Abstract
Linear non-threshold (LNT) model is a basic theory for radioprotection, but the adaptability of this hypothesis to biological responses at low doses or at low dose rates is not sufficiently investigated. In this study, some methods for quantitative risk assessment in dose response of biological reaction to low dose gamma radiation are proposed.
For defining statistically no risk level, we adapted some statistical models to quantitative data at low dose with statistically sufficient accuracy, using micronucleus formation of human osteosarcoma, and compared them with other statistical indexes corresponding to "threshold limit". The estimated values of statistically no risk levels remarkably increased with an increase of irradiation time. This indicates that the risk is reduced at low dose rates. Moreover, the values of statistically no risk levels and their confidence intervals depend on definitions of the value and on statistical models. These results suggest that we should statistically define the term "threshold" and include dose rate effects in the risk assessment model for estimating the low dose radiation risk and its uncertainty.
