Recovery and Repopulation in Mouse Skin as a Function of Time after X-Irradiation

Abstract

Gross skin reactions of mouse feet have been studied after one or two doses of x-rays. For split-dose irradiations a first dose of 1000 rads was used. The total dose for various fractionation intervals to produce a chosen level of skin reaction (integrated over 8 to 30 days) was determined. The dose increment ( $D_{2}-D_{1}$ ) necessary to produce the same effect with a split dose (D2) as with a single dose (D1) was determined for the various intervals. The value of $D_{2}-D_{1}$ is interpreted as being due to (1) prompt intracellular recovery from sublethal injury; (2) progression through phases of different sensitivity in the cell cycle of cells which had been partially synchronized by the first dose; and (3) an increase in basal cell number by repopulation. The dose increment in the first 24 hours was found to be 500 to 550 rads, and a further increment of 580 rads was required from 1 to 21 days. These values are in close agreement with the results of clone-count...