What is the relevance of repair and time between fractions in multiple daily fractions per day radiotherapy (MFDR)?

Abstract

The impetus for these experiments was due, in part, to the palliation noted by the author using two fractions per day to treat patients with osteogenic sarcoma and to the lack of agreement, in the literature, on the optimum fractionation of total body irradiation in the preparation of patients for bone marrow transplantation (Evans, 1983). We chose to use plateau-phase cultures as we believe this system represents a reasonable in vitro tumour model (80% of cells in G1-like phase) (Hahn & Little, 1972). In addition we measured the magnitude of the repair of potentially lethal (RPLD) and sublethal damage (RSLD) in balanced salt solution (HBSS) in the belief that these conditions simulated the milieu existing in a tumour. (We hasten to add that the term “repair” is used in an operational sense and is not meant to imply any knowledge of the biochemical modification of damaged DNA). Although mammalian plateau-phase monolayers are a convenient test system we are fully aware that they do not share many of the properties of tumours; including response as a function of tumour size, regions of hypoxia and ability to reoxygenate.