While protracting exposures of low-LET radiations usually leads to a reduction in their effectiveness for a given dose, for high-LET radiation there is now substantial evidence for what has been called an inverse dose-rate effect, where under certain circumstances there is an increase in carcinogenesis or other biological effects, with decreasing dose rate. This study investigates the influence of dose rate on the induction of chromosome aberrations and gene mutations after irradiation of plateau phase V79-4 cells with high-LET alpha particles. The induction of chromosomal aberrations exhibited a linear relationship with dose and showed evidence of a small but significant conventional dose-rate dependence, with low-dose-rate exposures (0.28 Gy h−1) being less effective by about 20% (ratio 0.82 ± 0.04) compared to acute exposures. However no significant dose-rate effect was observed for cell survival or the induction of mutations in the HPRT gene for low-dose-rate exposure (8.0 × 10−5 and 1.5 × 10−2 Gy h−1 for exposure of 0.36 and 0.69 Gy, respectively) when compared to acute exposures.
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Vol. 182 • No. 3