Improving dose accuracy in radiation therapy: Validating monte carlo simulations with GATE and PRIMO

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.

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.

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.

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.