Validation of BEAMnrc Monte Carlo model for a 12 MV photon beam

Abstract

Accurate dose calculation in the treatment planning system (TPS) process is the most important step to succeed the radiation therapy. For this purpose, Monte Carlo method is a powerful tool for dose calculation. This study aims to validate Monte Carlo BEAMnrc model of Saturne43 Linac head to simulate 12 MV photon beam. To validate MC model, the dose distributions were calculated by BEAMnrc simulation and then the results obtained were compared against measurements. This requires to adjust the parameters of the initial electron beam incident on the target, such as mean energy, beam radius and mean angular spread. Our approach has been suggested to determine the initial electron beam parameters. The dose distribution (percent depth dose and lateral profile) has been calculated for 10 × 10 cm2 field size in a homogeneous water phantom of 40 × 40 × 40 cm3. The results obtained are compared with measured data using gamma index criteria which were fixed within 1.5%-1 mm accuracy. Using phase space technique as a sub-source allows us to reduce the simulation time by a factor of 6. Good agreement between calculated and measured dose has been achieved when the mean energy, beam width and mean angular spread were 11.8 MeV, 1.5 mm and 0.5°, respectively. So, Monte Carlo based- BEAMnrc code is suitable to be used in the process of treatment planning system for calculating dose distribution. Keywords: Monte Carlo, BEAMnrc, Dose distribution, Linac, Phase space