Abstract
Although linear non-threshold (LNT) is a basic theory for radioprotection, adaptability of LNT to biological responses at low dose/low dose-rate is not sufficiently investigated. In this study, we acquired quantitative data at low dose/low dose rate with statistically sufficient accuracy, using micronucleus formation of human osteosarcoma. These data were plotted on the coordinate of linearly scaled response and dose. The results followed to the straight line passing through the origin of the coordinate axes between 0.1-5 Gy when cells were irradiated for 1-10 min. The increase in binuclear cells bearing micronucleus was statistically significant at the dose above 0.1 Gy. In contrast, dose response curves never followed LNT and statistical significance was obtained at the doses above 6 Gy when cells were irradiated for 7 to 124 days. These results suggest that dose response curve of biological reaction is remarkably affected by exposure time, and that dose rate effect changes as a function of dose-rate and irradiation time. [J Radiat Res 44:392 (2003)]
