Repopulation in irradiated pig skin: late versus early effects

In the first 16 weeks after irradiation, two distinct waves of reaction can be observed in pig skin, the first wave (3-9 weeks) represents the expression of damage to the epithelium while the second is indicative of primary damage to the dermis, mediated through vascular injury. Comparison of single doses with two equal doses separated by 28 days produced a D2-D1 value of 14.0 Gy at the doses which produced moist desquamation in 50% of fields (ED50) after strontium-90 irradiation. After X-irradiation, comparison of ED50 doses for the later dermal reaction suggested a D2-D1 value of 4.2 Gy. These values of D2-D1 for epithelial and dermal reactions in pig skin were compared with earlier data from this laboratory for similar split-dose experiments with a one-day interval. Such a comparison allowed for the estimation of the component of recovery in the present 28-day interval experiments due to repopulation. This component was found to be 6.5 Gy for the early epithelial damage, but was zero for the later dermal damage. (Auth.)