Abstract

We examine, as a function of a particle type and energy as well as the geometrical configuration of the sensitive site, the extent to which a description of the track in terms of itsradial dose distribution can be used as a substitute for a full microdosimetric description. The critical parameter appears to be the ratio between the site diameter and the maximum lateral extension of the track (penumbra): whenever this ratio is significantly larger than 1 the radial-distribution-derived microdosimetric spectrum is accurate. While in general, for ratios smaller than 1, the spectra thus calculated are not correct, one can obtain significant improvement by considering tracks of restricted radial extent (yet comprising most of the delivered dose). In terms of a microdosimetric-based quality factor the radial dose distributions generally lead to correct estimates.

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