Imaging of advanced neuroendocrine tumors with (18)F-FDOPA PET

Nuclear medicine plays an important role in the imaging of neuroendocrine tumors (NETs). Somatostatin receptor scintigraphy (SRS) with (111)In-labeled somatostatin receptor analogs is a standard procedure for the detection and staging of NET. Based on the ability of NETs to store biogenic amines, this study evaluated whether 6-(18)F-fluoro-L-DOPA ((18)F-FDOPA) is a suitable PET tracer for NETs.

Twenty-three patients with histologically verified NETs in advanced stages were consecutively enrolled in the study. All patients underwent PET with (18)F-FDOPA, CT, and SRS within 6 wk. In patients with discrepancies between nuclear medicine and radiologic methods, follow-up investigations were performed by CT, MRI, and ultrasound. (18)F-FDOPA PET with attenuation correction was done 30 and 90 min after injection from the neck to the upper legs. SRS was performed with (111)In-DOTA-D-Phe(1)-Tyr(3)-octreotide at 6 and 24 h. All images were read without knowledge of the results of the other modalities. In every patient, the following regions were evaluated separately: bones, mediastinum, lungs, liver, pancreas, and others, including the abdominal and supraclavicular lymph nodes, spleen, and soft- tissue lesions. The findings were confirmed by clinical examination. The nuclear medicine methods were compared against morphologic imaging, which was considered as gold standard.

The most frequently involved organs or regions were the liver (prevalence, 70%) and bone (52%), followed by mediastinal foci (31%), the lungs (22%), and the pancreas (13%). Fifty-two percent of patients had various lymphatic lesions. (18)F-FDOPA was most accurate in detecting skeletal lesions (sensitivity, 100%; specificity, 91%) but was insufficient in the lung (sensitivity, 20%; specificity, 94%); SRS yielded its best results in the liver (sensitivity, 75%; specificity, 100%); however, it was less accurate than PET in all organs. In about 40%, initial CT failed to detect bone metastases shown by PET that were later on verified by radiologic follow-up.

(18)F-FDOPA PET performs better than SRS in visualizing NETs and may even do better than CT for bone lesions. SRS is essential to establish the usefulness of therapy with somatostatin analogs, yet is less accurate than (18)F-FDOPA PET for staging.