The irradiation of V79 mammalian cells by protons with energies below 2 MeV. Part I: Experimental arrangement and measurements of cell survival.

The relative biological effectiveness (RBE) has been determined for protons with mean energies of 1.9, 1.15 and 0.76 MeV, from measurements of the survival of V79 Chinese hamster cells. The cells are supported as a monolayer and are swept through a beam of scattered protons produced using a 4 MeV Van de Graaff accelerator. An estimation of the dose and unrestricted linear energy transfer (LET) variation within the sensitive volume of the cells is given for the three proton energies. The RBEs for cell survival (relative to 250 kVp X-rays) at the 10 per cent survival level are 1.6, 1.9 and 3.36 for protons with track-average LETs of 17, 24 and 32 keV microns-1 respectively, and the data suggest that protons are most effective at about 40-50 keV microns-1. It is shown that the proton RBEs can be reconciled with those of other light ions if plotted against z*2/beta 2 (where z* is the effective charge and beta is the relative velocity) rather than against LET.