BIOKINETICS OF I-131 IN THE HUMAN ORGANISM

Time evolution of the cumulated activity in human body is one of the k ey characteristics determining medical impacts of ionizing radiation. In nuclear medicine, so called effective half-life is mostly used for describing the evolution. This quantity is usually estimated by fittin g a straight line in semi-logarithmic coordinates. Its novel Bayesian estimate was also proposed and its advantageous properties were verifi ed. During extensive tests, it was found that the effective half-life has limited use as the underlying deterministic relationship time-acti vity can hardly be taken as (mono)exponential. It stimulated the searc h for a better and still simple model. A quadratic dependence of in (a ctivity) on in (time) was found as an adequate candidate. Preliminary experiments on a restricted set of real data were promising enough to justify its further elaboration. The paper reports on the progress mad e in verifying and exploiting this non-standard model. Its potential e xploitation in dosimetric tasks is outlined. The core of the paper des cribes a positive verification of our results on an extensive set of r eal data.