Validation of Monte Carlo Simulations with GAMOS for the Elekta Synergy Agility LINAC: Comparative Study of UBS, DBS, and EWBS Variance Reduction Techniques

The Monte Carlo code GAMOS 6.2.0, based on version 10.06.p02 of GEANT4, was employed to model the Elekta Synergy Agility linear accelerator (Linac). The Linac’s irradiation head was simulated by modeling the target, primary collimator, flattening filter, ionization chamber, and the X and Y jaws. Phase spaces were then simulated after the X and Y jaws for each variance reduction technique: UBS (Uniform Bremsstrahlung Splitting), DBS (Directional Bremsstrahlung Splitting), and EWBS (Equal Weight Bremsstrahlung Splitting), with field sizes of 5 × 5 cm² and 10 × 10 cm². The dose distribution was subsequently calculated for each variance reduction technique in a homogeneous water phantom at depths of 5 cm, 10 cm, 15 cm, and 20 cm. The results obtained were compared with experimental data using the gamma index, with an acceptance criterion of 3% for dose difference (DD) and 3 mm for distance-to-agreement (DTA). For a 5 × 5 cm² field size, a 94% agreement was obtained between the simulated and experimental data for depth-dose curves using the three techniques: EWBS, DBS, and UBS. Regarding dose profiles, the EWBS, DBS, and UBS techniques showed excellent agreement of 100% with the experimental data for a 5 × 5 cm² field at a depth of 5 cm. At 10 cm depth, the EWBS technique achieved 100% agreement, followed by DBS at 98%. At 15 cm depth, EWBS and DBS also showed 100% agreement, while UBS achieved 97%. Finally, at 20 cm depth, EWBS presented 100% agreement, followed by DBS and UBS at 99%. For a 10 × 10 cm² field size, a 96% agreement was achieved between the simulated and experimental data for depth-dose curves with the three techniques: EWBS, DBS, and UBS. Regarding dose profiles, the EWBS technique showed 99% agreement, followed by DBS at 98% at a depth of 5 cm. At a depth of 10 cm, EWBS showed 99% agreement, followed by UBS at 98%. At 15 cm depth, EWBS reached 100% agreement, followed by DBS at 99%. Finally, at 20 cm depth, EWBS maintained 100% agreement, followed by DBS at 97%. The results of this study are significant for medical physics applications, as they can guide radiotherapy practitioners in selecting the most appropriate technique for their simulations. Thus, this paper contributes to the advancement of simulation method development and validation, which can ultimately lead to safer and more effective treatments for cancer patients.