Radiation research
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We performed two independent series of experiments aiming at establishing dose-response curves for lethality or oncogenic transformation in vitro following acute and protracted X-ray doses between 0.25 and 2 Gy. In the first series of experiments, we measured the survival of C3H/10T1/2 CL8 fibroblasts and their transformed counterparts (MCA TCL15) as a function of X-ray dose delivered at 0.49 Gy/min. In addition, 1- and 2-Gy doses were split into four fractions separated by 3-h intervals. ⋯ The dose-response curves for oncogenic transformation in the low-dose range between 0.25 and 2 Gy were consistent with a linear response with a positive slope 2.50 +/- 0.11 X 10(-4), 1.50 +/- 0.03 X 10(-4), or 0.87 +/- 0.05 X 10(-4) Gy-1, for acute, 1-h, or 3-h protracted exposures, respectively. Hence, relative to the acute irradiation, the 1- or 3-h protraction of the X-ray dose reduced the slopes by 0.60 +/- 0.03 or 0.35 +/- 0.03, respectively. These results indicate that in the dose range between 0.25 to 2 Gy, the dose-response curves for survival or oncogenic transformation were linear and can be modified by the temporal distribution of the X-ray dose.