The aim of this study was to evaluate the diagnostic value of a new somatostatin analog, (68)Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotide ((68)Ga-DOTA-TOC), for PET in patients with known or suspected neuroendocrine tumors. PET was compared with conventional scintigraphy and dedicated CT.
Methods: Eighty-four patients (48 men, 36 women; age range, 28-79 y; mean age +/- SD, 58.2 +/- 12.2 y) were prospectively studied. For analysis, patients were divided into 3 groups: detection of unknown primary tumor in the presence of clinical or biochemical suspicion of neuroendocrine malignancy (n = 13 patients), initial tumor staging (n = 36 patients), and follow-up after therapy (n = 35 patients). Each patient received 100-150 MBq (68)Ga-DOTA-TOC. Imaging results of PET were compared with (99m)Tc-labeled hydrazinonicotinyl-Tyr(3)-octreotide ((99m)Tc-HYNIC-TOC) and (111)In-DOTA-TOC. CT was also performed on every patient using a multidetector scanner. Each imaging modality was interpreted separately by observers who were unaware of imaging findings before comparison with PET. The gold standard for defining true-positive (TP), true-negative (TN), false-positive (FP), and false-negative (FN) results was based on all available histologic, imaging, and follow-up findings.
Results: PET was TP in 69 patients, TN in 12 patients, FP in 1 patient, and FN in 2 patients, indicating a sensitivity of 97%, a specificity of 92%, and an accuracy of 96%. The FP finding was caused by enhanced tracer accumulation in the pancreatic head, and the FN results were obtained in patients with a tumor of the gastrointestinal tract displaying liver metastases. (68)Ga-DOTA-TOC showed higher diagnostic efficacy compared with SPECT (TP in 37 patients, TN in 12 patients, FP in 1 patient, and FN in 34 patients) and diagnostic CT (TP in 41 patients, TN in 12 patients, FP in 5 patients, and FN in 26 patients). This difference was of statistical significance (P < 0.001). However, the combined use of PET and CT showed the highest overall accuracy.
Conclusion: (68)Ga-DOTA-TOC PET shows a significantly higher detection rate compared with conventional somatostatin receptor scintigraphy and diagnostic CT with clinical impact in a considerable number of patients.