Nanodosimetry: Bridging the gap to radiation biophysics

Nanodosimetry strives to link phenomenological dosimetric concepts like radiation quality and relative biological effectiveness to measurable physical quantities related to the track structure of ionising radiation. The ultimate goal of nanodosimetry is therefore to determine novel dosimetric quantities that include the initial biological or biophysical action of ionising radiation. As a step towards this, experimental and numerical techniques have been developed to characterise particle track structure based on the formation of ionisation clusters within a target volume comparable in mass per unit area to a DNA segment. Several attempts have been made to connect the nanodosimetric parameters derived from these ionisation cluster size distributions to biological radiation effects.This work gives an overview of the basic aspects of nanodosimetry, including a discussion of two nanodosimetry-based approaches used to derive estimators of biological effectiveness of ionising radiation. It also includes preliminary results from an ongoing Monte Carlo study into the limitations of using the physical properties of liquid water to approximate those of DNA in nanodosimetric modelling. The findings suggest an overestimation of radiobiological effectiveness may occur when the cross section data for liquid water are used as a substitute for those of DNA.