Effect of Post-irradiation Incubation Conditions on Recovery between Fractionated Doses of X-rays

Abstract

ELKIND¹ first demonstrated the ability of mammalian cells to recover rapidly from sub-lethal X-ray damage so that a second radiation dose delivered after an interval was less effective in reducing cell survival than the same total dose delivered as a single exposure. The recovery had a clearly defined structure with a rapid decrease in the effect of a second dose delivered 1–3 h after the first followed by a return towards full efficacy if the interval was 5–8 h, and a second more permanent recovery (called ‘repair’ by Elkind) which was completed prior to the first post-irradiation cell division. This rapid recovery has been confirmed in vitro and in vivo in a wide variety of mammalian cell types^2–5, and a similar process has been observed in at least one plant system⁶. The experiments described here were designed to test whether recovery was dependent on the metabolic state of the cell and hence subject to alteration when the conditions of incubation between radiation exposures were altered.