  In this study, two proton beam delivery designs, passive scattering proton
therapy (PSPT) and pencil beam scanning (PBS), were quantitatively compared in
terms of dosimetric indices. The GATE Monte Carlo code was used to simulate the
proton beam system; and the developed simulation engines were benchmarked with
respect to the experimental measurements. A water phantom was used to simulate
system energy parameters using a set of depth-dose data in the energy range of
120-235 MeV. To compare the performance of PSPT against PBS, multiple
dosimetric parameters including FWHM, peak position, range, peak-to-entrance
dose ratio, and dose volume histogram have been analyzed under the same
conditions. Furthermore, the clinical test cases introduced by AAPM TG-119 were
simulated in both beam delivery modes to compare the relevant clinical values
obtained from DVH analysis. The parametric comparison in the water phantom
between the two techniques revealed that the value of peak-to-entrance dose
ratio in PSPT is considerably higher than that from PBS by a factor of 8%. In
addition, the FWHM 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 simulations showed that the difference of PTV mean dose between
PBS and PSPT techniques are up to 2.9% while the difference of max dose to
organ at risks (OARs) exceeds 33%. The results demonstrated that the PBS proton
therapy systems was superior in adapting to the target volume, better dose
painting, and lower out-of-field dose compared to PSPT design.
