Hit-size effectiveness approach in radiation protection

Abstract

Reviews the hit-size effectiveness (HSE) approach as applied to radiation protection. Topics discussed include: the rationale for the HSE method, the mathematical description of the formalism, biological end points relevant for the application of HSE in radiation protection, and theoretical and experimental methods for obtaining microdosimetric spectra. The application of HSE requires a mathematical unfolding algorithm. Of several methods proposed the authors have selected a technique based on Bayesian and maximum entropy methodology; this bias-free approach is described. By way of illustration they present a catalogue of currently available HSE functions for different end points: cellular reproductive inactivation, mutation, chromosome aberrations and neoplastic cellular transformation. In each case, the authors indicate the sensitivity of the result to the selected size of the sensitive volume, taken for simplicity as spherical. From this analysis it is concluded that the site size plays only a minor role in selecting the appropriate HSE function; it follows that practical means (e.g. microdosimetric proportional counters) are already at hand to implement the HSE formalism in radiation protection and health physics.

ICRU Report 98, Stochastic Nature of Radiation Interactions: Microdosimetry

“…Correlations between lineal energy distributions in spherical volumes in a variety of charged particle and photon fields and biological effectiveness at low absorbed doses have been sought also in terms of a hit size effectiveness factor that assumes a fixed probability of quantal biological response as a function of energy imparted in a sphere (Varma et al , 1993; 1994). Complex empirical functions were derived for sphere sizes of 20, 100, and 1000 nm by fitting to a selection of cellular effects of potential relevance to radiation risk (Varma et al , 1994).…”