The microLion (Physikalisch-Technische Werkstätten) was recently developed specifically for small-field dosimetry. The sensitive volume in this chamber is composed of isooctane (C8H18) rather than air, enabling the sensitive volume to be reduced to 1.7 mm3, and a high electrical signal response is conserved for a given dose. The design is a parallel plate chamber with a diameter of 2.5 mm and electrode spacing of 0.35 mm. The entrance window is composed of polystyrene, graphite, and varnish. The central electrode is made of graphite only. The ionization chamber type 31018 is designed for use in connection with the PTW dosemeters UNIDOSwebline or TANDEM PTW dosemeters and the external high voltage source HV-Supply
II.A.3. diode
Silicon diode detectors feature the highest response per volume of all common detector types. Hence their sensitive volume is usually small enough to avoid dose-volume effects down to very small fields. However, the density perturbation effect is still present. The directional response of silicon diodes is not ideal, as well as the response to low-energy scattered photons. To reduce the latter effect, diodes exist in a shielded design where the shield reduces the signal from these photons. In small fields, the low-energy scatter contribution is low, hence diode shielding is not needed and unshielded diodes are recommended for small fields ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “author” : { “dropping-particle” : “”, “family” : “Aspradakis”, “given” : “M.M.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Byrne”, “given” : “J.P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Duane”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Conway”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Warrington”, “given” : “A.P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “id” : “ITEM-1”, “issued” : { “date-parts” : “2010” }, “title” : “IPEM report 103: Small field MV photon dosimetry”, “type” : “article” }, “uris” : “http://www.mendeley.com/documents/?uuid=e66a143e-4ba4-341e-8e68-a566b2c88c16” } , “mendeley” : { “formattedCitation” : “<sup>11</sup>”, “plainTextFormattedCitation” : “11”, “previouslyFormattedCitation” : “<sup>11</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }11.

II.A.4. PSD
PSD was composed of a cylindrical scintillating fiber (multicladding SCSF-78M, Kuraray Co., Ltd., Tokyo, Japan) with a diameter of 0.5 mm and a length of 1.0 mm coupled with a PMMA optical fiber (Super Eska SH-2001, Mitsubishi, Rayon Co., Ltd., Tokyo, Japan) with a diameter of 0.5 mm and a length of 5 m to guide the scintillation produced to a polychromatic charge-coupled device (CCD) (U2000c, Apogee Imaging System, Roseville, CA, USA). A light collection system was developed to maximize the signal-to-noise ratio (SNR) using an optical lens (Minolta MC Rokkor-X PG, f/# = 1.4, focal length = 50 mm).

II.B. Experimental setups
Measurements were performed with:
(i)a CyberKnife® Robotic Radiosurgery System (Accuray Incorporated, Sunnyvale, CA, USA). at the Department of Medical Physics, ULSS, Vicenza, Italy; (ii) the measurements were performed in a PTW MP3 water tank with a spatial position accuracy of ±0.1 mm was used for scanning all detectors, by positioning the MD, diode, ML and Plastic Scintillator Detector (PSD) detectors were used with their stems parallel to the beam axis ( parallel orientation). No bias voltage was applied to MD and 800 V was applied to Ml, according to the manufacturer’s instructions. The PTW TRUFIXR detector positioning system was used for MD and ML, so to improve the depth positioning accuracy in the water phantom.

