Evaluation of cubic voxel effects on dose calculation for Iridium-192 high dose rate using TOPAS particle simulation

Abstract

Background: This study investigates the impact of voxel size on dose calculations for the FlexiSource iridium-192 ( 192 Ir) high-dose-rate brachytherapy source using the TOol for PArticle Simulation (TOPAS) Monte Carlo code. It aims to establish a new dataset for future research by determining TG-43 parameters. Materials and methods : TG-43 parameters (radial function and anisotropy function) were calculated using 0.5 mm³ and 1 mm³ voxel sizes. Mean dose calculations were performed at various distances from the source. The 192 Ir spectrum from the National Nuclear Data Center (NNDC) was utilized. Results: The measured air-kerma strength per unit source activity differed by 2.34% from consensus data. Radial function analysis showed consistent results, with 0.5 mm³ voxels deviating up to 1.78% near the source and 7% at greater distances. The 1 mm³ voxels showed similarities at greater distances (up to 1.52% deviation) but significant differences near the source (up to 20% deviation). Anisotropy function analysis revealed variations of 3–4% for angles < 7° and > 175° with 1 mm³ voxels, and 10–20% for angles < 12° and > 177° with 0.5 mm³ voxels compared to Carleton Laboratory for Radiotherapy Physics (CLRP) reference values. Conclusions: These findings validate the TOPAS Monte Carlo code's accuracy for dose calculation and emphasize the importance of voxel size selection. The generated dataset shows promise for future research efforts in brachytherapy dose calculations.