Functional Imaging of Neuroendocrine Tumors: A Head-to-Head Comparison of Somatostatin Receptor Scintigraphy, 123I-MIBG Scintigraphy, and 18F-FDG PET

Functional techniques are playing a pivotal role in the imaging of cancer today. Our aim was to compare, on a head-to-head basis, 3 functional imaging techniques in patients with histologically verified neuroendocrine tumors: somatostatin receptor scintigraphy (SRS) with In-111-diethylenetriaminepentaacetic acid-octreotide, scintigraphy with I-123-metaiodobenzylguanidine (MIBG), and F-18-FDG PET. Methods: Ninety-six prospectively enrolled patients with neuroendocrine tumors underwent SRS, I-123-MIBG scintigraphy, and F-18-FDG PET on average within 40 d. The functional images were fused with low-dose CT scans for anatomic localization, and the imaging results were compared with the proliferation index as determined by Ki67. Results: The overall sensitivity of SRS, I-123-MIBG scintigraphy, and F-18-FDG PET was 89%, 52%, and 58%, respectively. Of the 11 SRS-negative patients, 7 were F-18-FDG PET-positive, of which 3 were also I-123-MIBG scintigraphy-positive, giving a combined overall sensitivity of 96%. SRS also exceeded I-123-MIBG scintigraphy and F-18-FDG PET based on the number of lesions detected (393, 185, and 225, respectively) and tumor subtypes. I-123-MIBG scintigraphy was superior to F-18-FDG PET for ileal neuroendocrine tumors, and F-18-FDG PET was superior to I-123-MIBG scintigraphy for pancreaticoduodenal neuroendocrine tumors. The sensitivity of F-18-FDG PET (92%) exceeded that of both SRS (69%) and I-123-MIBG scintigraphy (46%) for tumors with a proliferation index above 15%. Conclusion: The overall sensitivity of I-123-MIBG scintigraphy and F-18-FDG PET was low compared with SRS. However, for tumors with a high proliferation rate, F-18-FDG PET had the highest sensitivity. The results indicate that, although SRS should still be the routine method, F-18-FDG PET provides complementary diagnostic information and is of value for neuroendocrine tumor patients with negative SRS findings or a high proliferation index.