Benchmarking of Monte Carlo model of 6 Mv photon beam produced by Siemens Oncor® linear accelerator: determination of initial electron beam parameters in comparison with measurement

Introduction: The aim of this study was to investigate the initial electron beam parameters for Monte Carlo model of 6MV photon beam produced by Siemens Oncor® linear accelerator.   Materials and Methods: In this study, the EGSnrc Monte Carlo user codes BEAMnrc and DOSXYZnrc were used. The beamnrc code were used for modelling of a 6 MV photon beam produced by Siemens Oncor® linac’s head and DOSXYZnrc code utilized for calculating dose distributions in a virtual water phantom. The simulations were started for 10×10 cm2 and 40×40 cm2 field sizes. First the electron energy was changed to match percent depth dose curves of simulations with those of measurements. Second the beam width of primary electron source was tweaked to match between dose profile curves of simulation with those of measurement. For data comparison a 1-dimensional Gamma analyses were used with criteria of 3%/ 3mm using an inhouse-matlab script. The gamma analyses were performed while dose distributions of Monte Carlo and measurements were set as an evaluated and reference dose.   Results: The results of gamma analyses showed that for percent depth dose curves a passing rate of close to 100% evaluated points. Also for profile curves, the passing rates were above 95% of evaluated points. Therefore, all depth dose and dose profile curves were in good agreement. The agreements were found at 5.75 MeV primary electron and 0.35 cm beam width respectively.   Conclusion: The Monte Carlo model of 6 MV photon beam produced by Siemens Oncor® linear accelerator was accurately benchmarked using measured data. Since the profile curves of large field sizes are much more sensitive to the variations of beam width than small field size, it is recommended that for tuning process both field sizes are considered.