SU-E-T-535: On the Out-Of-Field-Doses Caused by Secondary Particles From Light Ion Beams in Charged Particle Therapy

Abstract

Purpose: Charged ion therapy in the United States consists mainly of proton therapy, which may deposit a larger than necessary lateral dose to healthy tissues. Application of heavier particles may Result in an improvement, i.e., lowering the dose bath to the patient. The purpose of this study is to evaluate the secondary halo dose of therapeutic light ion beams. Methods: Monte Carlo simulations have been performed to evaluate lateral dose distributions (halo dose) caused by scattered primary particles as well as by secondary particles, in therapeutic ion beams. Primary particles included Protons, Helium ions, Lithium ions as well as 12C-ions. Energy deposition profiles in a water phantom from various particle species were evaluated and compared. The secondaries included heavy ions (heavier than alphas), alphas, protons, as well as neutrons and photons. The study provides estimates of out of field doses from secondary particles for a variety of beam parameters such as range in water, field size, modulation width, and the source particle type. Results: Preliminary data indicates, that with increasing Z of the source particles, lateral dose profiles, including scattered primary and secondary particles from nuclear reactions, decrease significantly. Conclusion: Further studies are indicated to evaluate any possible improvement in lateral dose deposition versus increased doses to tissues distal to the Bragg peaks, caused by source particle and target fragmentation.