Micronuclei Induced by Fast Neutrons Versus ⁶⁰Co γ-rays in Human Peripheral Blood Lymphocytes

Abstract

Here we compared the effectiveness of neutrons (〈E〉 = 5·5 MeV) versus ⁶⁰Co γ-rays in producing micronuclei (MN) in human lymphocytes. To obtain dose-response data, blood samples of six donors were irradiated with doses ranging from 0·1 to 5 Gy for γ-rays and 0·1–3 Gy for neutrons. A linear dependence of MN yield with dose was found for fast neutrons while for γ-rays a nonlinear dependence existed. For both radiation qualities no significant interindividual differences were found. Derived relative biological effectiveness values decreased with increasing dose. The MN frequency distributions were overdispersed with respect to the Poisson distribution, with neutrons showing higher dispersion values than with γ-rays. To compare the repair kinetics of both radiation qualities split-dose experiments were performed. A dose of 4 Gy γ-rays (3 Gy neutrons) was delivered either as a single exposure or in two equal fractions separated by time intervals ranging from 30 min to 10h (30 min to 7h for neutrons). The data showed for γ-rays a significant decline (30% ± 10%) in MN yield with interfraction time due to repair of DNA damage. This repair is a continuous process starting almost immediately after the first of the two doses and lasting 3–5h. For fast neutrons no decline was observed indicating irreparable damage.