Direct comparison of 68Ga-DOTA-TOC and 18F-FDG PET/CT in the follow-up of patients with neuroendocrine tumour treated with the first full peptide receptor radionuclide therapy cycle

Abstract

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