[Effects of low-dose total body irradiation (TBI) on tumor-bearing rats]

To investigate the anti-tumor effects of low-dose total body irradiation (TBI) histologically, 5 x 10(5) KDH-8 cells were implanted into the right legs of WKAH rats. According to the treatment policies, rats were divided into four groups: non-treated, TBI alone, local irradiation (LI) following TBI, and LI alone. The total dose of TBI was 0.2 Gy, that of LI 10 Gy or 0.2 Gy. Local irradiation of 0.2 Gy had no suppressive effect on the growth of implanted tumor and/or metastasis. In the 10 Gy LI group, growth of the implanted tumor was totally suppressed, and histological findings (H-E staining) showed that there were few viable cells, few tissue-infiltrating cells, and severe fibrotic changes in the tumor tissue. In the TBI group, tumor growth was suppressed during only 7 days after TBI. However, abundant tumor infiltrating cells appeared 24 hours after TBI. Total body irradiation did not enhance the suppressive effect of LI on tumor growth. Metastases of the lung and abdominal lymph nodes were significantly suppressed by TBI. In the TBI group, using the lung-shield with 5 cm lead block, the suppression of lung metastasis was the same as that in the non-shield TBI group. These results suggested that a low dose of TBI brings about anti-tumor effects through a host immune response, unlike those produced by high-dose irradiation.