Deposition of Radiogallium (Ga⁷²) in Proliferating Tissues

It has previously been shown, chemically and autoradiographically, that gallium enters bone at a rapid rate, following injection of the citrate or lactate, concentrating in those areas considered to have marked osteogenic activity (1, 2, 3). The purpose of the present investigation was to study in experimental animals the deposition of radiogallium (Ga72) in proliferating tissues. The work comprised three parts: (a) the quantitative determination of the amount of Ga72 deposited in normal and growing bone and in healing fractures, (b) a pilot study of the degree of deposition of gallium in certain neoplastic conditions, (c) development of technics to provide greater detail in the autoradiographs of tissue containing Ga72. The isotopes of gallium which appear to have greatest promise for biological studies are Ga72 (14.3 hours half-life, 2.5 mev γ, 3.1 mev β−) and Ga67 (78.3 hours half-life, K capture, 0.3 mev γ with conversion e−). The Ga72 can be prepared by neutron bombardment of magnetically separated Ga71 to produce an initial specific activity of about 1.0 mc. Ga72∕mg. Ga. By deuteron bombardment (d, n) of a zinc target in a cyclotron, the isotope Ga67 can be produced, accompanied by a quantity of Zn65 (250-day half-life). This and other contaminants may be eliminated by ether extraction of gallium from a 6 N HCl solution. The studies described herein were carried out with Ga72 supplied by the Atomic Energy Commission. The natural element (Ga69 + Ca71) was activated by the (n, γ) reaction, and an initial activity of about 0.4 mc.∕mg. Ga was obtained. On administration to animals, the activity was reduced by decay to about 0.2 mc.∕mg. Ga. Methods Preparation of gallium (Ga72) citrate: Quartz ampules were prepared and sufficient purified gallium nitrate was added to provide 75 mg. gallium (5). These ampules were flame-sealed and irradiated in the pile by the Atomic Energy Commission. The initial activity was approximately 30 millicuries (mc.); when shipped by air, the gallium could be administered with an activity of 12–15 mc. Preparation of the gallium for injection was as follows: a. Add to the opened ampule 1 c.c, hot HCl (1:1). Heat gently to facilitate solution of the solid. Pour into a graduate cylinder, and rinse ampule with 2-c.c. portions of water. b. Add 1 c.c. of brom-cresol purple indicator. c. Add 2 c.c. of 20 per cent citric acid solution. Mix.