Functional and morphological changes in pig skin after single or fractionated doses of X rays

The flank skin of pigs has been treated with either single or fractionated doses of x-irradiation. A single dose (2070 cGy) was compared with treatment given as 6 fractions in 18 days ($\text{6}\text{f}\text{18}$ days; 3780 cGy) or 30 fractions in 39 days ($\text{30}\text{f}\text{39}$ days; 8000 cGy). The doses were selected on the basis that similar levels of late tissue damage would result. Radiation induced changes in the skin were assessed by observing the skin reactions and by the measurement of isotope clearance (functional study), relative field contraction, dermal and epidermal thickness and dermal vascular density (morphological studies). In the three treatment groups the early radiation reaction varied considerably. In the first wave reaction (3 to 6 weeks after treatment) bright red erythema was recorded in many fields but moist desquamation developed only in the $\text{30}\text{f}\text{39}$ days treatment group. The second wave (10–16 weeks) was characterized by an ischemic mauve/dusky reaction. Dermal necrosis developed in 50% of the single dose fields. In the $\text{30}\text{f}\text{39}$ days regimen persistent moist desquamation progressed to dermal necrosis. Neither desquamation nor necrosis developed after $\text{6}\text{f}\text{18}$ days. Different levels of vascular damage in the dermis were assessed using an isotope clearance technique; for example in the early reaction significant changes were recorded in the papillary dermis (faster clearance) prior to the development of moist desquamation ($\text{30}\text{f}\text{39}$ days) and in the reticular dermis (slower clearance) before necrosis (single dose). Changes in clearance rates have been correlated with changes in the vascular density and thickness of the dermis. Between 26 and 52 weeks (the late reaction) relative field contraction was slightly greater in the $\text{30}\text{f}\text{39}$ days group than in the other treatment groups. Isotope clearance was similar to that in normal skin, as was the vascular density of the dermis. The return of these parameters to normal was correlated with the development of dermal atrophy.