Chromosome aberrations induced by protons up to 31 MeV in cultured human cells

Chromosome aberrations were induced in cultured human cells by proton beams of 31, 12, and 8 MeV. The frequencies of isochromatid breaks and dicentrics have been analysed as a function of proton energy and dose. Both effects are largely dependent on proton energy; isochromatid breaks increased linearly with the dose, whereas dicentrics show a definite parabolic behaviour. The experimental data were fitted to the analytic form Y = KDn and Y = alpha D + beta D2 and the best fitted values of the parameters are reported and discussed. The values of RBE for the isochromatid breaks are in the ratio 1.7:1.3:1 for 8, 12, and 31 MeV respectively. In the case of the dicentrics the RBE values are dose-dependent function of the type CD-n. The three distributions of dicentrics among the cells do not fit a Poisson distribution.