Absorbed dose-an irrelevant concept for irradiation with heavy charged particles?

Abstract

The recent (1991) issue of ICRU News contains a draft report by members of ICRU on quantities and units for use in radiation protection. It follows the traditional path of taking absorbed dose as the fundamental quantity and deriving a series of other quantities related to it. The purpose of the present communication is to query whether such an approach is really relevant for heavy charged particles. Problems arising from trying to decide on the appropriate quality factors are discussed, and microdosimetric investigations which show the weakness of 'averaging' implied by dose are reviewed in some detail. It is proposed that, instead of dose, fluence should be adopted as the fundamental quantity for use in radiation protection. This would have the very great advantage of being the quantity actually registered by a measuring instrument. Linked to this, the idea of 'hit size effectiveness', originally proposed by Bond et al. (1982,1985), could be used to quantify tissue responses.