CK measurements were performed in a 6 MV flattening-filter-free beam (TPR20/10 = 0.640 at a field size of 60 mm in diameter), delivered at 800 MU min?1 and collimated by using circular fixed tungsten cones. Field sizes with nominal diameters of 60 mm, 50 mm, 40 mm, 35 mm, 30 mm, 25 mm, 20 mm, 15 mm, 12.5 mm, 10 mm, 7.5 mm and 5 mm were used (SSD 80 cm). The machine-specific reference field fmsr was defined by the 60 mm collimator. A complete description of this treatment system is given in Kilby et al ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1177/153303461000900502”, “ISBN” : “1533-0338 (Electronic)\r1533-0338 (Linking)”, “ISSN” : “15330346”, “PMID” : “20815415”, “abstract” : “This review provides a complete technical description of the CyberKnife VSI System, the latest addition to the CyberKnife product family, which was released in September 2009. This review updates the previous technical reviews of the original system version published in the late 1990s. Technical developments over the last decade have impacted virtually every aspect of the CyberKnife System. These developments have increased the geometric accuracy of the system and have enhanced the dosimetric accuracy and quality of treatment, with advanced inverse treatment planning algorithms, rapid Monte Carlo dose calculation, and post-processing tools that allow trade-offs between treatment efficiency and dosimetric quality to be explored. This review provides a system overview with detailed descriptions of key subsystems. A detailed review of studies of geometric accuracy is also included, reporting a wide range of experiments involving phantom tests and patient data. Finally, the relationship between technical developments and the greatly increased range of clinical applications they have allowed is reviewed briefly.”, “author” : { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Dooley”, “given” : “J. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kuduvalli”, “given” : “G.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Sayeh”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Maurer”, “given” : “C. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Technology in Cancer Research and Treatment”, “id” : “ITEM-1”, “issue” : “5”, “issued” : { “date-parts” : “2010” }, “page” : “433-452”, “title” : “The CyberKnifeu00ae robotic radiosurgery system in 2010”, “type” : “article-journal”, “volume” : “9” }, “uris” : “http://www.mendeley.com/documents/?uuid=18764ae1-a9fe-4bf4-9c91-9feeae2881ba” } , “mendeley” : { “formattedCitation” : “<sup>38</sup>”, “plainTextFormattedCitation” : “38”, “previouslyFormattedCitation” : “<sup>38</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }38. OF measurements were performed at an SDD of 80 cm, with the detectors positioned at a depth of 1.5 cm in the water phantom.

