Growth of Krebs-2 free tumor cells in the ascitic fluid of the mouse (CFW or albino) and their spread and implantation into peritoneal tissues were considerably reduced either by total-body irradiation (external and systemic) with 400 r or by intraperitoneal injection of 0.15 mc. of colloidal radioactive chromic phosphate (internal and topical irradiation). Combined irradiations given in either succession completely prevented (or very nearly so) invasion of the fluid accumulation. Similarly, growth and spread of tumor cell inoculated subcutaneously into the scalp were arrested partially by either method of irradiation and totally by their combination. Analogous phenomena were produced in some normal tissues: in normal mice given 0.15 mc. isotope into the scalp the spleen was enlarged by congestion; in irradiated (400 r) mice, it was slightly shrunk, and considerably shrunk after combined irradiation. It was concluded that the effect of internal (topical) irradiation on tumor cells and on blood vessels was considerably increased by combination with external (systemic) irradiation or vice versa.

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This work was supported by Grants No. AT (40-1)-1993 from the Division of Biology and Medicine, U.S. Atomic Energy Commission; No. DRG 466 from the Damon Runyon Fund; and No. C-2080 (C5) M & G from the National Cancer Institute, Bethesda, Maryland.

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