Evaluation of dosimetry quantities in passive scattering and spot scanning methods in proton therapy based on GATE simulation

Thespot-scan based methods are expected to perform better than other methods for proton therapy in delivering the dose to the intended target. In this study, the GATE computer code is used to evaluate important dosimetric quantities in proton therapy, such as Full width at half maximum, peak position, range and peak-to-entrance dose ratio (percentage depth dose) in the proton therapy process under the same conditions based on spot scanning and passive scattering. Water phantom was selected and system energy parameters were measured using a set of depth-dose curve in the energy range of 120 to 235 MeV. Bragg peaks were generated with an accuracy of 0.7 mm in range. Spread out Bragg-peak were produced with 7 cm modulation and 10 mm range accuracy and peak-to-entrance dose ratio difference at an input dose of 8%. To evaluate the versatility of the beam, the Full width at half-maximum was evaluated with a maximum difference of 7% between the two methods. As a result, based on the simulations performed for different beam delivery systems, the ability of the spot scanning method in adapting to the target volume, better control over dose distribution and less extra-tumor dose was demonstrated.