Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.3
Medical

1.2.3.3
Applications -
Beneficial Effects

"Total body irradiation (TBI) has been considered to bring about immunosuppressive effects on organisms. The conclusion is derived from data obtained by sublethal doses of TBI, but there are no data on how low doses of TBI act on organisms. On the other hand, it is known that low doses of TBI are effective on some malignant lymphoma or chronic myelogenous Ieukemia. However, the effect of low doses of TBI is rarely investigated radiobiologically.

"For 15 yr, we have studied the effects of low doses of TBI on normal or tumor-bearing mice and its immunological background. ...We show the results of fundamental and clinical studies on tumor control by low doses of TBI.

"In fundamental studies, WHT/Ht mice and their spontaneous squamous cell carcinoma of C57 Black Mice and their B16 melanoma were used. Tumors were irradiated in vivo and in situ....

"We used non-Hodgkins lymphoma in clinical investigations of TBI, and immunological changes before or after TBI were checked by two-color methods.

"In the fundamental studies, the change in TD50 values in mice receiving various doses of TBI and at various hours after TBI using WHT/Ht mice and squamous carcinoma was observed. The TD5O value increases in injected tumor cells of mice at 12 h after 10 rads of TBI. The cell survival curve shows potential cell killing effects irradiating with a combined exposure of 10 rads of TBI and local irradiation, which is delivered 12 h after TBI, in spite of no cell killing effect by only 10 rads of TBI.

"In the other experiments, TBI of 10 rads demonstrates longer tumor regrowth delay and higher local control rate of tumors than with local irradiation only on tumors without TBI (Sakamoto et al 1987a, Sakamoto and Miyamoto 1987b). The TBI of 10 or 15 rads demonstrates suppressive effects on distant metastasis in a murine tumor system of the WHT/Ht strain.

"These kinds of effects are also brought about by irradiation to the spleen only; therefore, these effects may be considered to be related o immunological effects of low-dose TBI. Experimental data show that the 1L-2 response of spleen cells of tumor-bearing mice increases with 10 rads of TBI (Miyamoto and Sakamoto 1987). In clinical studies, non-Hodgkins malignant lymphoma was treated first by TBI and local irradiation. We tried to treat more than 100 patients, and 24 patients have passed the 5-yr point after treatment. Their overall survival rate, cause-specific survival rate, and disease-free survival rate are higher than for patients treated by conventional methods. The immunological examination of the patients by two-color methods resulted in increasing helper T cells, helper-inducer T cells, the ratio of active helper and inducer T cells, and the ratio of active suppressor and cytotoxic T cells (Takai et al 1991).

"The TBI is usually given to patients three times a week and a total of 150 rads is delivered to patients for 5 weeks. Hematological changes in the patients treated by TBI are not serious and are negligible. The fundamental and clinical results mentioned here briefly seem to be useful for treating malignant lymphoma by low-dose TBI."