Changes in the cell kinetics of pig epidermis after repeated daily doses of X rays

Changes in the proliferation kinetics of the pig epidermis were studied after irradiation with a dose fractionation regime routinely used in radiotherapy (30 fractions in 39 days). Total X-ray doses of 52.3 Gy, 61.5 Gy, 70.7 Gy and 80.0 Gy were used. Irradiated epidermis exhibited an initial degenerative phase, during which the rate of cell depletion was independent of dose. In the fourth week of irradiation, repopulation was evident in the 52.3 Gy and 61.5 Gy dose groups. At higher doses, cell loss continued, with epidermal denudation by the end of irradiation. The severity and cell depletion and the rate of recovery of the epidermis was dose-dependent. The regenerative phase was characterised by increased cell proliferation. Labelling index values were elevated above those in the normal, non-irradiated epidermis, from four weeks until the end of irradiation. Changes in this parameter were independent of dose. No change in the DNA synthesis time was found. At the end of irradiation, islands of cells (colonies), with an appearance similar to cells in normal epidermis, were seen, and the cell turnover time for the proliferating cells of the basal layer in the irradiation-damaged epidermis was 48-54 h. For the cells in the colonies it was 17-22 h. (author)