Radiobiological studies for helium ion therapy of uveal melanoma

This report summarizes part of the radiobiology that has been done at Berkeley's 184-Inch Cyclotron with helium-ion beams, which are currently being used to successfully treat uveal melanoma. There were two main objectives to this study. The first was to confirm the adequacy of ridged filter design to achieve uniform cell killing across narrowly collimated and narrowly extended Bragg peaks of only a few centimeters in depth of range, which primarily involved measuring the RBE in vitro by two independent types of experiments. The second objective was to compare the physical and biological usefulness of a 308-MeV/u Bevalac-accelerated carbon beam for its potential application to the treatment of small localized volumes near critical structures. Two conclusions have been drawn from this work: 1. The RBE measured in vitro in the 230 MeV/u helium-ion extended Bragg peak is 1.3-1.6. 2. Isoeffective biological response can be achieved with variable absorber filters that produce narrowly collimated Bragg peaks extended only a few cm for treatment of uveal melanoma