The effect of a hypoxic cell sensitizer on cancer radiotherapy: an analysis by a model.

Misonidazole has been studied for its sensitizing effect of radiation on hypoxic cells in vitro and in vivo. However, clinical trials have not always shown improvement of cure rate in radiotherapy. The enhancement ratio when irradiation was performed with misonidazole was analysed by a model to examine the effectiveness of misonidazole, considering the hypoxic fraction in cancer and reoxygenation. It was shown from this model that misonidazole should be effective for cancer which had a hypoxic fraction of more than 10%, and in which reoxygenation did hardly occur, and that the effect of misonidazole was not dependent on the size of dose per fraction for radioresistant cancer.