The optimum time for irradiation relative to tumour concentration of hypoxic cell sensitizers

It is shown that for some radiosensitizers peak tumour levels occur before the time of maximum radiosensitivity of the tumour. Kinetics and radiosensitization by misonidazole and a new drug SR - 2555 are compared. For the former peak concentration occurred 30 min post injection and maximum radiosensitization 60 min after injection. For the latter the times were 10 min and 20 - 45 min respectively. Irradiation 10 minutes after injection gave significantly poorer radiosensitization than after 20-45 mins. The relevance of the results to testing of new sensitizers is discussed. (U.K.)