A Fast and Accurate GATE Model for Small Field Scattering Proton Beam Therapy

Abstract

Proton beam therapy (PBT) is a modern external beam radiation therapy characterized by superior dose distribution. Small field PBT refers to the treatment of tumor sizes less than 7 cm in diameter. In this study, a fast and accurate GATE model was developed and then validated for a small field scattering PBT delivery. To this aim, a fixed single scattering nozzle was modeled in the GATE platform. To accelerate the GATE simulations, a variance reduction technique (VRT) was also incorporated by ignoring the tracking of the secondary particles having a range below a predefined cutoff. In addition, the influence of collimator material on the model performance was evaluated. Beam uniformity, secondary neutron dose, and dosimetric performance were assessed through a set of phantom studies. The VRT leads to 1.25 times faster GATE simulations. A beam uniformity of 93% was observed at the downstream side of the collimator for a 7 × 7 cm2 field size. The beam uniformity worsens at the edge of the treatment field. Nickel was found to be the optimal collimator material by imposing the lowest secondary neutron dose into a water phantom. An approximately flat modulation width of 3.5 cm is formed with a distal edge at 7.8 cm in water using both GATE and MCNPX codes. The results reveal that the GATE model is in good agreement with the MCNPX results with a maximum difference of ±7% in absorbed dose estimation. The findings demonstrate that the developed GATE model results in an accurate and fast simulation of small field scattering PBT.