Monte Carlo simulation of Electron Beams; Influential Parameters and Potential Sources of Simulation Faults

Abstract

High-energy photon and electron beams were accurately simulated by Monte Carlo code. Electron simulation is not easy due to their light weight and their scattering nature. Moreover, because of the commercial value of the detailed specifications of the accelerator parts, manufacturers are usually reluctant to provide the information with the necessary details for modelling.The aim of this report is to study the effect of slight alterations in simulating the intrinsic beam parameters and Linac configurations. The electron beams of the ELEKTA SL18 were simulated for different energies and field sizes using BEAMnrc. The output phase space files were used as input sources on a water phantom created using DOSXYZnrc. Different sources of systematic sources of errors in the simulation were investigated by slight alterations in beam and phantom parameters including the electron energy width of the beam, the source to surface distance and the voxel size, in addition to alterations in some Linac components such as, the walls of the scattering foils, the configuration of ionization chamber and the mirror, the jaws opening in addition to the materials of applicators. This was performed for a 10x10 field for a low energy (4MeV), moderate electron energies (8 MeV and 15 MeV) and high electron energy (18 MeV) at different source to surface distances (SSD). This work shows the necessity of the accuracy of simulating some of the beam parameters, the water phantom and the different Linac configurations and explains systematic errors that arise from slight alterations in these values. Percent depth dose curves are more influenced by accurate modelling of the different parts of the linear accelerator, especially the scattering foils, the monitor ionization chambers and the applicator materials. Beam parameters, source-to-surface distance, voxel sizes as well as some Linac components such as scattering foil walls, jaws opening and material of the applicators affect the off-axis dose distributions especially in the plateau and the shoulder regions.