Comparison of In-111-DOTA-Tyr(3)-octreotide and In-111-DTPA-octreotide in the same patients: Biodistribution, kinetics, organ and tumor uptake

Scintigraphy with [In-111-diethylenetriamine pentaacetic acid(0)-D-Phe(1)]- octreotide (DTPAOG) is used to demonstrate neuroendocrine and other somatos tatin-receptor-positive tumors. Despite encouraging results, this In-111-la beled compound is not well suited for peptide-receptor-mediated radiotherap y of somatostatin-receptor-positive tumors. Another somatostatin analog, [1 ,4,7,10-tetraazacyclododecane-N,N',N ",N'''-tetraacetic acid(0), D-Phe(1), Tyr(3)]-octreotide (DOTATOC), can be labeled with the p-emitter Y-90 in a s table manner. Methods: We compared the distribution, kinetics and dosimetry of In-111-DTPAOC and In-111-DOTATOC in eight patients to predict the outco mes of these parameters in patients who will be treated with Y-90-DOTATOC. Results: Serum radioactivity levels for the radiopharmaceuticals did not di ffer significantly 2-24 h after injection (P > 0.05); Up to 2 h postinjecti on they were slightly but significantly, lower after administration of In-1 11-DOTATOC (P < 0.01 at most time points). The percentage of peptide-bound radioactivity in serum did not differ after administration of either compou nd. Urinary excretion was significantly lower after administration of In-11 1-DOTATOC (P < 0.01), The visualization of known somatostatin-receptor-posi tive organs and tumors was clearer after administration of In-111-DOTATOC t han after administration of In-111-DTPAOC. This was confirmed by significan tly higher calculated uptakes in the pituitary gland and spleen. The uptake in the tumor sites did not differ significantly (P > 0.05), although in th ree of the four patients in whom tumor uptake could be calculated, it was h igher after administration of In-111-DOTATOG. Conclusion: The distribution and excretion pattern of In-111-DOTATOC resembles that of In-111-DTPAOC, an d the uptake in somatostatin-receptor-positive organs and most tumors is hi gher for In-111-DOTATOC. If Y-90-DOTATOC shows an uptake pattern similar tb In-111-DOTATOC, it is a promising radiopharmaceutical for peptide-receptor -mediated radiotherapy in patients with somatostatin-receptor-positive tumo rs.