Abstract
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Objectives To determine the value of 68Ga-DOTA-TOC and 18F-FDG-PET/CT for initial and follow-up evaluation of NET patients treated with peptide receptor radionuclide therapy (PRRT).
Methods We evaluated 66 patients who had histologically proven NET and underwent both PRRT and 3 combined 68Ga-DOTA-TOC and 18F-FDG-PET/CT studies. 68Ga-DOTA-TOC-PET/CT was performed before PRRT, 3 months after completion of PRRT and 6-9 months thereafter. 18F-FDG-PET/CT was done within 2 months of 68Ga-DOTA-TOC-PET/CT. Follow-up ranged 11.8-80.0 (mean:34.5) months.
Results All patients were 68Ga-DOTA-TOC-PET-positive initially and at follow-up after first full PRRT. Overall, 62/198 (31%) 18F-FDG-PET were true-positive in 38/66 (58%) patients. 28 patients (G1,5; G2,23 patients) were 18F-FDG-negative initially and during follow-up (group 1), 24 patients (G1,5; G2,13; G3,6 patients) were 18F-FDG-positive initially and during follow-up (group 2), 9 patients (G1,2; G2,6; G3,1 patient) were initially 18F-FDG-negative, but converted to 18F-FDG-positive during follow-up (group 3), and 5 patients (all G2) were initially 18F-FDG-positive, but converted to 18F-FDG-negative during follow-up (group 4).18F-FDG-PET showed more and/or larger metastases than 68Ga-DOTA-TOC-PET in 5 patients of group 2 and 4 patients of group 3, all with progressive disease. In 3 patients (progressive disease, died during follow-up) SUVmax of tumors increased 41-82% from first to last follow-up investigation.
Conclusions In NET patients, the presence of 18F-FDG-positive tumors correlates strongly with a higher risk of progression. Initially 18F-FDG-negative NET patients may show 18F-FDG-positive tumors during follow-up. Also G1 and G2 NET patients may have 18F-FDG-positive tumors. Therefore, 18F-FDG-PET/CT is a complementary tool to 68Ga-DOTA-TOC-PET/CT with clinical relevance for the molecular investigation.
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