Dosimetric Comparison of Passive Scattering and Active Scanning Proton Therapy Methods using GATE Simulations

In this study, two different proton beam delivery designs, i.e. passive scattering (PSPT) and active scanning (PBS), were first evaluated with respect to experimental measurements and then quantitatively compared in terms of dosimetric indices. The GATE Monte Carlo (MC) particle transport code was used to simulate the two proton beam designs. We calculated dosimetric parameters including Full Width at Half Maximum (FWHM or W
50
), peak position, range, peak-to-entrance dose ratio, and dose volume histogram (DVH) for the two proton beam models under similar conditions. A water phantom was used to simulate system energy parameters using a set of depth-dose data in an energy range of 120-235 MeV. Furthermore, the clinical test cases introduced by AAPM TG-119 were simulated in both beam delivery modes to compare relevant clinical parameters obtained from DVHs. The parametric comparison in the water phantom between the two techniques revealed that the value of peak-to-entrance dose ratio in PSPT mode is considerably higher than that obtained from PBS by a factor of 8%. In addition, the W
50
of the lateral beam profile in PSPT was increased by a factor of 7% compared to the corresponding value obtained from PBS model. TG-119 phantom simulation showed that the maximum dose and mean dose to organs at risk (OARs) in PSPT mode are 20% and 16% greater than PBS, respectively. The results demonstrated that the PBS system offers superior performance in adapting to the target volume, better control on dose distribution, and lower extra-target dose compared to passive scattering design.