Comparative somatostatin receptor scintigraphy using In-111-DOTA-lanreotide and In-111-DOTA-Tyr3-octreotide versus F-18-FDG-PET for evaluation of somatostatin receptor-mediated radionuclide therapy

Background: Based on the high number of somatostatin (SST) receptors expressed by neuroendocrine tumors, long-acting SST analogs have been successfully used for tumor detection. New developments point to the potential use of these types of radioligands for tumor-specific radionuclide therapy. Patients and methods: We have comparatively investigated the diagnostic capacity of the SST analog, In-111-DOTA-lanreotide (LAN), as opposed to In-111-DOTA-DPhe(1)-Tyr(3)-octreotide (TOCT) in tumor patients. This article gives an overview of recent scintigraphic results compared to CT/MRI, F-18-FDG-PET, endoscopy and/or surgery in a threshold of 218 tumor patients. Results: As opposed to radiology, previously unknown tumor lesions were demonstrable by either SST radioligand in about one third of patients. In carcinoid patients, the SST scan sensitivity was 64% for LAN (18 of 28) and 87% (34 of 39) for TOCT, whereas the sensitivity was 100% in patients with (radioiodine-negative) thyroid cancer (17 of 17) for LAN and 95% for TOCT (20 of 21). Discordant scintigraphic results between LAN and TOCT (higher tumor uptake and/or visualisation of different lesions in the same patient) were also seen in patients with lymphoma, lung cancer and intestinal adenocarcinoma. In a direct comparison of both SST tracers in 38 tumor patients, LAN gave positive results in 35 of 38, TOCT in 36 of 38 and 18F-FDG-PET in 14 of 22 of the same patients. SST scan results obtained by both tracers were equivocal in 23 of 38 patients, but were better in 10 patients with TOCT and in 5 patients with LAN. Conclusions: We conclude that both SST radioligands are suitable tracers for tumor imaging, but may give significantly different uptake results for different tumor types. Since the uptake is most important for tumor therapy, using either long-acting SST analogs, and/or Y-90-labeled analogs, careful evaluation should be made prior to therapy.