Optimal fractionation for the radiotherapy of tumour cells possessing wide-shouldered survival curves

Though the radiocurability of human tumours varies widely, most cells in culture prove to have rather similar radiation survival curves. A small number of tumours, however, including melanoma (Dewey 1971; Barranco et al., 1971), osteosarcoma (van Putten 1968) and rhabdomyosarcoma (Rheinhold 1966), have been reported to possess unusually wide-shouldered survival curves for cells growing in culture.

These observations have given rise to the suggestion that there may exist a sub-class of radioresistant tumours whose resistance is due to a wide-shoulder rather than to a shallow terminal slope of the survival curve. Such tumours might be treated more effectively by a small number of large-dose fractions of radiation, than by a conventional schedule (Hornsey 1972; Wheldon and Kirk 1975). This contention is supported by the results of a recent clinical trial (Habermalz and Fischer 1976) and retrospective survey (Hornsey 1978) in the case of malignant melanoma, and by very preliminary clinical indications in the case of osteogenic sarcoma (Goffinet et al., 1975; Kaplan 1977).