The effect of field size on the reaction of pig skin to single doses of X rays.

The importance of the size of the treatment area for the response of the skin to radiation has been studied in the pig. The responses of skin areas of 16 cm3 (4 x 4 cm) and 64 cm2 (16 x 4 cm) were compared after single doses of X rays. In the initial 3-9-week period after irradiation the severity of the erythema reaction, which is associated with epidermal call death, was not influenced by the area of skin irradiated. For the later dermal response (10-16 weeks) a similar result was obtained. The dose required to produce dermal necrosis in 50% of the fields treated (ED50) was approximately 2070 cGy for both field sizes. Additional studies have shown that the ED50 for dermal necrosis was not influenced by the age of animals at the time of irradiation. This was despite considerable differences in the vascular density and blood flow in pig skin with increasing age. The apparent contradiction between the results of this experimental study in the pig, which shows no effect of field size, and currently accepted clinical practice is discussed.