SU-E-T-22: Is the Residual Range a Universal Quantity to Specify the Quality of Modulated Proton Beams?

Medical Physics
Dal A GranvilleG O Sawakuchi

Abstract

To investigate the validity of using the residual range as a universal quantity to specify the quality of modulated proton beams. We used TOPAS (Tool for Particle Simulation), an application of the Geant4 toolkit, to simulate absorbed dose and stopping-power distributions from a commercial passive scattering nozzle. We used the standard physics lists from Geant4 in the simulations. All particles were included, as well as physics models for nuclear interactions. No variance reduction techniques were used. Dose and averaged stopping-power as functions of depth were scored in a water box with 320 scoring volumes of 15 × 15 × 0.1 cm(3) . Stopping-power spectra were scored in a15 × 15 × 0.1 cm(3) volume located in the middle of SOBPs. All particles were considered in the dose scoring. Only protons (primary and secondary) were considered in the scoring of stopping-power. For the same residual range, differences in averaged stopping-power values of up to 13% were observed for a 200 MeV beam with modulations of 4 cm and 8 cm, respectively. Simulations of four modulated proton energies with the same SOBP of 8 cm showed differences of up to 13% in the averaged stopping-power values even in the SOBP region. We also simulated stopping powe...Continue Reading

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