II.B.1. Measuring protocols and Data analysis
OF measurements were accomplished for all the field sizes previously discussed. Measured OF values were defined as ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/59/19/5937”, “ISBN” : “1361-6560 (Electronic)\r0031-9155 (Linking)”, “ISSN” : “1361-6560”, “PMID” : “25210930”, “abstract” : “The purpose of this study was to derive a complete set of correction and perturbation factors for output factors (OF) and dose profiles. Modern small field detectors were investigated including a plastic scintillator (Exradin W1, SI), a liquid ionization chamber (microLion 31018, PTW), an unshielded diode (Exradin D1V, SI) and a synthetic diamond (microDiamond 60019, PTW). A Monte Carlo (MC) beam model was commissioned for use in small fields following two commissioning procedures: (1) using intermediate and moderately small fields (down to 2u00a0u00d7u00a02u00a0cm(2)) and (2) using only small fields (0.5u00a0u00d7u00a00.5u00a0cm(2)u00a0-2u00a0u00d7u00a02u00a0cm(2)). In the latter case the detectors were explicitly modelled in the dose calculation. The commissioned model was used to derive the correction and perturbation factors with respect to a small point in water as suggested by the Alfonso formalism. In MC calculations the design of two detectors was modified in order to minimize or eliminate the corrections needed. The results of this study indicate that a commissioning process using large fields does not lead to an accurate estimation of the source size, even if a 2u00a0u00d7u00a02u00a0cm(2) field is included. Furthermore, the detector should be explicitly modelled in the calculations. On the output factors, the scintillator W1 needed the smallest correction (+0.6%), followed by the microDiamond (+1.3%). Larger corrections were observed for the microLion (+2.4%) and diode D1V (-2.4%). On the profiles, significant corrections were observed out of the field on the gradient and tail regions. The scintillator needed the smallest corrections (-4%), followed by the microDiamond (-11%), diode D1V (+13%) and microLion (-15%). The major perturbations reported were due to volume averaging and high density materials that surround the active volumes. These effects presented opposite trends in both OF and profiles. By decreasing the radius of the microLion to 0.85u00a0mm we could modify the volume averaging effect in order to achieve a discrepancy less than 1% for OF and 5% for profiles compared to water. Similar results were observed for the diode D1V if the radius was increased to 1u00a0mm.”, “author” : { “dropping-particle” : “”, “family” : “Papaconstadopoulos”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Tessier”, “given” : “F”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in medicine and biology U6 – ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=On+the+correction%2C+perturbation+and+modification+”, “id” : “ITEM-1”, “issue” : “19”, “issued” : { “date-parts” : “2014” }, “page” : “5937”, “title” : “On the correction, perturbation and modification of small field detectors in relative dosimetry”, “type” : “article-journal”, “volume” : “59” }, “uris” : “http://www.mendeley.com/documents/?uuid=321fc159-eee6-4b54-ac03-84e57d54267c” } , “mendeley” : { “formattedCitation” : “<sup>28</sup>”, “plainTextFormattedCitation” : “28”, “previouslyFormattedCitation” : “<sup>28</sup>” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }28,ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4938584”, “ISSN” : “00942405”, “PMID” : “26745934”, “abstract” : “Purpose: The use of radiotherapy fields smaller than 3 cm in diameter has resulted in the need for accurate detector correction factors for small field dosimetry. However, published factors do not always agree and errors introduced by biased reference detectors, inaccurate Monte Carlo models, or experimental errors can be difficult to distinguish. The aim of this study was to provide a robust set of detector-correction factors for a range of detectors using numerical, empirical, and semiempirical techniques under the same conditions and to examine the consistency of these factors between techniques. Methods: Empirical detector correction factors were derived based on small field output factor measurements for circular field sizes from 3.1 to 0.3 cm in diameter performed with a 6 MV beam. A PTW 60019 microDiamond detector was used as the reference dosimeter. Numerical detector correction factors for the same fields were derived based on calculations from a geant4 Monte Carlo model of the detectors and the Linac treatment head. Semiempirical detector correction factors were derived from the empirical output factors and the numerical dose-to-water calculations. Results: The PTW 60019 microDiamond was found to over-respond at small field sizes resulting in a bias in the empirical detector correction factors. The over-response was similar in magnitude to that of the unshielded diode. Good agreement was generally found between semiempirical and numerical detector correction factors except for the PTW 60016 Diode P, where the numerical values showed a greater over-response than the semiempirical values by a factor of 3.7% for a 1.1 cm diameter field and higher for smaller fields. Conclusions: Detector correction factors based solely on empirical measurement or numerical calculation are subject to potential bias. A semiempirical approach, combining both empirical and numerical data, provided the most reliable results.”, “author” : { “dropping-particle” : “”, “family” : “O’Brien”, “given” : “Daniel J”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Leu00f3n-Vintru00f3”, “given” : “Luis”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “McClean”, “given” : “Brendan”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “1”, “issued” : { “date-parts” : “2016” }, “page” : “411”, “title” : “Small field detector correction factors kQclin, Qmsrfclin, fmsr for silicon-diode and diamond detectors with circular 6 MV fields derived using both empirical and numerical methods”, “type” : “article-journal”, “volume” : “43” }, “uris” : “http://www.mendeley.com/documents/?uuid=8447303d-dd21-4b6b-87d7-0322437ce855” } , “mendeley” : { “formattedCitation” : “;sup;30;/sup;”, “plainTextFormattedCitation” : “30”, “previouslyFormattedCitation” : “;sup;30;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }30 :
(1)
Where and are the detector readings for the fclin and the fmsr fields respectively. and f and Q are the collimator size in millimeters and the beam quality. The suffixes clin and msr represent the field of interest (clinical field) and the machine-specific reference (60 mm for a CyberKnife system), respectively ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.3005481”, “ISBN” : “0094-2405 (Print)”, “ISSN” : “00942405”, “PMID” : “19070252”, “abstract” : “The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.”, “author” : { “dropping-particle” : “”, “family” : “Alfonso”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Capote”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huq”, “given” : “M. Saiful”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kju00e4ll”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mackie”, “given” : “T. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ullrich”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vatnitsky”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “11”, “issued” : { “date-parts” : “2008” }, “page” : “5179-5186”, “title” : “A new formalism for reference dosimetry of small and nonstandard fields”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=727fa668-ab3f-4623-82d7-412c8121e6ac” } , “mendeley” : { “formattedCitation” : “;sup;1;/sup;”, “plainTextFormattedCitation” : “1”, “previouslyFormattedCitation” : “;sup;1;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }1. The approach taken consisted of performing a measurement with the reference cone (60 mm) before and after the measurements with the cones of interest (5–50 mm).

