Residual radiation-induced injury in dermal tissue: implications for retreatment

Evidence for residual radiation-induced injury was investigated in dermal vascular/connective tissue of pig skin at intervals of 17-52 weeks after irradiation. Primary irradiation was a single dose of 18 Gy. Re-irradiation was with graded single doses of X rays to establish dose-effect relationships for incidence of late ischaemic dermal necrosis of the skin; dose-effect curves obtained for previously irradiated skin were compared with those obtained using previously unirradiated skin. At intervals of 17, 35 and 52 weeks after primary treatment, ED50 values for dermal necrosis were not significantly different from those obtained for previously unirradiated skin, suggesting little or no effective residual injury at these intervals after a primary full ''tolerance'' dose. This was supported by the latency times for development of dermal necrosis, which were similar in re-irradiated and previously unirradiated skin. Epithelial desquamation was not induced by doses used in these studies, either after primary treatment or re-irradiation; however, early erythema reactions seen in re-irradiated skin were markedly reduced, particularly when carried out after 35 and 52 weeks, compared with skin not previously irradiated. (author)