Inactivation of C3H10T1/2 cells by low energy protons and deuterons

Purpose: To determine the RBE-LET relationship for C3H10T1/2 cell inactivation by protons in the LET range 11-33 keV/ mu m and to compare inactivation frequencies induced in C3H10T1/2 cells by protons and deuterons at two matching LET values in the range 11-20 keV/ mu m. Materials and methods: C3H10T1/2 cells were irradiated with protons and deuterons at the radiobiological facility set up at the 7 MV Van de Graaff accelerator at the LNL, Legnaro, Padova. Gamma rays from 60Co were used as reference radiation. Results: Proton RBE values (alpha / alpha c) for inactivation of C3H10T1/2 cells are constant around a value of 2 between 11 and 20 keV/ mu m and then rise sharply to reach a value of 4.2 1.0 at 33 keV/ mu m. Deuteron RBE values are 1.7 0.4 and 2.2 0.6 at LET values of 13 and 18 keV/ mu m respectively. Conclusions: Proton RBE values with C3H10T1/2 cells are significantly larger than unity at LET values as low as 11 keV/ mu m. No difference in effectiveness for inactivation of C3H10T1/2 has been found between protons and deuterons at two LET values in the range 10-20 keV/ mu m.