[Influence of radiation doses in local radiotherapy on anti-tumor immunity and tumor metastasis].

The relationship between radiation doses and the subsequent metastasis formation after local radiotherapy against a rat transplantable fibrosarcoma was studied. KMT-17 fibrosarcoma cells were transplanted into the hind leg of syngeneic WKA rats and the leg were irradiated with various doses of 60Co gamma-rays 5 days after the tumor transplantation. 97% of the local primary tumors regressed in the rats received more than 45Gy (high dose-group), whereas only 41% of the tumors regressed in the rats received less than 40Gy (low dose-group). On the other hand, the percentage of the subsequent metastasis in the high dose-group was significantly higher than that of the low dose-group. By Winn's assay, stronger tumor-neutralizing activities were observed in the spleen cells of rats received 30Gy than those of non-irradiated rats or rats received 60Gy. The above results suggest that the low dose irradiation to the local tumor stimulates the anti-tumor immunity which results in suppression of the tumor metastasis.