RBE-LET relationships for V79 cells irradiated with low energy protons

Mutation curves of V79 Chinese hamster cells irradiated with low energy proton beams of LET ranging from 10 to 34 keV.μm-1 have been studied in the dose range 0.5-2.0 Gy and compared with that obtained using 200 kV X rays. A substantial difference in the number of induced mutants, at the same dose, has been found when comparing protons and X rays, protons being more effective. The relative biological effectivenesses (RBE) for mutation, evaluated as the α/αx ratios, were found to be significantly higher than those expected using heavier particles, in agreement with the results recently obtained for survival. This finding is discussed in terms of general validity of the 'classical' RBE-LET relationship when different types of radiations are compared. (author)