Room: ePoster Forums
Purpose: To quantify the amount of secondary neutrons produced in a proton passive scattering nozzle and identify major nozzle components that produce most secondary neutrons by conducting Monte Carlo (MC) simulations.
Methods: The TOPAS (TOol for PArticle Simulation) MC code, an application of the Geant4 MC toolkit, was used to simulate a version of the IBA (Ion Beam Applications) universal proton therapy nozzle. The full nozzle geometry from the vacuum window to the compensator was simulated to deliver proton beams to the water box phantom (40 x 20 x 20 cmÂ³) distant 20 cm from the nozzle exit. Neutron fluences contributed from each nozzle component were then scored on the phantom surface closest to the nozzle exit by using TOPAS filtering scores. Simulations were run with 10â?¸ particles per simulation on the NIH HPC Biowulf cluster.
Results: Most secondary neutrons were produced from the aperture and compensator. Particularly, the aperture produced more secondary neutrons compared to the compensator. The total neutron fluence per million protons is 7182 from the aperture and 2270 from the compensator.
Conclusion: This work shows that the aperture and compensator are the major nozzle components inducing most secondary neutrons, which eventually determine out-of-field patient dose of interest in risk assessment of late effects. The same observation was also found in previous studies. Based on the result of the present study, we are planning to develop a streamlined, generic MC model focusing on simulating patient-specific aperture and compensator to estimate out-of-field organ/tissue doses of patients in multiple proton centers in the future.