Abstract

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Title:: Comparison analysis of energy spectra between flattened and flattening-filter-free Monte Carlo models for photon beam

Author(s):: YUE Haizhen; ZHANG Yibao; ZHANG Jian; LIU Zhuolun; HU Qiaoqiao; JIANG Fan; WU Hao; Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiotherapy, Peking University Cancer Hospital & Institute, Beijing 100142, China

Keywords:: ; photon beam; flattened model; flattening-filter free model; Monte Carlo; energy spectrum

Abstract:: Objective To compare and analyze the energy spectra of 6 MV flattened and flattening-filter-free photon beam in the air medium and standard water phantom at specific depth. Methods BEAMnrc program was used to model Varian TrueBeam accelerator gantry head, including flattened model and flattening-filter-free model. The phase space files of (40×40) cm2 field at SSD of 110 cm in air medium and standard water phantom were calculated. The energy spectrum distribution in different regions of the irradiation field were compared and analyzed with the use of BEAMDP program. Results For the irradiation field of (40×40) cm2 at SSD of 110 cm in air medium, with the enlargement of statistical regions, the low energy part in the energy spectrum of flattened model increased, while that of flattening filter-free model decreased. For the standard water phantom at depth of 10 cm, large differences were found in the energy spectrum of two models with or without scatter, mainly in the area less than 0.511 MeV. The low energy part in the energy spectrum of flattened model in different locations decreased in crossplane direction, while the flattening filter-free model showed opposite trend. Compared with electron and position electron, the photon had great effects on the energy spectrum in the same irradiation field. Conclusion This study provides basis for further clinical dosimetric data measurement and calibration of medical linear accelerator.