Radiation Dose Fractionation and DNA Replication

IT has been shown that the magnitude of depression of DNA synthesis following radiation can be altered by altering the dose-rate 1 . These preliminary results suggest that the total dose alone may be inadequate in the assessment of the effects of radiation on DNA synthesis. Dose-rate and the duration of radiation are additional factors which might be needed for an adequate assessment of the effects of radiation on this key biological process. This investigation was carried out on a synchronous population of hepatocytes, near the mid-point of the 8-h replication period following partial hepatectomy. A subsequent investigation was made into the dependence of DNA depression on dose-rate both in synchronous liver cells and in asynchronous cells of the first part of the small intestine 2 . These two series of experiments have permitted comparison of the effects of localized radiation on DNA synthesis both in synchronous liver cells and in asynchronous intestinal cells in the same animal. The curves describing the depression in the two organs were similar in character; however, the magnitude of the depression in the intestines, initially, was greater than in the liver.