EXPLOITABLE RADIOBIOLOGICAL MECHANISMS IN RADIOCHEMOTHERAPY

Background: The radiobiological mechanisms which may be exploited in t he design of new strategies of radiochemotherapy are discussed. Method s: The identification of exploitable mechanisms of radiochemotherapy h as to be based on the analysis of cellular and supracellular mechanism s of tumor cure, acute normal tissue injury and chronic normal tissue injury, respectively, as well as on experimentally documented mechanis ms of cellular and supracellular interactions of chemotherapy and radi otherapy. Results: Only the addition of independent cytotoxic effects of radiotherapy and of chemotherapy are a sound basis for predicting t he therapeutic effects on tumor cure probability. In the pathogenesis of normal tissue damage, however, complex interactions of supracellula r mechanisms play a decisive role which may increase the rate of chron ic side effects even in the absence of cellular interactions. Conclusi on: None of the presently used schedules of radiochemotherapy meets th e scientific requirements outlined in the paper. For squamous cell car cinomas the most promising protocol would combine effective doses of c hemotherapy and of radiotherapy without dose reduction and/or treatmen t prolongation simultaneously but without causing increased normal tis sue injury.