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

There is increasing interest in using helium ions for radiotherapy, complementary to protons and carbon ions. A large number of patients were treated with ⁴He ions in the US heavy ion therapy project and novel ⁴He ion treatment programs are under preparation, for instance in Germany and Japan. ³He ions have been proposed as an alternative to ⁴He ions because the acceleration of ³He is technically less difficult than ⁴He. In particular, beam contaminations have been pointed out as a potential safety issue for ⁴He ion beams. This motivated a series of experiments with ³He ion beams at Gesellschaft für Schwerionenforschung (GSI), Darmstadt. Measured ³He 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 ³He ion beams are compared to those of ⁴He, 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 ³He ions are found to be competitive to ⁴He dose distributions. The effect of beam contaminations on ⁴He depth dose distribution is also addressed. It is concluded that ³He ions can be a viable alternative to ⁴He, especially for future compact therapy accelerator designs and upgrades of existing ion therapy facilities. (paper)