Biokinetics of131I in the human organism

Time evolution of the cumulated activity in human body is one of the key 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 fitting a straight line in semi-logarithmic coordinates. Its novel Bayesian estimate was also proposed and its advantageous properties were verified. During extensive tests, it was found that the effective half-life has limited use as the underlying deterministic relationship time-activity can hardly be taken as (mono)exponential. It stimulated the search for a better and still simple model. A quadratic dependence of ln (activity) on ln (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 made in verifying and exploiting this non-standard model. Its potential exploitation in dosimetric tasks is outlined. The core of the paper describes a positive verification of our results on an extensive set of real data.