INACTIVATION INDUCED BY DEUTERONS OF VARIOUS LET IN V79 CELLS

The results for inactivation of V79 cells irradiated by monoenergetic deuterons with LET of 18, 26 and 31 keV.mum-1 and their direct compari son with protons of comparable LET are presented. The experimental res ults show that at 31 keV.mum-1 cell inactivation is similar for proton s and deuterons while, at lower LET, deuterons appear to be less letha l than protons. The use of parameters other than L(infinity), such as L100 or Z2eff/beta2, does not completely reconcile the differences in biological effectiveness among the particles pointing out their inadeq uacy for describing the radiation quality of light ions. The experimen tal results have been compared with the Monte Carlo track structure si mulations, using the code MOCA 14, carried out for monoenergetic track segments of protons, deuterons and alpha particles of selected LET in the range 20-40 keV.mum-1. Existing track structure codes, and indeed essentially all other physical descriptions of radiations used to dat e, are unable to explain the observed differences in biological effect iveness between deuterons and protons.