Small fields output factors measurements and correction factors determination for several detectors for a CyberKnife<sup>®</sup> and linear accelerators equipped with microMLC and circular cones

Bassinet, C.; Huet, C.; Derreumaux, S.; Brunet, Guy; Chea, M.; Baumann, M.; Lacornerie, T.; Gaudaire-Josset, S.; Trompier, F.; Roch, P.; Boisserie, G.; Clairand, I.

doi:10.1118/1.4811139

Cited by 133 publications

(159 citation statements)

References 30 publications

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“…In both the cases, the detectors were used in the 5 mm cone fields and 10 × 10 cm fields. In one case, a correction factor was applied from Bassinet et al., 8 and in the other case, no correction was applied. The standard deviation of the two results was 3.9% and the average was 0.649.…”

Section: Resultsmentioning

confidence: 99%

Survey of 5 mm small‐field output factor measurements in Australia

Oliver¹,

Butler²,

Takau³

et al. 2018

J Applied Clin Med Phys

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The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison exercise in April 2016 where participants came to ARPANSA and measured the output factor of a nominal 5 mm cone attached to the ARPANSA Elekta Synergy (Elekta, Crawley, UK) linear accelerator. The goal of the exercise was to compare the consistency and methods used by independent medical physicists in measuring small‐field output factors. ARPANSA provided a three‐dimensional scanning tank for detector setup and positioning, but the participants were required to measure the output factor with their own detectors. No information regarding output factors previously measured was supplied to participants to make each result as independent as possible. Fifteen groups travelled to ARPANSA bringing a wide range of detectors and methods. A total of 30 measurements of the output factor were made. The standard deviation of the measurements (excluding one expected outlier from an uncorrected ionization chamber measurement) was 3.6%. The results provide an insight into the consistency of small‐field dosimetry being performed in Australia and New Zealand at the present time.

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Section: Resultsmentioning

confidence: 99%

Survey of 5 mm small‐field output factor measurements in Australia

Oliver¹,

Butler²,

Takau³

et al. 2018

J Applied Clin Med Phys

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“…Small fields formed by MLC leaves are common in IMRT/VMAT plans, but the dosimetry of small fields has been one of the biggest challenges in radiation therapy, especially for irregularly shaped fields, which are common in IMRT/VMAT plans 16 , 17 . The dose measurement of small fields is subject to the ion chamber volume effect, stem effect, leaking, and other effects, and the analytical dose calculation algorithm for small fields is subject to the lateral electron nonequilibrium and penumbra, in addition to those inputs from measurements.…”

Section: Introductionmentioning

confidence: 99%

Determining the optimal dosimetric leaf gap setting for rounded leaf‐end multileaf collimator systems by simple test fields

Yao

Farr

2015

J Applied Clin Med Phys

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Individual QA for IMRT/VMAT plans is required by protocols. Sometimes plans cannot pass the institute's QA criteria. For the Eclipse treatment planning system (TPS) with rounded leaf‐end multileaf collimator (MLC), one practical way to improve the agreement of planned and delivered doses is to tune the value of dosimetric leaf gap (DLG) in the TPS from the measured DLG. We propose that this step may be necessary due to the complexity of the MLC system, including dosimetry of small fields and the tongue‐and‐groove (T&G) effects, and report our use of test fields to obtain linac‐specific optimal DLGs in TPSs. More than 20 original patient plans were reoptimized with the linac‐specific optimal DLG value. We examined the distribution of gaps and T&G extensions in typical patient plans and the effect of using the optimal DLG on the distribution. The QA pass rate of patient plans using the optimal DLG was investigated. The dose‐volume histograms (DVHs) of targets and organs at risk were checked. We tested three MLC systems (Varian millennium 120 MLC, high‐definition 120 MLC, and Siemens 160 MLC) installed in four Varian linear accelerators (linacs) (TrueBEAM STx, Trilogy, Clinac 2300 iX, and Clinac 21 EX) and 1 Siemens linac (Artiste). With an optimal DLG, the individual QA for all those patient plans passed the institute's criteria (95% in DTA test or gamma test with 3%/3 mm/10%), even though most of these plans had failed to pass QA when using original DLGs optimized from typical patient plans or from the optimization process (automodeler) of Pinnacle TPS. Using either our optimal DLG or one optimized from typical patient plans or from the Pinnacle optimization process yielded similar DVHs.PACS number: 87.55Qr

