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Decreased Tumor Uptake of Gallium-67 in Animals after Whole-Body Irradiation

W. P. Bradley, P. O. Alderson^*, W. C. Eckelman, R. G. Hamilton and J. F. Weiss

Armed Forces Radiobiology Research Institute, Bethesda, Maryland

Correspondence: For reprints contact: William P. Bradley, Biochemistry Dept., Armed Forces Radiobiology Research Institute, Bethesda, MD 20014.

ABSTRACT

The mechanism of decreased Ga-67 citrate retention and serum binding after whole-body irradiation is unknown. To investigate this mechanism and to determine the effects of prior irradiation on tumor uptake of Ga-67, Sprague-Dawley rats bearing a subcutaneous Walker-256 carcinosarcoma were exposed to whole-body Co-60 irradiations of 250–1000 rads. Each animal received 10 µCi of Ga-67 citrate intravenously 24 hr after exposure. Control animals received Ga-67 but were not irradiated. Animals were killed at 48 hr and the uptakes (percentage ID/g) in the tumor and other tissues were determined. A blood sample was also obtained to determine the serum iron, unsaturated iron-binding capacity (UIBC) and transferrin level. Tumor uptake and serum UIBC were decreased in irradiated animals, whereas serum iron levels and Ga-67 urinary excretion were increased. There was a significant correlation between the UIBC and the Ga-67 tumor uptake (r = 0.78, p < 0.001, n = 49). Transferrin levels in the irradiated group were not different from control values. The results indicate that the decreased Ga-67 retention and tumor uptake seen after whole-body irradiation are related—at least in part—to the saturation of transferrin by increased levels of circulating iron.

FOOTNOTES

^* Current address: Johns Hopkins Hospital, Baltimore, MD 21205.

Visiting Investigator, AFRRI. Address: George Washington University, Washington, D.C.