The aim of this study was to evaluate the diagnostic value of a new somatostatin analog, ⁶⁸Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N″,N″′-tetraacetic acid-d-Phe¹-Tyr³-octreotide (⁶⁸Ga-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 ⁶⁸Ga-DOTA-TOC. Imaging results of PET were compared with ^99mTc-labeled hydrazinonicotinyl-Tyr³-octreotide (^99mTc-HYNIC-TOC) and ¹¹¹In-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. ⁶⁸Ga-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: ⁶⁸Ga-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.

Somatostatin receptor scintigraphy is an accurate imaging modality for the diagnosis of neuroendocrine tumor. Because detection of distant metastases has a major impact on treatment, early diagnosis of metastatic spread is of great importance. So far, no standard procedure has become established for the early diagnosis of bone metastases from neuroendocrine tumor. We compared the diagnostic value of CT with that of the novel somatostatin analog ⁶⁸Ga-1,4,7,10-tetraazacyclododecane-N,N′,N″,N′′′-tetraacetic acid-d-Phe¹-Tyr³-octreotide (⁶⁸Ga-DOTATOC) in the detection of such metastases. Methods: Fifty-one patients (22 women and 29 men; age range, 32–87 y) with histologically verified neuroendocrine tumor were included in this study. PET scans were fused with CT scans using a vacuum fixation device. ¹⁸F-NaF or ^99mTc-dicarboxypropane diphosphonate bone scans or clinical follow-up served as the reference standard. Results: Twelve of the 51 patients had no evidence of bone metastases on any of the available imaging modalities, and 37 patients had ⁶⁸Ga-DOTATOC PET results true-positive for bone metastases. ⁶⁸Ga-DOTATOC PET results were true-negative for 12 patients, false-positive for one, and false-negative for another, resulting in a sensitivity of 97% and a specificity of 92%. ⁶⁸Ga-DOTATOC PET detected bone metastases at a significantly higher rate than did CT (P < 0.001). Furthermore, conventional bone scans confirmed the results of somatostatin receptor PET but did not reveal additional tumors in any patients. Conclusion: ⁶⁸Ga-DOTATOC PET is a reliable, novel method for the early detection of bone metastases in patients with neuroendocrine tumor. Our results show that CT and conventional bone scintigraphy are less accurate than ⁶⁸Ga-DOTATOC PET in the primary staging or restaging of neuroendocrine tumor.