Each detector reading represents the average of five consecutive measurements, obtained after 100 MU irradiation steps. As for the measured OF values were corrected in order to take into account the dose per pulse dependence of the device response, as reported by the manufacturer (PTW 2017). In this respect, it is worth to point out that the applied correction factors were below 1% for all the measured OFs.

The field factors were then determined as:
(2)
according to the formalism introduced by ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.3005481”, “ISBN” : “0094-2405 (Print)”, “ISSN” : “00942405”, “PMID” : “19070252”, “abstract” : “The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.”, “author” : { “dropping-particle” : “”, “family” : “Alfonso”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Andreo”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Capote”, “given” : “R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Huq”, “given” : “M. Saiful”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kju00e4ll”, “given” : “P.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Mackie”, “given” : “T. R.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Palmans”, “given” : “H.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Rosser”, “given” : “K.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Seuntjens”, “given” : “J.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Ullrich”, “given” : “W.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Vatnitsky”, “given” : “S.”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “11”, “issued” : { “date-parts” : “2008” }, “page” : “5179-5186”, “title” : “A new formalism for reference dosimetry of small and nonstandard fields”, “type” : “article-journal”, “volume” : “35” }, “uris” : “http://www.mendeley.com/documents/?uuid=727fa668-ab3f-4623-82d7-412c8121e6ac” } , “mendeley” : { “formattedCitation” : “;sup;1;/sup;”, “plainTextFormattedCitation” : “1”, “previouslyFormattedCitation” : “;sup;1;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }1, by using the OFs defined in equation (1) and the correction factors obtained by MC calculation.

II.B.2. Uncertainty evaluation
The uncertainty in the output factor measurements was evaluated, according to the IAEA TRS-398 dosimetry protocol ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1097/00004032-200111000-00017”, “ISBN” : “978-92-0-105807”, “ISSN” : “00179078”, “abstract” : “In its Report 24 on u2018Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotherapy Proceduresu2019, the International Commission on Radiation Units and Measurements (ICRU) 1 concluded that u201calthough it is too early to generalize, the available evidence for certain types of tumour points to the need for an accuracy of u00b15% in the delivery of an absorbed dose to a target volume if the eradication of the primary tumour is soughtu201d. The ICRU continues, u201cSome clinicians have requested even closer limits such as u00b12%, but at the present time (in 1976) it is virtually impossible to achieve such a standardu201d. These statements were made in a context where uncertainties were estimated at the 95% confidence level, and have been interpreted as if they correspond to approximately two standard deviations. Thus the requirement for an accuracy of 5% in the delivery of absorbed dose would correspond to a combined uncertainty of 2.5% at the level of one standard deviation. Today it is considered that a goal in dose delivery to the patient based on such an accuracy requirement is too strict and the figure should be increased to about one standard deviation of 5%, but there are no definite recommendations in this respect.1 The requirement for an accuracy of u00b15% could, on the other hand, also be interpreted as a tolerance of the deviation between the prescribed dose and the dose delivered to the target volume. Modern radiotherapy has confirmed, in any case, the need for high accuracy in dose delivery if new techniques, including dose escalation in 3-D conformal radiotherapy, are to be applied. Emerging technologies in radiotherapy, for example modern diagnostic tools for the determination of the target volume, 3-D commercial treatment planning systems and advanced accelerators for irradiation, can only be fully utilized if there is high accuracy in dose determination and delivery.”, “author” : { “dropping-particle” : “”, “family” : “International Atomic Energy Agency”, “given” : “”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Atomic Energy”, “id” : “ITEM-1”, “issued” : { “date-parts” : “2000” }, “page” : “1-229”, “title” : “IAEA Technical Report Series No.398”, “type” : “article-journal” }, “uris” : “http://www.mendeley.com/documents/?uuid=68dc37fd-7129-4e09-a06b-eea7d08e2749” } , “mendeley” : { “formattedCitation” : “;sup;39;/sup;”, “plainTextFormattedCitation” : “39”, “previouslyFormattedCitation” : “;sup;39;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }39 combining two different contributions: establishment of the measurement conditions (0.4%, 1 standard deviation, SD) and dosimeter reading relative to beam monitor (0.6%, 1 SD). These values are quoted in the same IAEA protocol as well. Hence, a global uncertainty in the OF ratio of 1% (1 SD) is estimated. This evaluation does not take into account possible effects coming from the unsuitable spatial resolution of the detector and from the difficulty of a correct detector positioning in narrow fields.

