Measurements of in vivo effects of an electron-affinic radiosensitizer using a double tracer technique.

In sarcoma-180 of NMRI mice, euoxic tumour cells were labeled with 131I-iododeoxyuridine, and the average tumour cells were labeled with 125I-iododeoxyuridine. An external counting technique permitted in vivo measurements of radiation effects on rates of loss of incorporated activity from the different labeled tumour areas. The technique was employed to study the effect of tumour exposure to gamma irradiation with and without chemical radiosensitization by misonidazole (La Roche 07-0582). Injecting 500 mg/kg of Ro-07-0582 15 minutes before irradiation reduced the measurable oxygen effect by a factor of 1.54. The dose modifying factor evaluated from the 50% tumour regression at 100 days was 1.57.