Usefulness of the simultaneous bioassay analysis method used for an intake estimation of a radionuclide.

An intake of a radionuclide is estimated based on bioassay measurement data obtained by an in vivo or an in vitro method. Often the intake estimates from one bioassay analysis are considerably different from other results. For better estimates, a simultaneous or combined analysis of measurement data from different bioassay methods is attempted. In this study, the usefulness of a simultaneous bioassay analysis was investigated by using the IDEAS/IAEA intercomparison exercise data and the Individual Monitoring of an Internal Exposure computer code. Tests were made for whole-body counting and urine assay against an acute inhalation of types M and S 60Co particles with various activity median aerodynamic diameter (AMAD). The data set excluding rogue data as well as all the available data were used in this study. The best estimated intake was evaluated based on the best-fit time of an intake determined by minimizing the mean relative deviation Dr. In the case of the whole-body and urine bioassay by using the data excluding some rogue data, the smallest Dr appears at 0.1 and 10 microm of AMAD, respectively, which are different from those estimated by using all the available data. In the case of the simultaneous analysis, it appears at 20 microm of AMAD, which is the same as that estimated by using all the available data. Supposing that monitoring data of a good quality is available, it is expected that the application of a simultaneous analysis to different bioassay methods can provide not only better estimates of an intake but also insights into the validity of the models and parameters used in an interpretation.