PARENT SESSION

Risks and Modeling at Low Doses

(PP047) Multicellular dosimetry as an approach to predict the biological response to nonuniform distributions of Po-210.

Neti, Prasad^*,1, Howell, Roger¹, ¹ Dept. of Radiology, Division of Radiation Research, Newark, New Jersey, US

ABSTRACT- To varying degrees, radioactivity is distributed nonuniformly in tissue. At a macroscopic level, radioactivity may appear to be uniformly distributed throughout the tissue. Upon closer inspection, not all cells in the tissue may be labeled. The present work examines the impact of nonuniformities at the multicellular level on the lethal effects of the alpha-emitter Po-210. A three-dimensional tissue culture model was used to investigate the biological effects of nonuniform distributions of Po-210. Chinese hamster V79 cells were labeled with Po-210-citrate, mixed with unlabeled cells in various proportions (1, 10, or 100%), and multicellular clusters were formed by gentle centrifugation (4x10⁶ cells). Thus, the labeled cells were randomly located in the cluster to achieve a uniform distribution of radioactivity at the macroscopic level, yet nonuniform at the multicellular level. The clusters were assembled as described and then maintained at 10.5°C for 72 h to allow alpha-decays to accumulate. The clusters were then dismantled and the cells were plated in triplicate for colony formation. Two-component exponential dose-response curves were observed for all three labeling conditions (1, 10, 100%). Furthermore, the slopes of the survival curves were significantly different for each labeling condition. In view of the inability to predict response based on the mean absorbed dose to the cluster, a multicellular dosimetry approach is advanced to predict the observed responses. This work was supported in part by USPHS R01CA83838.

Key words: alpha particles, radioactivity, dosimetry, survival