Repair of radiation-induced damage to bone marrow cells as judged by the effect of dose rate and dose fractionation on marrow cellularity and survival of CFU/sub S/: Application to bone marrow transplantation (BMT)

The authors examined the recovery of the bone marrow of mice at three TBI dose rates (47, 25 and 8 cGy/min). The radiation response of CFU (D/sub o/=70 cGy, D/sub q/=20 cGy) and marrow D/sub o/=130 cGy, D/sub q/=85 cGy) was independent of dose rate. One TBI dose fractionation scheme was chosen: two fractions per day, separated by six hours, for three days. The effect of dose fractionation on marrow cellularity was marked in that the D/sub o/ was increased from 130 cGy (single fraction) to 300 cGy (all dose rates). The radiation survival curve of CFU/sub s/ showed a D/sub o/ of 110 cGy (all dose rates) compared to 70 cGy for the one fraction case (D/sub q/ was unchanged at 20 cGy). The implications of these observations, as they pertain to BMT, are discussed together with how this repair is modified by the use of 2 daily doses of Cytoxan prior to the fractionated TBI