Results
III. A. Measurements with microdiamond (MD)
In graph (1) a comparison between OF measurements of MicroDiamond detector and FF after using correction factors reported in ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/1361-6560/aa7e59”, “ISSN” : “13616560”, “abstract” : “u00a9 2017 Institute of Physics and Engineering in Medicine. A systematic study of the PTW microDiamond (MD) output factors (OF) is reported, aimed at clarifying its response in small fields and investigating its suitability for small field reference dosime try. Ten MDs were calibrated under 60 Co irradiation. OF measurements were performed in 6 MV photon beams by a CyberKnife M6, a Varian DHX and an Elekta Synergy linacs. Two PTW silicon diodes E (Si-D) were used for comparison. The results obtained by the MDs were evaluated in terms of absorbed dose to water determination in reference conditions and OF measurements, and compared to the results reported in the recent literature. To this purpose, the Monte Carlo (MC) beam-quality correction factor, , was calculated for the MD, and the small field output correction factors, , were calculated for both the MD and the Si-D by two different research groups. An empirical function was also derived, providing output correction factors within 0.5% from the MC values calculated for all of the three linacs. A high reproducibility of the dosimetric properties was observed among the ten MDs. The experimental values are in agreement within 1% with the MC calculated ones. Output correction factors within +0.7% and -1.4% were obtained down to field sizes as narrow as 5 mm. The resulting MD and Si-D field factors are in agreement within 0.2% in the case of CyberKnife measurements and 1.6% in the other cases. This latter higher spread of the data was demonstrated to be due to a lower reproducibility of small beam sizes defined by jaws or multi leaf collimators. The results of the present study demonstrate the reproducibility of the MD response and provide a validation of the MC modelling of this device. In principle, accurate reference dosimetry is thus feasible by using the microDiamond dosimeter for field sizes down to 5 mm.”, “author” : { “dropping-particle” : “”, “family” : “Coste”, “given” : “Vanessa”, “non-dropping-particle” : “De”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Francescon”, “given” : “Paolo”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Marinelli”, “given” : “Marco”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Masi”, “given” : “Laura”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Paganini”, “given” : “Lucia”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Pimpinella”, “given” : “Maria”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Prestopino”, “given” : “Giuseppe”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Russo”, “given” : “Serenella”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Stravato”, “given” : “Antonella”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona”, “given” : “Claudio”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Verona-Rinati”, “given” : “Gianluca”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in Medicine and Biology”, “id” : “ITEM-1”, “issue” : “17”, “issued” : { “date-parts” : “2017” }, “page” : “7036-7055”, “publisher” : “IOP Publishing”, “title” : “Is the PTW 60019 microDiamond a suitable candidate for small field reference dosimetry?”, “type” : “article-journal”, “volume” : “62” }, “uris” : “http://www.mendeley.com/documents/?uuid=872081b0-5d99-4c0b-9570-4e2cec91477c” } , “mendeley” : { “formattedCitation” : “;sup;40;/sup;”, “plainTextFormattedCitation” : “40”, “previouslyFormattedCitation” : “;sup;40;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }40 the graph displayed that the output factor using microdiamond before and after using correction is the same. That means the microdiamond is a good candidate for dosemitry of small field

Phys. Med. Biol. 62 (2017) 7036–7055

Fig. (1). Comparison between OF (Output Factor) and FF (Field Factor) in MicroDiamond (MD) detector.

