Hit-size effectiveness approach in radiation protection

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.