Program Information
Determination of Small MLC-Fields Corrections Factors for Several Detectors Using Monte-Carlo Simulations and EBT3 Gafchromic Films
T Younes1, 2, 3 *, L Simon1, 2 , M Chauvin1, G Fares3 , L Vieillevigne1, 2 , (1) Cancer Research Center of Toulouse, UMR1037 INSERM - University Toulouse 3 - ERL5294 CNRS, 2 avenue Hubert Curien, Oncopole de Toulouse, 31037 Toulouse Cedex 1, France (2) Cancer University Institut of Toulouse, 1 avenue Irene Joliot Curie, 31059 Toulouse Cedex 9, France (3) University Saint-Joseph of Beyrouth, Faculty of Sciences, Campus of Science and Technology, Mar Roukos - Dekwaneh, Lebanon
Presentations
SU-F-108-4 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 108
Purpose: This study aimed to determine a set of correction factors (CFs) for the PTW-60019 microdiamond, the PTW-60017 Ediode, and the PTW-31016 and 31022 Pinpoint 3D chambers for small multi-leaf collimator (MLC) fields in water. Empirical and semi-empirical techniques were used to assess the degree of agreement between these two approaches. 6MV-flattening filter (6FF) and 6MV-flattening filter free (6FFF) beams were investigated. Two dosimetric algorithms, Acuros XB (AXB) and Anisotropic Analytical algorithm (AAA), implemented in Eclipse TPS were also evaluated for these cases.
Methods: Geant4 application for emission tomography (GATE) code was used to accurately model the TrueBeam STx accelerator equipped with HD120-MLC using confidential data provided by Varian¹. Small MLC-field output factors (OFs) ranging from 0.5×0.5 cm² to 3×3 cm² were generated for each detector. Their CFs² were calculated using GATE simulations and EBT3 Gafchromic film (GF) measurements. The microdiamond and Ediode measurements were normalized at a specific reference field of 3×3 cm².
Results: GATE OFs agreed within 0.3% with those of GF for all field sizes and energies. For MLC-fields under 1.5×1.5 cm², microdiamond and Ediode were found to over-respond whereas ionization chambers significantly underestimated the absorbed doses, compared to GATE and GF values. However, PTW-31022 required less significant CFs than PTW-31016. For all detectors, CFs were closer to unity for 6FFF beams than 6FF beams. AXB OFs differed no more than 1% from those of GATE for all MLC-fields except 0.5×0.5 cm², where it was underestimated by 5.2% and 3.5% for 6FF and 6FFF energies, respectively. For 6FF beams, the AAA calculated OF deviations ranged from 1.6% to 4.4% compared to GATE for MLC-fields under 2×2 cm².
Conclusion: The empirical and semi-empirical methods provided reliable results for the determination of detector CFs. Further studies on the MLC-field CFs for 10FFF energy are ongoing.
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