Skin tolerance to fractionated X-irradiation in the pig- how good a predictor is the NSD formula?

Abstract Fields on the flanks of domestic swine were irradiated with 250 kVp X rays in courses of one, six, or 30 fractions. The acute skin response was scored quantitatively using a numerical scheme. Late skin tolerance, up to one year after exposure, was determined by the presence or absence of skin necrosis in the irradiated fields. The Nominal Standard Dose was a poor predictor for early skin response; an approximately 30 per cent higher equivalent dose was required when administered in six fractions over 18 days to produce either dry or moist desquamation, than was required when given in 30 fractions over 39 days. The difference was even greater when compared with single radiation doses. Late skin tolerance was not closely correlated with the level of early response, but skin necrosis was well predicted by the NSD formula. These data in the pig correlate well with clinically determined late skin tolerance in three large radiotherapy centres. For a 64 cm2 skin field, however, skin tolerance in the pig...