Background & Aim: Optimizing radiation dose in radiotherapy treatments is of great importance. Monte Carlo simulation of medical linear accelerators is a key tool for enhancing precision and reliability in treatment planning, reducing radiation risks, improving treatment quality and effectiveness, and saving time and resources.
Methods: In this study, the treatment head components of a Varian Clinac 2100 linear accelerator were modeled using the GATE/ GEANT 4 code (version 8.2) and the PRIMO simulation software (version 0.3.64.1841). The developed model was validated for a 6 MeV photon beam using the phase-space technique in both PRIMO and GATE codes, as well as the conventional dose calculation method in GATE. The calculated results were compared with measurements conducted in a water phantom with dimensions of 50 × 50 × 30 cm³ at a source-to-surface distance (SSD) of 100 cm. Percentage depth dose (PDD) and transverse profiles were calculated at a depth of 10 cm and at the depth of maximum dose for field sizes of 5 × 5 cm², 15 × 15 cm², and 30 × 30 cm².
Results: Dosimetry was performed using voxel sizes of 2 × 2 × 2 cm³ for percentage depth dose and 5 × 5 × 2 mm³ for transverse profiles. The optimal parameters, including an average electron beam energy of 6.2 MeV, a standard deviation of 0.17 MeV, and an electron source size of 2 mm, were determined, showing good agreement between simulation and measurement results.
Conclusion: The results indicated that the mean point-to-point deviation was less than 2.5%, and 95.56% of the evaluated points met the gamma index criterion of 3/3% mm. This study confirms the capability of the PRIMO and GATE codes in radiotherapy applications.
