RELATIONSHIPS BETWEEN CELL-SURVIVAL AND SPECIFIC ENERGY-SPECTRA FOR THERAPEUTIC ALPHA-PARTICLE EMITTERS

Cell survival studies are a means of quantifying the biological effect s of radiation. However, for alpha-particle sources, the dose-response relationship is complicated by the dominance of microdosimetric effec ts. In this work, we relate observed cell survival to the microdosimet ric energy deposition spectra. The chord length distributions through spherical cell nuclei for sources distributed inside of, on the surfac e of and outside of the critical target are used as approximate analyt ical representations of the single-event specific energy spectra. Math ematical relationships are derived which relate cell survival to the L aplace transform of the single-event specific energy spectrum. The res ult is an analytical relationship between D-0 (the observed slope of t he cell survival curve) and z(0) (the specific energy required to redu ce the survival probability of a single cell to 1/e). These studies in dicate that for small energy deposition events, z(0) is approximately equal to D-0. However, as the maximum energy deposited by a single eve nt is increased, there are marked deviations between z(0) and D-0. The se differences between z(0) and D-0 are also related to the shape of t he single-event spectrum. This technique provides a powerful tool for relating observed cell survival to microdosimetric quantities for ther apeutic alpha-particle emitters. (C) 1996 by Radiation Research Societ y