Abstract
LNT model is a basic theory for the regulation of radioprotection, it does not consider irradiation time or dose-rate. We have established Modified Exponential (MOE) model describing dose-rate effect of ionizing radiation. The model is not based on any physiological mechanism, but is derived from curve-fitting to data by an optimal function. Another model is designed based on a simple mechanistic hypothesis. The assumption is that the effects during one generation are restricted only in the generation, in other words that the effects in the previous generation are cancelled in the next generation. Cells then receive full dose from instantaneous dose, whereas the effects reduce with longer exposure. The model gives an iso-effect curve on the dose-dose-rate domain, converging to total dose as an asymptotic line in the high dose-rate region, and also to an asymptotic line with dose rate of total dose/generation time in the low dose-rate region. The data of the micronucleus formation with the rate 22% are compared with the model. The match was good in data up to 1200h, but the data shifted to higher dose-rate when exposure further extended. For the data of the inhibition of [3 H]thymidine uptake, the data for 50% inhibition showed fairly good agreement up to 170h, but the data shifted to low dose-rate in longer exposure.
