Inactivation of V79 cells by low-energy protons, deuterons and helium-3 ions.

Previous work by ourselves and by others has demonstrated that protons with a linear energy transfer (LET) about 30 keVmum(-1)are more effective at killing cells than doubly charged particles of the same LET. In this work we show that by using deuterons, which have about twice the range of protons with the same LET, it is possible to extend measurements of the RBE of singly charged particles to higher LET (up to 50 keVmum(-1). We report the design and use of a new arrangement for irradiating V79 mammalian cells. Cell survival measurements have been made using protons in the energy range 1.0-3.7 MeV, deuterons in the energy range 0.9-3.4MeV and 3He2+ ions in the energy range 3.4-6.9 MeV. This corresponds to volume-averaged LET (within the cell nucleus) between 10 and 28 keVmum(-1) for protons, 18-50 keVmum(-1) for deuterons, and 59-106 keVmum(-1) for helium ions. Our results show no difference in the effectiveness of protons and deuterons matched for LET. However, for LET above about 30 keVmum(-1) singly charged particles are more effective at inactivating cells than doubly-charged particles of the same LET and that this difference can be understood in terms of the radial dose distribution around the primary ion track.