III.B. Measurements with Liquidfilled microchamber PTW 31018 microLion
In graph (2) a comparison between OF measurements of Microlion detector and FF after using correction factors reported in ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1088/0031-9155/57/12/3741”, “ISBN” : “0031-9155”, “ISSN” : “0031-9155”, “PMID” : “22617842”, “abstract” : “Monte Carlo (MC) simulation of dose to water and dose to detector has been used to calculate the correction factors needed for dose calibration and output factor measurements on the CyberKnife system. Reference field ionization chambers simulated were the PTW 30006, Exradin A12, and NE 2571 Farmer chambers, and small volume chambers PTW 31014 and 31010. Correction factors for Farmer chambers were found to be 0.7%u20130.9% larger than those determined from TRS-398 due mainly to the dose gradient across the chamber cavity. For one microchamber where comparison was possible, the factor was 0.5% lower than TRS-398 which is consistent with previous MC simulations of flattening filter free Linacs. Output factor detectors simulated were diode models PTW 60008, 60012, 60017, 60018, Sun Nuclear edge detector, air-filled microchambers Exradin A16 and PTW 31014, and liquid-filled microchamber PTW 31018 microLion. Factors were generated for both fixed and iris collimators. The resulting correction factors differ from unity by up to +11% for air-filled microchambers and u22126% for diodes at the smallest field size (5 mm), and tend towards unity with increasing field size (correction factor magnitude 15 mm). Output factor measurements performed using these detectors with fixed and iris collimators on two different CyberKnife systems showed initial differences between detectors of ;15% at 5 mm field size. After correction the measurements on each unit agreed within u223c1.5% at the smallest field size. This paper provides a complete set of correction factors needed to apply a new small field dosimetry formalism to both collimator types on the CyberKnife system using a range of commonly used detectors.”, “author” : { “dropping-particle” : “”, “family” : “Francescon”, “given” : “P”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Kilby”, “given” : “W”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Satariano”, “given” : “N”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Cora”, “given” : “S”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Physics in Medicine and Biology”, “id” : “ITEM-1”, “issue” : “12”, “issued” : { “date-parts” : “2012” }, “page” : “3741-3758”, “title” : “Monte Carlo simulated correction factors for machine specific reference field dose calibration and output factor measurement using fixed and iris collimators on the CyberKnife system”, “type” : “article-journal”, “volume” : “57” }, “uris” : “http://www.mendeley.com/documents/?uuid=fdbafa99-ae2d-49f6-b9a5-cf06c4d7e714” } , “mendeley” : { “formattedCitation” : “;sup;41;/sup;”, “plainTextFormattedCitation” : “41”, “previouslyFormattedCitation” : “;sup;41;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }41 , the microLion measured values agreed with Monte Carlo results for all the cones except the 5-mm cone, for which under responses were evident.

Phys. Med. Biol. 57 (2012) 3741–3758

Fig. (2). Comparison between OF (Output Factor) and FF (Field Factor) in MicroLion (ML) detector.

III. C. Measurements with PTW 60018 Diode
The silicon diodes agreed within 1% of the calculated total scatter factors for cones with a diameter of 20 mm or greater without any correction factor. Silicon diodes are widely used for radiosurgery system commissioning and QA measurements, thereby resulting in a slightly lower actual dose delivered to the patient for the smallest cones than that predicted by the planning system when no correction factor is applied to the
measurements.

Insert Diode graph and correction table
Fig. (3). Comparison between OF (Output Factor) and FF (Field Factor) in Diode detector.

