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

PurposeTo 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).MethodsWe 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).ResultsAll 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.ConclusionIn 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.

Current Concepts in 68Ga-DOTATATE Imaging of Neuroendocrine Neoplasms: Interpretation, Biodistribution, Dosimetry, and Molecular Strategies

“…The rationale for using 18 F-FDG relies on its ability to identify the presence of aggressive disease foci-an ability that may turn into a better stratification of patients at major risk of progression. The clinical scenario of double-tracer imaging findings ranges from purely SSR-positive/ 18 F-FDGnegative cases to 18 F-FDG-positive/SSRnegative cases, with a very heterogeneous intermediate group presenting various patterns of uptake in the same patient with both tracers in the same or in different lesions over time (52). The most important lesson deriving from these studies is the demonstration of the heterogeneous nature of NENs.…”

“…Vice versa, 68 Ga-SSA PET/CT in cases presenting higher Ki-67 values (.50%), even if positive, will likely not affect management. The added value of 18 F-FDG in welldifferentiated NENs (G1 and G2) is still under debate, and no international consensus has been reached (49)(50)(51)(52)(53).…”

Molecular imaging in neuroendocrine tumors: recent advances, controversies, unresolved issues, and roles in management

“…Older studies suggested that 18 F-FDG-PET/CT had minimal utility in NETs, however, more recent studies show a percentage of NETs have high 18 F-FDG-PET/CT activity[74, 77–84]. Recently there have been a number of studies attempting to define the potential usefulness of 18 F-FDG-PET/CT and 68 Ga-DOTA-peptide-PET/CT either alone or together[74, 77, 79, 80].…”

“…Older studies suggested that 18 F-FDG-PET/CT had minimal utility in NETs, however, more recent studies show a percentage of NETs have high 18 F-FDG-PET/CT activity[74, 77–84]. Recently there have been a number of studies attempting to define the potential usefulness of 18 F-FDG-PET/CT and 68 Ga-DOTA-peptide-PET/CT either alone or together[74, 77, 79, 80]. In general, these studies support the conclusion that 68 Ga-DOTA-peptide-PET/CT demonstrated superior imaging in well-differentiated G1/G2 NETs compared to 18 F-FDG-PET/CT, whereas 18 F-FDG-PET/CT demonstrates higher uptake in poorly-differentiated G3 NETs than 68 Ga-DOTA-peptide-PET/CT[77, 79].…”

“…Recently there have been a number of studies attempting to define the potential usefulness of 18 F-FDG-PET/CT and 68 Ga-DOTA-peptide-PET/CT either alone or together[74, 77, 79, 80]. In general, these studies support the conclusion that 68 Ga-DOTA-peptide-PET/CT demonstrated superior imaging in well-differentiated G1/G2 NETs compared to 18 F-FDG-PET/CT, whereas 18 F-FDG-PET/CT demonstrates higher uptake in poorly-differentiated G3 NETs than 68 Ga-DOTA-peptide-PET/CT[77, 79]. A similar pattern is seen with lung carcinoids with 68 Ga-DOTA-peptide-PET/CT being more sensitive than 18 F-FDG-PET/CT for detecting typical carcinoids, whereas the reverse was true for atypical lung carcinoids[85•].…”