Physical characterization of ³ He ion beams for radiotherapy and comparison with ⁴ He

There is increasing interest in using helium ions for radiotherapy, complementary to protons and carbon ions. A large number of patients were treated with 4 He ions in the US heavy ion therapy project and novel 4 He ion treatment programs are under preparation, for instance in Germany and Japan. 3 He ions have been proposed as an alternative to 4 He ions because the acceleration of 3 He is technically less difficult than 4 He. In particular, beam contaminations have been pointed out as a potential safety issue for 4 He ion beams. This motivated a series of experiments with 3 He ion beams at Gesellschaft für Schwerionenforschung (GSI), Darmstadt. Measured 3 He Bragg curves and fragmentation data in water are presented in this work. Those experimental data are compared with FLUKA Monte Carlo simulations. The physical characteristics of 3 He ion beams are compared to those of 4 He, for which a large set of data became available in recent years from the preparation work at the Heidelberger Ionenstrahl-Therapiezentrum (HIT). The dose distributions (spread out Bragg peaks, lateral profiles) that can be achieved with 3 He ions are found to be competitive to 4 He dose distributions. The effect of beam contaminations on 4 He depth dose distribution is also addressed. It is concluded that 3 He ions can be a viable alternative to 4 He, especially for future compact therapy accelerator designs and upgrades of existing ion therapy facilities.