Is micronuclei yield variability a problem for overexposure dose assessment to ionizing radiation?

Scoring of micronuclei (Mni) in cytokinesis-blocked human blood peripheral lymphocytes after an accidental radiation overexposure appears an easier and faster alternative for biological dosimetry than dicentrics analysis. However, an increase of Mni rate could be difficult to interpret particularly at low doses, because of the known variability of individual dose response and the unknown background frequency. Moreover, in case of nuclear emergency, there are the added problems of large samples numbers for processing and so screening time. In this paper, we wish to propose some solutions using both methodological and statistical approaches. Firstly, we have tried to check the micronuclei assay in order to obtain a sufficient number of micronuclei in binucleated cells in the shortest time possible, even at higher exposition dose. Two techniques were compared using frequencies of binucleated cells and micronuclei in normal lymphocytes and after exposure to gamma-irradiation (60 Co) for doses up to 6 Gy. Secondly, we have supposed that, if the individual radiosensitivity was a critical problem for dose estimation, conversely, it would be not possible to build a reference curve combining many individuals. Thus, we have assessed the Mni response from 47 carefully selected healthy male blood donors for gamma-irradiation between 0 and 4 Gy. We show in this study that a realistic dose-effect relationship could be always fitted. In addition, the related coefficients could be compared with other published dose-effect relationships for gamma rays. However, the background incidence calculated from these 47 healthy individuals were found to be larger as expected so that this approach increases the detection limit for which an overexposure suspicion could be significantly detected to 0.32 Gy.