Distribution of radiolabeled cis-diamminedichloroplatinum (II) on scintigraphic images in the tumor-bearing rabbit.

To evaluate the feasibility of using scintigraphic images to assess the distribution of cis-diamminedichloroplatinum (II) (CDDP), we obtained serial scintigraphic images using radiolabeled CDDP (Pt-195m CDDP), which had high specific activity (7.4 x 10(6) Bq [200 microCi]/mg-CDDP) in the rabbit VX-2 tumor system. Radioactivity at the heart decreased in a biexponential manner, with an initial half-time of 15.3 min and secondary phase of 4.5 days. Time-activity curves revealed that the tumor/heart ratio was greater than 1.0 (1.0-1.1) between 30 min and 4 hr after intravenous injection. The scintigraphic study clearly depicted the tumor. Pt-195m CDDP uptake by the rabbit tumor at 2 hr was 7.8% of the total injected dose. These data suggest that scintigraphic imaging using Pt-195m CDDP is a promising method for imaging tumors and evaluating their CDDP uptake.