The PTW 60018 silicon diode rendered the worst results with noticeable over-response for cones smaller than 20 mm in diameter. All the silicon diodes over-responded compared with Araki’s calculated values in small fieldsADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.2219774”, “ISSN” : “00942405”, “author” : { “dropping-particle” : “”, “family” : “Araki”, “given” : “Fujio”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical Physics”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2006”, “7”, “26” }, “page” : “2955-2963”, “publisher” : “American Association of Physicists in Medicine”, “title” : “Monte Carlo study of a Cyberknife stereotactic radiosurgery system”, “type” : “article-journal”, “volume” : “33” }, “uris” : “http://www.mendeley.com/documents/?uuid=02f9cb87-a5a9-34ed-9ac6-9b03279c4c0d” } , “mendeley” : { “formattedCitation” : “;sup;5;/sup;”, “plainTextFormattedCitation” : “5”, “previouslyFormattedCitation” : “;sup;5;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }5.

Comparison between Microdiamond (MD) and MicroLion (ML) in OF and FF.III.D. Measurements with PSD
The measured Output factors using the PSDs showed very good agreement, with those calculated in two different Monte Carlo studies mentioned before.
Insert PSD graph and correction table
Fig. (4). Comparison between OF (Output Factor) and FF (Field Factor) in PSD detector.

Discussions
A recent Monte Carlo study suggested that the over responses of the microLion (ML) in small fields arose from the high density material surrounding the sensitive volume. ADDIN CSL_CITATION { “citationItems” : { “id” : “ITEM-1”, “itemData” : { “DOI” : “10.1118/1.4812687”, “ISBN” : “0094-2405”, “ISSN” : “0094-2405”, “PMID” : “23927339”, “abstract” : “PURPOSE: The Alfonso et al. Med. Phys. 35, 5179-5186 (2008) formalism for small field dosimetry proposes a set of correction factors (kQclin,Qmsrfclin,fmsr) which account for differences between the detector response in nonstandard (clinical) and machine-specific-reference fields. In this study, the Monte Carlo method was used to investigate the viability of such small field correction factors for four different detectors irradiated under a variety of conditions. Because kQclin,Qmsrfclin,fmsr values for single detector position measurements are influenced by several factors, a new theoretical formalism for integrated-detector-position dose area product (DAP) measurements is also presented and was tested using Monte Carlo simulations.\n\nMETHODS: A BEAMnrc linac model was built and validated for a Varian Clinac iX accelerator. Using the egs++ geometry package, detailed virtual models were built for four different detectors: a PTW 60012 unshielded diode, a PTW 60003 Diamond detector, a PTW 31006 PinPoint (ionization chamber), and a PTW 31018 MicroLion (liquid-filled ionization chamber). The egs_chamber code was used to investigate the variation of kQclin,Qmsrfclin,fmsr with detector type, detector construction, field size, off-axis position, and the azimuthal angle between the detector and beam axis. Simulations were also used to consider the DAP obtained by each detector: virtual detectors and water voxels were scanned through high resolution grids of positions extending far beyond the boundaries of the fields under consideration.\n\nRESULTS: For each detector, the correction factor (kQclin,Qmsrfclin,fmsr) was shown to depend strongly on detector off-axis position and detector azimuthal angle in addition to field size. In line with previous studies, substantial interdetector variation was also observed. However, it was demonstrated that by considering DAPs rather than single-detector-position dose measurements the high level of interdetector variation could be eliminated. Under small field conditions, mass density was found to be the principal determinant of water equivalence. Additionally, the mass densities of components outside the sensitive volumes were found to influence the detector response.\n\nCONCLUSIONS: kQclin,Qmsrfclin,fmsr values for existing detector designs depend on a host of variables and their calculation typically relies on the use of time-intensive Monte Carlo methods. Future moves toward density-compensated detector designs or DAu2026”, “author” : { “dropping-particle” : “”, “family” : “Underwood”, “given” : “T S a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Winter”, “given” : “H C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hill”, “given” : “M a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fenwick”, “given” : “J D”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Carlo”, “given” : “Monte”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Underwood”, “given” : “T S a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Winter”, “given” : “H C”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Hill”, “given” : “M a”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” }, { “dropping-particle” : “”, “family” : “Fenwick”, “given” : “J D”, “non-dropping-particle” : “”, “parse-names” : false, “suffix” : “” } , “container-title” : “Medical physics”, “id” : “ITEM-1”, “issue” : “8”, “issued” : { “date-parts” : “2013” }, “page” : “082102”, “title” : “Detector density and small field dosimetry: integral versus point dose measurement schemes.”, “type” : “article-journal”, “volume” : “40” }, “uris” : “http://www.mendeley.com/documents/?uuid=4a0731b1-a214-4d4d-b21e-4f98c35211e0” } , “mendeley” : { “formattedCitation” : “;sup;12;/sup;”, “plainTextFormattedCitation” : “12”, “previouslyFormattedCitation” : “;sup;12;/sup;” }, “properties” : { “noteIndex” : 0 }, “schema” : “https://github.com/citation-style-language/schema/raw/master/csl-citation.json” }12. MicroLion is good radiosurgery detectors but should be used carefully with the smallest fields because of the associated volume-averaging and perturbation effects. We compared several stereotactic detectors by measuring Output factors and Field factors. Currently available commercial detectors have limitations to perform accurate small field dosimetry (?20 mm), and these limitations have been observed in the present study. We showed herein that silicon diodes are water nonequivalent. However, their water nonequivalence causes over-responses in the tails of the larger fields available using a CyberKnife system. Moreover, important overestimations of the Output factors have been observed in small fields (<10 mm) with silicon diodes.

