Abstract

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Title:: Monte Carlo simulation and comparison for the penumbra characteristics of flattening filter and flattening filter free photon beams from medical electron linear accelerator

Author(s):: TANG Huanan1; CHEN Lei2; FU Yuchuan1; LI Changhu1; HAN Jifeng2; 1. Radiotherapy Physics & Technology Center/Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China 2. Key Laboratory of Radiation Physics and Technology, Ministry of Education/Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China

Keywords:: Keywords: flattening filter mode flattening filter free mode Monte Carlo simulation medical electron linear accelerator penumbra

Abstract:: Abstract: Objective To analyze the penumbral characteristics of flattening filter (FF) and flattening filter free (FFF) photon beams under different energy conditions using Monte Carlo simulation. Methods BEAMnrc program was used to model Elekta Versa HD accelerator head in FF mode and FFF mode, and DOSXYZnrc program to build the standard water tank model. The percentage depth dose (PDD) and off-axis ratio (OAR) of the photon beam in the standard water model under different modes and different incident electron energies were simulated and compared with the measurement data to determine the incident electron energy of the photon beam in different modes. For FF beam, the width between 20% and 80% of the beam center axis dose was used to calculate the penumbral and for FFF beam, the penumbral was calculated with Ponisch method. The penumbral widths of different beams were compared. Results With the same incident electron energy, the penumbra of 6 MV FFF beam was sharper than that of 6 MV FF beam, but the penumbra advantage of FFF beam gradually disappeared with the increase of the field size. When the incident electron energy was increased to 7.0 MeV, the penumbra of 6 MV FFF beam tended to coincide with that of 6 MV FF beam. For 10 MV FF and 10 MV FFF beams, FFF beam penumbra had obvious advantages for small filed. Conclusion Incident electron energy is the main factor determining the characteristics of different beam penumbras.