Swine basal cell proliferation during a course of daily irradiation, five days a week for six weeks (6000 rad)

In swine skin irradiated with 200 rad per day, 5 days per week for 6 weeks, basal cell density remained at control levels for the first 2 weeks and then decreased to a nadir of 50% at 38 days. Thereafter it began increasing and returned to near control levels within 1 day after the end of irradiation on day forty-three. The mitotic index increased progressively to a maximum value three times the controls at day forty-two and then decreased as the cell density returned to control levels. The pattern strongly suggests that cell proliferation occurred during the period of irradiation. The cell density changes are simulated by a model in which doubling time switches from 12 days to 2.5 days at the 50% cell density level.