Quantification of radiation-induced epilation in the pig: a biological indicator of radiation dose to the skin.

Epilation in the pig has been quantified following single exposures of X-rays in the range 1.0-25.0 Gy. The number of hairs in each field was determined by counting hairs from photographic negatives weekly for 10 weeks following irradiation, and the percentage hair loss was calculated for each individual field from an initial unirradiated control value. Hair loss was dose-dependent for exposures between 1.0 and 15.0 Gy and this response was linearly related to dose. No further increase in hair loss was observed for doses > or = 15.0 Gy, as 20-30% of the hairs remained. It was assumed that these hairs were not actively growing at the time of irradiation and did, therefore, not express damage. The ED50 for the loss of > or = 30% of hairs was 3.8 Gy whilst that for the loss of > or = 50% of hairs was 6.8 Gy and for the loss of > or = 67% of hairs was 12.5 Gy. There was +/- 7% hair loss per Gy exposure for doses between 0.0 and 15.0 Gy. Quantification of hair loss provided a more sensitive assay than the use of visual scoring systems. Hair loss was detectable within 4 weeks of irradiation. The system is simple, non-invasive and appears to have considerable potential for use as a biological dosimeter.