Fractionated dose radiotherapy and its relationship to survival curve shape

Abstract

Summary The radiobiology fundamental to rational radiotherapy is a developing, enlarging subject. This was emphasized once again by the 6th L. H. Gray Conference (London, 16–20 September 1974); a Conference addressed to the relevance of the initial part of the clonogenic and/or stem cell survival curves to the total doses and fractionation regimens required for effective radiotherapy. To indicate why the conferees focused on the initial shape of the single-cell survival curve, the essential biophysics and cell biology are reviewed from which important implications for radiotherapy can be derived. The data presented at the Conference are summarized and make it clear that generalizations relative to survival curve shape are not possible. In addition, examples are developed indicating where and how other factors may be critical to the effectiveness of fractionation. Although definitive answers were few, the 6th L. H. Gray Conference served to identify a number of points of growth needed to improve the applicability of radiobiology to radiotherapy.