Dual-tracer (18F-FDG and 18F-DOPA) PET/CT in evaluation of neuroendocrine tumors: An Asian study

Objectives Neuroendocrine tumors (NETs) are rare malignancies originating from neural crest cells throughout the body. 18F-FDG PET/CT is known to have limited role in NET detection. Data of 18F-DOPA PET/CT on NET have been mostly reported by the Western countries. We aimed to evaluate the incremental value of dual-tracer (18F-FDG and 18F-DOPA) PET/CT to 18F-DOPA alone in the assessment of NET in Asian patients.

Methods Patients with known or suspected NETs referred for PET/CT during year 2007~10 were retrospectively reviewed and those with histopathological confirmation before or after PET/CT within 2 months or with uneventful findings upon serial PET/CT within 6 months were recruited into this study. All patients underwent two-day protocol of 18F-FDG and 18F-DOPA PET/CT within 1 week. Pre-medication with Carbidopa (200 mg) was given orally 60 minutes before 18F-DOPA injection. Whole-body PET/CT was performed 60 minutes after tracer injection and PET/CT images were reviewed by 3 nuclear medicine physicians in consensus.

Results 26 patients (M: 16, F: 10, mean age: 53±18.3 years) with/without treatment (untreated: 12, treated: 14) before PET/CT were evaluated. Histopathological results confirmed NETs in 23 patients with primary sites at adrenal gland (N=4), rectum (3), colon (2), stomach (1), pancreas (4), appendix (1), urinary bladder (1), thyroid (1), neck (1) and unknown primary with hepatic NET metastases (5). 18F-DOPA PET/CT was true positive in 16/23 and false negative (FN) in 7/23. Of the 7 FN patients, 18F-FDG PET/CT was able to detect 4/7: pancreas (2), rectum (1) and liver (1). Therefore the sensitivity of 18F-DOPA alone versus dual-tracer PET/CT was 70% (16/23) versus 87% (20/23), respectively. The remaining 3 FN patients all had very small colonic carcinoid lesions (2mm, 3mm and 6mm). For the 3 negative patients confirmed by serial PET/CT, both 18F-DOPA and 18F-FDG PET/CT showed true negative findings (specificity: 100%).

Conclusions Dual-tracer PET/CT has an incremental value to 18F-DOPA alone in increasing the detection sensitivity for NET patients