Concepts of Microdosimetry and their Applicability to DNA Studies

Abstract

Ionizing radiations differ from other genotoxic agents by producing, in addition to point mutations, a disproportionate frequency of deletions and other complex DNA lesions. This special characteristic reflects the spatial correlation of energy deposits within the tracks of ionizing charged particles. In the tracks, even of sparsely ionizing particles, clusters of ionizations occur and local concentrations of free radicals that would be extremely unlikely for a uniform random distribution of energy and that could be expected only at doses that are far too large to be of biological relevance. The microscopic correlations of energy deposits are also the reason for the fact that the yield of DNA lesions is proportional to dose - except at very high doses - and that any deviation from linearity must be the expression of energy transport or lesion interaction over comparatively large distances of fractions of a micrometer or of a dose dependent change of repair efficiency.

Microdosimetry provides the concepts that are required to quantify the microscopic spatial correlation of energy deposits for radiations of different quality and to link them to the spatial distribution of the resulting DNA lesions. The basic concepts and quantities are explained, and examples are given that can be related to the size of the DNA structures and to critical distances for the production of DNA lesions.