Letter: Fractionation schedules and a quadratic dose-effect relationship.

Your correspondents Bengtsson and Lindborg (1974) refer to earlier attempts to relate biological effects following fractionated irradiation to a quadratic dependence on dose(Gray, 1944; Fowler and Stern, 1960; Kellerer and Rossi, 1971). We have fresh experimental evidence that such a relationship may indeed be relevant. Recent experiments in our laboratory, designed to elucidate the conflict in predictions of total dose required to produce a given biological effect between Dutreix, Wambersie and Bounik (1973) and Ellis (1969), have indicated a simple relationship between total dose and size (or number) of each fraction of low-LET radiation.