Recovery and Repopulation in Vivo by Mouse Skin Epithelial Cells during Fractionated Irradiation

Abstract

The dose survival and regeneration characteristics of irradiated mouse skin epithelial cells were studied using an in situ, in vivo cell cloning technique. The cells surviving a first dose of X-rays are characterized by 24 hr. later by a survival curve having the same slope as that for cells not previously irradiated. The value for (D2-D1)24hr. was about 350 to 375 rads. The value of (D2-D1) increased by an average of about 100 rads/day with extension of fractionation intervals from 1 to 6 days. At intervals of less than 24 hr., a typical fluctuating pattern of recovery was observed. It is postulated that some repopulation by surviving cells occurs within 24 hr. of a first dose of less than 800 rads and that this proceeds in the 5 days thereafter with a doubling time for the clonogenic population of approximately 22 hr. Evidence is presented for the differentiation of about 25% of each generation of cells during rapid re-epithelialization.