Room: Exhibit Hall | Forum 4
Purpose: To develop a Monte Carlo (MC) simulation model for the passive double scattering compact Mevion S250 proton therapy system based on limited information of the mechanical components.
Methods: We have designed a virtual passive double scattering proton machine for Monte Carlo simulations. The model includes all major beam modifying/shaping components that interact with the proton beam along the beam path. The field shaping system (FSS) was constructed based on the machine configuration data and the individual components (range modulation wheels (RMWs), absorbers, first and second scatterers) are tuned numerically, to generate proton beams which agree with the measurement data as closely as possible. Specifically, the pristine Bragg curves were used to derive the thickness of the thinnest step of the wheel. For each beam option (24 total in the Mevion S250 system), a full modulation was used to guide the design of the RMWs. The validation of the RMW design was carried out by comparing the measured spread out Bragg peaks (SOBPs) of other modulations besides the full modulation with the MC calculations. The model was validated by comparing percent depth dose curves, SOBPs and lateral profiles against measured beam data.
Results: The agreement of beam range (90% depth) between the MC calculation and measurement was within 1 mm for all beam options. The distal-falloff length was in good agreement as well. Agreement to within 2.5 mm of measured SOBP widths was obtained for all MC calculations.
Conclusion: We demonstrated that with limited geometrical information it is possible to construct a virtual machine source mode for a passive double scattering compact proton therapy system. The agreement between the measurements and the MC model provides validation for use of the model in further study on the dosimetric effect in patient treatments