[Extrapolation of dose-effect relationships for cytogenetic aberrations from high to low doses]

It is known, that extrapolation of dose response curve for cytogenic lesions, based on the linear non-threshold concept is not correct due to anomalies in the low dose region, among them the dose intervals of the so-called "low dose effects" (LDE) and "plato"-effect. As a rule they are attributed to assumed heterogeneity of cell populations or to existence of several repair systems. Analysing the data on modification the cytogenetic lesions we concluded, that in the whole low-dose range functions one on the same repair system, but it "switches on" only at sufficient reorganization of chromatin (accompanied by expression of before "silent" genes), caused by radiation-induced increase of the membranes permeability. In the dose interval of LDE this occurs only in vary narrow diapason of dose rate (approximately(1-30) cGy/min for many cell kinds); in the "plato" dose interval--in its beginning. By the assessment of cancerogenic risk the linear non threshold concept can be used only for dose dependence, obtained when repair is absent or inhibited.