GENERALIZED MICRODOSIMETRIC CALCULATIONS OF CELL-TO-CELL VARIANCE

The cell-to-cell variance of an endpoint gives extra information, whic h is highly model dependent and thus potentially useful for distinguis hing between possible mechanisms. Some years ago, Virsik and Harder ca lculated variances of dicentric chromosome aberrations using two assum ptions: first, that dicentrics are produced independently by different radiation tracks, and second, that the dicentric yield due to a singl e track is Poisson distributed. It is shown that the formalism can be generalised so that the Poisson assumption is dropped. This affects pr edictions of neutron induced variances quite markedly. For lesions for med directly, such as immediate, irremediable chromosomal breaks, the formalism is general. For lesions formed by pairwise damage interactio n, such as exchange-type chromosomal aberrations, the first assumption (single track action) limits the applicability of the results to high LET or low dose situations. In general, therefore, estimating varianc es requires the use of spatially inhomogeneous models.