Monte Carlo Simulation of particle production in target material linac 15, 18, and 20 MV photon beam

Abstract

Target is one of the important components in a linear accelerator (linac). Target materials depend on the energy of linac so that they have different spectrums produced. This study investigates the spectrum characteristic of target material for some linacs using Monte Carlo codes. The target geometry and material simulated was collected from Varian Medical System. The simulation was carried out on two different Monte Carlo codes, namely PHITS and EGSnrc. In the simulation process, the cut-off energy of electron and photon are set in the same value at 0.521 MeV and 0.01 MeV, respectively. The SLAB geometry is implemented to model the target. The spectrum of photon and electron was collected at the end of the target. The deviation of electron and photon spectrum collected from PHITS and EGSnrc was calculated. The results show that the spectrum of photon and electron from PHITS and EGSnrc have the same trend with a deviation of more than 25%. The maximum differences between the codes were obtained at energy 0.04 MeV<E<0.3 MeV for 15 MeV sources. Differences between PHITS and EGSnrc are more than 17% in electron energy 18 and 20 MeV. The big deviation is caused by the cross-section data applied in PHITS and EGSnrc being different in some photon and electron interaction cross-sections.