The tolerance of mouse tails to necrosis after repeated irradiation with X rays

Abstract

The reduction in the tolerance dose for the production of tail necrosis in adult mice 7 wk after irradiation was measured in tails which had previously received various single or multiple tolerable doses. The ability of heavily-irradiated and healed tails to tolerate about a further 90% of the first dose was found to apply between 6 wk and 10 mo. after the first irradiation. The tolerance dose was reduced to about 65% of the original at the 3rd irradiation and this dose (approximately) remained tolerable at the 4th, 5th and 6th irradiation, all delivered at 6 wk intervals. Subsequent to 7 wk after the 6th dose, late effects were observed as an atrophy of the tail, mostly distal to the healed irradiated region. The occurrence was very marked (occurring in about 40% of tails by 8 mo.) compared with that observed after only one dose (nor more than 4% by 8 mo.) Hence, if the assay time was extended to 8 mo. after irradiation to include these late effects, the tolerance dose for the tail after the 6th dose would be reduced further to about 55% of the original value.