Comparative studies of radiocitrates in oncological models

67Ga citrate and sup(99m)Tc citrate (Solcocitran) were injected sequentially, with an interval of 48 h, into Balb/c mice bearing transplanted EMT-6 tumors. Tissue distributions of 67Ga and sup(99m)Tc were measured simultaneously at intervals of 1, 3, 5 and 8 h after injection of the sup(99m)Tc citrate (49, 51, 53 and 56 h after 67Ga citrate). Maximal tumor:blood ratios for 67Ga and sup(99m)Tc were 13.8+-3.2 and 4.0+-1.0 respectively, both occurring at the final period. The maximum tumor index for 67Ga was 71+-23% 56 h after injection, and for sup(99m)Tc was 13+-12% 1 h after injection. Liver, kidney and spleen had equal or higher concentrations of radioactivity than tumor for either radiotracer. The somewhat higher tumor:blood ratio for 67Ga citrate was offset by the time required for this optimum to be reached. Alternatively, the best sup(99m)Tc citrate tumor:blood ratios were attained within 8 h, with less liver and gut radioactivity. In view of the radiation dose, the inconvenience of the 48-72 h wait, and the cost of 67Ga, and because neither radiopharmaceutical is tumor specific, sup(99m)Tc citrate may have a place in early oncological screening. (author)