Validation of monte carlo dose simulation for high-energy radiotherapy beams with symmetric and asymmetric fields using

Abstract

Accurate dose calculation is crucial in radiotherapy to effectively treat tumors while protecting healthy tissue. Monte Carlo (MC) simulation is widely recognized for its precision in modeling complex particle interactions and geometries. However, its clinical application requires thorough validation through experimental dosimetry, particularly when auditing high-energy photon beams with off-axis dose components, where beam modulation and tissue heterogeneities can significantly affect dose accuracy. This study aims to validate an MC simulation model by comparing simulated absorbed doses in water with dosimeter measurements under high-energy photon beams, covering both reference and non-reference conditions. Thermoluminescence dosimeter (TLD-100) were calibrated against an ionization chamber (IC) for 6 MV and 10 MV photon beams. Absorbed dose measurements were obtained using TLD- 100 across eight fields, including symmetric, asymmetric, wedged, and half-beam configurations. Each TLD were irradiated with a dose of 2 Gy. The MC model of the Elekta Versa HD linac was developed using GATE (Geant4), calibrated based on percentage depth dose (PDD) data. The validated model was subsequently used to simulate both reference and non-reference fields. The coefficient of variation (CV) for TLD and IC measurements was 1.12% (on-axis) and 1.27% (off-axis), confirming consistency across positions. Comparison between simulated and measured PDD curves yielded a gamma passing rate (3%/3 mm) of 100% for 6 MV and 97% for 10 MV, indicating strong agreement at all depths. The percentage relative deviation (PRD) for TLD and MC, when compared to IC measurements, were within ±5%. The mean ratios of DIC, DTLD, and DMC to DTPS for on-axis, wedge transmission, and output factors were 0.989, 1.003, and 0.998, respectively. This study demonstrates that MC simulation is a reliable and accurate method for dose verification in high-energy photon beams, showing strong agreement with TLD even under complex irradiation conditions. By providing critical validation evidence, the study supports the integration of MC methods into clinical workflows, enhancing treatment planning precision and advancing radiotherapy practices in accordance with international standards for quality and patient safety.