Development and validation of an optimal GATE model for double scattering proton beam delivery

Abstract

Proton therapy (PT) is an emerging external beam radiation therapy characterized by superior dose distribution compared to conventional modalities. In the present study, an optimal GATE model was developed and then validated for a double scattering proton nozzle based on the previously constructed model. To this aim, a double scattering treatment nozzle was modeled in the GATE platform. To accelerate the GATE simulations, a virtual range modulation wheel (vRMW) and a variance reduction technique (VRT) were implemented. Proton beam flatness, symmetry, and delivery efficiency, secondary neutron dose, and dosimetric performance were characterized through a set of GATE simulations. The findings show that range cutoff value of 0.075 mm provides the best compromise between the simulation accuracy and speed for the simulated geometry. A proton beam flatness of 98.6% was observed at the downstream of the aperture for a 7 × 7 cm2 field size. The beam flatness deteriorates at the edge of the treatment field for the single scattering model while it remains approximately constant for the double scattering one. In comparison to the single scattering delivery, the second scattering model results in a 1.28 times increase in neutron dose for the nickel, as the optimal collimator/aperture material. Furthermore, a flat beam modulation width of 3.50 cm is formed with a distal edge at 7.86 cm in water using both GATE and MCNPX codes. The GATE model agreed with the MCNPX results with a maximum difference of ±6.3% in absorbed dose estimation. The findings demonstrate that the constructed GATE model of double scattering proton nozzle results in a fast and accurate simulation of passive scattering PT.