Dose divergence between monte carlo simulation and experimental measurements in the build-up region for a photon beam

Abstract

The aim of this work was to study the divergence between simulation and experimental measurements in the build-up region using two types of medical accelerators Elekta Synergy MLCi2 and Varian clinac 2100C and also for two types of ionization chambers. The Monte Carlo simulation was performed using the G4Linac-MT code. By demonstrating the variation of the particles in the build-up region, this work allows us to give an exact conclusion on the divergence between the Monte Carlo simulation and the experimental measurements.Using multi-threading code G4Linac-MT and the performance of the HPC-Marwan computing grid, we carried out simulations of large events with a saving in computing time. After optimizing the initial beam parameters, we looked for the ideal voxel size which corresponds to a better agreement between simulation and measurements to avoid simulation errors. The divergence between simulation and measurements in the build-up region is studied according to the type of ionization chamber, the irradiation fields, the source-to-surface distance (SSD) and the photon energy.The results obtained indicate that the dose divergence in the build-up region increases with the appearance of the contamination particles. The secondary particles detected in the build-up region are electrons and positrons for the 6 MV photon beam and other particles are added for the high energy beam 18 MV, including protons and neutrons. The dose accuracy of the comparison between the simulation and the measurements of the Varian 2100C and Elekta Synergy MLCi2 accelerators increases if the voxel size is small. A good agreement between the simulation and the experimental measurements in the build-up region is that which shows almost stable contamination of the particles up to the depth of electronic equilibrium.