The Use of Microdosimetric Moments in Evaluating Cell Survival for Therapeutic Alpha-Particle Emitters

In evaluating the efficacy of α-particle emitters, a cell survival curve is often determined for a particular source-target configuration. Investigators often wish to use this information about survival for a different source-target configuration which might be more appropriate for a therapeutic application. Since the population cell survival parameter, D 0 , is a function of the source-target configuration, it is important to determine the individual cell survival parameter, Z 0 , which is more fundamental. Unlike D 0 , Z 0 does not depend upon the microdosimetric variations in the specific energy distribution resulting from changes in the source-target configuration. Instead it is determined by the cell sensitivity and the radiation quality. However, the calculation of Z 0 from the data on survival involves computing the microdosimetric specific energy distributions of the radiation. This paper describes an approximate but sufficiently accurate method for determining Z 0 from D 0 if the first and second moments of the single-hit specific energy distributions are known or can be estimated. Examples of applications are given. This may alleviate the need for multihit microdosimetric calculations.