Log Normal Distribution of Cellular Uptake of Radioactivity: Implications for Biologic Responses to

It is widely recognized that radiopharmaceuticals are generally distributed nonuniformly in tissues. Such nonuniformities are ob-served over the entire range of spatial levels, ranging from organ to subcellular levels. The implications of nonuniform distributions of radioactivity for dosimetry, and ultimately for the biologic re-sponse of tissues containing radioactivity, have been investi-gated extensively. However, there is a paucity of experimental data on the distribution of cellular activity within a population of cells. In the present study, the distribution of activity per cell is ex-perimentally determined and its implications for predicting bio-logic response are examined. Methods: Chinese hamster V79 cells were exposed to different concentrations of 210Po-citrate. The radiolabeled cells were washed, seeded into culture dishes or glass slides, covered with photographic emulsion, and stored in an opaque container. Subsequently, the emulsion was devel-oped, thereby resulting in observable a-particle tracks that were scored.Results: The distribution of activity per cell was found to be well described by a log normal distribution function. Theoretic modeling of cell survival as a function of mean activity per cell showed that survival curves differed substantially when the activ-ity per cell was log normally distributed versus when it was as-sumed conventionally that every cell in the population contained the mean activity. Conclusion: The present study provides ex-perimental evidence of log normal cellular uptake of radioactivity. Theoretic calculations show that a log normal distribution of cel-lular activity can have a substantial impact on modeling the bio-logic response of cell populations. Key Words: log normal distribution; 210Po; autoradiography; a-particle; cellular dosimetr