The relationship of acute to late skin injury in 2 and 5 fraction/week γ-ray therapy

Areas of pigs' skin were exposed to fractionated doses of y-rays, and their acute and late (several months) responses were measured as desquamation and degree of contraction, respectively. The purpose was to measure the relative changes in acute and late response when the dose fractionation pattern of a 6.5 week treatment was changed from five times to twice weekly. It was found that NSD formula did not predict isoeffect for reduced numbers of dose-fractions. Moreover, early skin response did not predict the magnitude of late damage when dose-fractionation was altered from conventional daily routines. Specifically, 200 rad five times weekly was equivalent, for acute response, to a dose greater than 435 rad twice weekly (p < 0.01), whereas, for late response, equivalence was achieved at a dose less than 360 rad twice weekly (p < 0.0526).