INACTIVATION OF C3H10T1 2 CELLS BY LOW-ENERGY PROTONS AND DEUTERONS/

Purpose: To determine the RBE-LET relationship for C3H10T1/2 cell inac tivation by protons in the LET range 11-33 keV/mu m and to compare ina ctivation frequencies induced in C3H10T1/2 cells by protons and deuter ons at two matching LET values in the range 11-20 keV/mu m. Materials and methods: C3H10T1/2 cells were irradiated with protons and deuteron s at the radiobiological facility set up at the 7MV Van de Graaff acce lerator at the LNL, Legnaro, Padova. Gamma rays from Co-60 were used a s reference radiation. Results: Proton RBE values (alpha/alpha(gamma)) 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 18keV/mu m respectively. Conclusions: Proton RBE values with C3H10T1/2 cells are significantly larger than unity at LET Values as low as 11keV/mu m. No difference in effectivene ss for inactivation of C3H10T1/2 has been found between protons and de uterons at two LET values in the range 10-20keV/mu m.