ABSTRACT
The dose–effect relationships for cellular endpoints measured for different radiations have different shapes and different relative effectiveness. For example, acute exposure to sparsely ionising radiations results in linear–quadratic dose–effect curves but acute exposure to densely ionising radiations results in linear dose–effect curves. Traditionally, the differing biological efficiencies of different radiations have been measured by defining the relative biological effectiveness (RBE) as the ratio of the dose of a standard radiation to the dose of the test radiation which caused the same biological effect: RBE=Dose standard radiation/Dose test radiation. The deoxyribonucleic acid (DNA) double helix presents a well-defined three-dimensional target for the induction of a double strand break in the passage of a single ionising particle. Consequently, the quantitative appreciation of the biological effectiveness of different radiations makes use of the three-dimensional structure of the DNA double helix target and a theoretical description of the spatial energy deposition pattern of the radiation track at a nanometre resolution in three dimensions.
