Recovery and Repopulation in Mouse Skin after Irradiation with Cyclotron Neutrons as Compared with 250-Kv X-Rays or 15-Mev Electrons

Abstract

In a previous publication, Fowler et al. (1) discussed the short-term recovery of mouse skin after 15-Mev electron irradiation, the recovery being measured in terms of the parameter D2 D1, where D2 is the total dose given in two fractions to produce the same biological effect as a single dose, D1. For mammalian cells in tissue culture and in vivo, the magnitude of the recovery from sublethal damage as described by Elkind and Sutton (2) has been shown to be smaller after high-LET irradiation (3-6). Using an intact mammalian system (the survival of mice for more than 4 days after single or split doses of cyclotron neutrons or X-rays), Hornsey et al. (7) found a small value of D2 D1 after neutrons, but a relatively large value after X-rays. Previous work with pig skin had, however, shown the short-term recovery after fast neutrons to be about two-thirds that after X-rays, allowing for RBE (8). In the present paper the mouse skin system is used to compare the results of fast neutron irradiation with those of 250-kv X-rays and 15-Mev electrons. The work may be divided into two parts. The first consists of a comparison of the time of appearance of skin reactions, their rate of increase, and their subsequent rate of decrease, after fast neutron as compared with X-ray or 15-Mev electron irradiation. The skin reactions observed are presumed to be due to epithelial cell depopulation, so that the rate of decrease of the skin reaction is taken as a measure of the repopulation rate of epithelial cells (19). The second part consists of the investigation of the magnitude (and rate) of the short-term recovery in mouse skin, measured by the dose increment D2 D1,