[Radiosensitization by oxygen in Ehrlich tumor receiving artificial blood substitute (FOB 20%)]

To enhance tissue PO2 of radioresistant hypoxic cells of tumor, artificial blood substitute (FOB) was applied, because it is excellent solvent for oxygen and allows the blood circulation system to recover and consequently increase the oxygen supply from blood to the tissue. When trasplanted Ehrlich tumor of mice on thigh grew about 1,000 mm3 in volume, those were divided into three groups, group 1: 60Co gamma-ray irradiation alone, group 2: irradiation under breathing oxygen, and group 3: irradiation under breathing oxygen after exchange transfusion with FOB. The radiosensitization of FOB was studied by comparing with the OER values of three groups for 50% TGD time, 50% SD time, and 50% and 75% TCP. The OER values of 50% TGD time, 5, 10 and 50% SD time 10 of oxygen group were 1.46, 1.29, and 1.22, respectively, and oxygen effect was observed in this group. Those values of FOB group were 2.02, 1.56, and 1.56, respectively and oxygen effect of FOB group was greater than those of oxygen effect of FOB group was greater than those of oxygen group. Animals receiving FOB were apparently radiosensitized by oxygen against animals breathing oxygen at small doses irradiation effect (50% TGD time, and 50% SD time). The OER values of 50% and 75% TCP at 30 days and 90 days after irradiation of oxygen group were about 1.5 (1.46-1.61) and these of FOB group about 1.3 (1.15-1.38). Radiosensitization by oxygen of animals receiving FOB was not clearly recognized against animals breathing oxygen in TCP effect at high dose irradiation. These results indicate that radioresistant hypoxic cells of tumor receiving artificial blood substitute (FOB) increase the sensitivity of 60Co gamma-ray irradiation, especially at small dose irradiation.