The microLion under responded to about 2.5% with the 5 mm cone because of a compensation for a volume averaging effect and an over response caused by the surrounding high density material. Our findings show that small field output factors can be accurately measured using water equivalent dosimeters like PSDs, which provided results similar to those of two independent Monte Carlo studies. PSDs are good candidates for reference radiosurgery detectors for measurements requiring water equivalence, such as total scatter factors, tissue phantom ratios, percent depth doses, and total treatment delivery verification.

The microDiamond PTW60019 is a suitable detector for commissioning and routine use of Gamma Knife with good agreement of both DORs and profiles in the three directions. The measurements reported in the present work confirm the suitability of natural diamond detector for clinical dosimetry. There are some drawbacks to be considered in the use of diamond detector, among which (1) Signal shows a dose rate dependence that must be accounted for in order to obtain correct dose distributions, while the results here reported excluding such dependence for silicon; (2) it is less user friendly, since it necessitates a pre-irradiation dose, before daily use, to stabilize the response, and (3) it has a slow response in time, needing up to about 2 s to obtain signal stability (this value has been obtained in the frame work of a detailed study of the response dynamic, currently under way by some of the authors). Also, the relative high acquiring cost, compared to that of the other dosimeters here studied, should be considered in a pros and cons balance.

Considering the previous mentioned drawbacks and the small differences in OF, penumbra and field width evaluations, in the range of field sizes investigated, there is not relevant advantage in the use of diamond detector with respect to silicon diode for routine use in clinical applications. With special radiotherapy techniques, such as intensity modulated radiation therapy or stereotactic treatments, where field sizes smaller than 2.6 cm32.6 cm are employed, the independence of response with energy is a major request. In these cases diamond detector might be appreciably superior to silicon diode due to its tissue equivalence. This property was of minor importance in the present work, since it led to a significant difference for PDD determination only in the distal region.

Conclusion
We conclude that the four detectors exhibit good candidate for collimator field size ?20mm but for smaller fields (<10 mm), each dosimeter type exhibited different behaviors; The silicon diodes over-responded because of their water nonequivalence; the microLion and Eradin W1 Scintillator ( PSD) was the only detector within the uncertainties of the Monte Carlo simulations for all the cones. The results prove the reproducibility of the MD and MicroLion response and afford a validation of those detectors in small field dosimetry. In principle, accurate reference dosimetry is thus viable by using the microDiamond and MicroLion dosimeter for field sizes down to 5 mm.

ACKNOWLEDGMENTS
Kindly I want to acknowledge support from the ICTP/IAEA STEP programme for acceptance me and help me to take this chance to complete my PhD work. Additionally, I cannot express enough thanks for both Prof. Francescon and Dr. Nenvia. My completion of this project could not have been accomplished without the continued support of them. Finally, I offer my sincere appreciation for all Medical Physics group members in San Bortolo hospital.

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