Prediction of biological radiation effects based on ionization clusters (nanodosimetry)

Abstract

This article reviews approaches that link the formation of ionization clusters in nanometric volumes to radiobiological effectiveness. The corresponding models are presented using harmonized terminology and notation. They are categorized into three classes according to the most important, often implicit model rationale: (a) models that use a nanodosimetric weighting factor for biological effectiveness derived from frequency distributions of ionization clusters in a single target; (b) models that account for the synergistic effects of pairs of ionization clusters formed in different targets; (c) models that account for 'macroscopic' situations involving many nanometric targets and derive radiation quantities from the particle fluence. Further conceptual differences between the models and their underlying assumptions are discussed, such as the fact that some models are mechanistic while others only aim to elucidate correlations. Eventually, an attempt is made to identify the key open questions in this field that still need to be addressed.