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“…In case of small beams, the fraction of photons scattered from parts of the detector is higher compared with the case of large beams, possibly resulting in an overestimation of the OF. Considering a 7% overresponse of the EDGE detector, as reported by Bassinet et al 44 for the 6 3 6-mm 2 field of a Clinac 2100 equipped with additional micro-MLC, the differences between W1 PSD and the corrected EDGE diode are reduced to roughly 4 and 10% for 8 3 8-and 6 3 6-mm 2 field sizes, respectively.…”

Section: 4mentioning

confidence: 99%

Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector

Pasquino

Cutaia

Radici

et al. 2017

BJR

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Objective: The aim of this work was to investigate the main dosimetric characteristics and the performance of an A26 Exradin ionization microchamber (A26 IC) and a W1 Exradin plastic scintillation detector (W1 PSD) in small photon beam dosimetry for treatment planning system commissioning and quality assurance programme. Methods: Detector characterization measurements (short-term stability, dose linearity, angular dependence and energy dependence) were performed in water for field sizes up to 10 3 10 cm 2 . Polarity effect (P pol ) was examined for the A26 IC. The behaviour of the detectors in small field relative dosimetry [percentage depth dose, dose profiles often called the off-axis ratio and output factors (OFs)] was investigated for field sizes ranging from 1 3 1 to 3 3 3 cm 2 . Results: Results were compared with those obtained with other detectors we already use for small photon beam dosimetry. A26 IC and W1 PSD showed a linear dose response. While the A26 IC showed no energy dependence, the W1 PSD showed energy dependence within 2%; no angular dependence was registered. P pol values for A26 IC were below 0.9% (0.5% for field size .2 3 2 cm 2 ). A26 IC and W1 PSD depth-dose curves and lateral profiles agreed with those obtained with an EDGE diode. No differences were observed among the detectors in OF measurement for field sizes larger than 1 3 1 cm 2 , with average differences ,1%. For field sizes ,1 3 1 cm 2 , the effective volume of ionization chamber and non-water equivalence of EDGE diode become significant. A26 IC OF values were significantly lower than EDGE diode and W1 PSD values, with percentage differences of about 223 and 213% for the smallest field, respectively. W1 PSD OF values lay between ion chambers and diode values, with a maximum percentage difference of about 210% with respect to the EDGE diode, for a 6 3 6-mm 2 field size. Conclusion: The results of our investigation confirm that A26 IC and W1 PSD could play an important role in small field relative dosimetry. Advances in knowledge: Dosimetric characteristics of Exradin A26 ionization microchamber and W1 plastic scintillation detector for small field dosimetry.

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Small fields output factors measurements and correction factors determination for several detectors for a CyberKnife^® and linear accelerators equipped with microMLC and circular cones

Cited by 133 publications

References 30 publications

Survey of 5 mm small‐field output factor measurements in Australia

Survey of 5 mm small‐field output factor measurements in Australia

Determining the optimal dosimetric leaf gap setting for rounded leaf‐end multileaf collimator systems by simple test fields

Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector

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Small fields output factors measurements and correction factors determination for several detectors for a CyberKnife® and linear accelerators equipped with microMLC and circular cones

Cited by 133 publications

References 30 publications

Survey of 5 mm small‐field output factor measurements in Australia

Survey of 5 mm small‐field output factor measurements in Australia

Determining the optimal dosimetric leaf gap setting for rounded leaf‐end multileaf collimator systems by simple test fields

Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector

Contact Info

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Small fields output factors measurements and correction factors determination for several detectors for a CyberKnife^® and linear accelerators equipped with microMLC and circular cones