Restricted LET Remains a Good Parameter of Radiation Quality

Abstract

Abstract A suitable physical parameter of radiation quality must represent not only the mean but also the fluctuation of the energy deposition per particle passage through that microscopic site of tissue in which proximity between radiation-induced lesions is decisive for the action mechanism. For sites of nanometre dimensions restricted LET is considered to have this property because (a) the distribution moments j and j2/j of the number j of ionisations per delta ray within the site are almost independent of the type and energy of the primary particle, and (b) the Poisson fluctuation of the number of primary ionisations within the site is determined by its mean value, which is proportional to restricted LET. Corresponding to this theoretical qualification as a suitable parameter, restricted LET has been experimentally identified as determining the yield factor a of various cellular radiation effects.