A comprehensive GATE Monte Carlo model for a double scattering proton treatment nozzle

Proton beam therapy (PBT) is a modern radiotherapy technique characterized by superior target coverage compared to conventional modalities. In this work, a comprehensive GATE Monte Carlo model was developed and then validated for a double scattering proton treatment nozzle. To this aim, a double scattering treatment nozzle was modeled in the GATE toolkit. Proton beam flatness and its symmetry, secondary neutron effective dose, and dosimetric performance were characterized. A proton beam flatness of 98.6% was observed 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. Compared to the single scattering delivery, the second scattering model results in a 1.3 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 the GATE and MCNPX codes. The GATE model agreed with the MCNPX results. The results show that the constructed GATE model results in a fast and accurate simulation of passive scattering PBT.