Repair and Repopulation in Mouse Skin During Multifractionated Irradiation

To study the recovery from sublethal damage and the repopulation kinetics of skin during multifractionated exposures, mouse legs were exposed to 137Cs γ rays. Levels of skin shrinkage were measured 50 to 70 days after either single or multiple fractions (up to 32) with various intervals of time between doses. The higher the dose per fraction, the later the surviving cells started to repopulate after irradiation. When the dose per fraction was 370 to 490 rads, and the number of fractions 8 to 32, the regeneration rate per day was almost constant from day 7 to day 31 after the first exposure. It was calculated that the number of skin stem cells increased an average of 1.3 fold per day. When the dose per fraction was more than 1000 rads, the average repopulation rate between day 15 and day 31 was lower than that between day 6 and day 15.