Repopulation in mouse oral mucose: changes in the effect of dose fractionation

Purpose: To define the fractionation effect, including the magnitude and ki netics of dose compensation, on days 3 and 8 after a single priming dose of 8 Gy. Materials and methods: Graded radiation doses were given to the snouts of C 3H/Neu mice in 1 to 5 fractions within a time period of less than or equal to 36 h, or in four fractions with intervals from 5 min to 4 h. Each protoc ol was terminated by a top-up dose of 2.5 Gy to a 3 x 3 mm(2) test area in order to precipitate the subclinical damage induced by the snout treatment and to generate the full dose response. Results: No significant increase in isoeffective dose by increasing Fractio n numbers or by increasing interfraction intervals could be detected at eac h time point after the priming treatment. This indicates that the effect of dose fractionation was entirely lost. Conclusions: The loss of fractionation effect may be interpreted as a subst antial impairment of the processes underlying recovery from sublethal damag e as a consequence of a repopulation-inducing priming dose given 3 days or 8 days in advance.