Sublethal damage repair: is it independent of radiation quality

Sublethal damage repair in V79 Chinese hamster cells was compared using either single or split-doses of X-rays, Fermi Lab neutrons or JANUS Reactor neutrons. Survival curve data showed that split-doses resulted in net increases in survival except for JANUS neutrons. The relative magnitude of split-dose survival increases was determined from the ratio of the surviving fraction after a split-dose exposure to that after an equal single dose. When these ratios were plotted as a function of the single-dose surviving fraction, it was evident that split-dose survival increases were largest for X-rays, less for Fermi Lab neutrons, and not detectable for JANUS neutrons. When the ratios were also plotted as a function of total dose for the 3 different radiations, the curves showed that after X-rays and Fermi Lab neutrons, cells appeared able to repair radiation damage to approximately the same degree. Little if any survival increase was observed after JANUS neutrons. The implications of possible partial cell synchronization resulting from the first doses and LET-dependent effects on the rates of ageing of cells surviving first doses were also discussed in relation to the present results. (UK)