Response of murine bone marrow CFU-S and GM-CFU-C to irradiation in vivo at different dose-rates

Murine bow marrow was treated in vivo with acute irradiation (1.5Gy/min) and and the survival of two cell populations was measured (CFU-S, GM-CFU-C0. The survival curve for CFU-S was exponential (D/sub o/=1Gy, n=1), whereas that for GM-CFU-C displayed a small shoulder (D/sub o/=1Gy, n=4). This difference in survival parameters was further demonstrated by response to split dose irradiation. For CFU-S there was no recovery between doses whereas a recovery ratio of 4 at 4h was seen with GM-CFU-C. It has been suggested that ultra-low-dose-rate irradiation leads to the expression of only the irreparable component of radiation damage, i.e. repair is complete. Therefore cells which have no shoulder to their acute radiation survival curve would not be expected to exhibit a dose-rate dependent change in radiosensitivity. The authors' data support this, the CFU-S survival curve was unchanged even at dose-rates as low as 0.167cGy/min, while for GM-CFU-C, the survival curve became exponential (D/sub o/=1.6Gy, n=1) at dose rates below 0.5cGy/min