CHANGES IN THE RADIATION SENSITIVITY OF MOUSE SKIN DURING FRACTIONATED AND PROLONGED TREATMENTS

Reactions of the skin of the right thigh of mice were used as an exper imental model to test possible changes in the radiosensitivity of mous e skin, as represented by changes in the linear-quadratic (LQ) model p arameters alpha and beta, as a function of fractionation interval and overall treatment time. In the first series of experiments, variable n umbers of 3-Gy fractions with intervals of 6, 24 or 48 h were applied, followed by top-up doses to increase the skin damage to a level that could be scored. The results showed that mouse skin is more sensitive to 3-Gy fractions applied with 48-h intervals than to 3-Gy fractions a pplied with 6- or 24-h intervals. In the second series of experiments we used single-dose or fractionated test treatments for previously uni rradiated mice and mice treated with priming doses of 10, 20 or 30 Gy given 1-18 days before the test treatment. The sensitivity appeared to be higher after intervals of 14-18 days than after 1-10 days after pr iming treatments of 20 and 30 Gy. The increased sensitivity 18 days af ter 20 Gy was mainly the result of an increase in the beta component o f the LQ model; higher values of alpha were also determined. We conclu de that the radiosensitivity of mouse skin is higher during a radiatio n-induced proliferative response.