Dose-rate effect on radiation-induced DNA double-strand breaks in the human fibroblast HF19 cell line

Abstract

Abstract. We measured DNA double-strand breaks (dsbs) immediately after exposure of a non-transformed human fibroblast cell line (HF19) to gamma-rays (0-40 Gy) at four doserates (10, 1, 0. 1, and 0.01 Gy.min- 1) at 37degreeC using clamped homogeneous electric field (CHEF) gel electrophoresis. The shape of the dose-response curves, which could be approximated by a straight line over the range 0-20 Gy for irradiation at 4degreeC, became curvilinear when irradiation was carried out at 37degreeC at 10, 1, 0.1, and 0.01 Gy.min- 1 and reached a plateau at 10 Gy after irradiation at 0. 01 Gy.min- 1. We present a mathematical analysis that predicts the results of irradiation at 37degreeC from dsb induction and repair data obtained at 4degreeC, followed by incubation for repair at 37degreeC. The model assumes that the rate of dsb rejoining changes continuously with repair time and that it is independent of dose and dose-rate in the range 10-40 Gy. The model also assumes a linear induction of dsb with dose at 4degreeC and dsb induction is independent of dose-rate and of temperature during irradiation. Independent measurements of dsb induction at 4degreeC and of repair rate accurately predict the dsb levels after irradiation at 37degreeC, during which both phenomena occur simultaneously.