Intraindividual comparison of ¹⁸ F-FDOPA and ⁶⁸ Ga-DOTATOC PET/CT detection rate for metastatic assessment in patients with ileal neuroendocrine tumours

Introduction: In patients with ileal neuroendocrine tumours (ileal NETs), head-to-head evaluation of diagnostic performances of ⁶⁸ Ga-DOTA-peptides and ¹⁸ F-fluorodihydroxyphenylalanine (¹⁸ F-FDOPA) positron emission tomography/computed tomography (PET/CT) has been performed in only few small patients' cohorts. The aim of this retrospective study was to compare ⁶⁸ Ga-DOTATOC and ¹⁸ F-FDOPA PET/CT for metastatic disease assessment in a homogeneous large series of patients with well-differentiated ileal NETs.

Methods: All patients with ileal NETs who underwent both ¹⁸ F-FDOPA and ⁶⁸ Ga-DOTATOC PET/CT within a 3-month period and no therapeutic change between the two studies were retrospectively included. The detection rates of both modalities were calculated using per-patient, per-region and per-lesion analyses.

Results: Forty one patients with ileal NETs were evaluated. ¹⁸ F-FDOPA and ⁶⁸ Ga-DOTATOC showed similar detection rates according to per-patient (97% for both) and per-region analyses (94% for ¹⁸ F-FDOPA vs 88% for ⁶⁸ Ga-DOTATOC, P = .35). For a total of 605 positive lesions, 458 (76%) were detected by both modalities, 122 (20%) exclusively by ¹⁸ F-FDOPA PET/CT, and 25 (4%) by ⁶⁸ Ga-DOTATOC PET/CT only. In a per-lesion analysis, ¹⁸ F-FDOPA PET/CT performed better than ⁶⁸ Ga-DOTATOC PET/CT (overall detection rates of 96% vs 80%; P < .001). ¹⁸ F-FDOPA PET/CT detected significantly more metastases than ⁶⁸ Ga-DOTATOC PET/CT in the liver, peritoneum, abdominal and supra-diaphragmatic lymph nodes.

Conclusion: ¹⁸ F-FDOPA PET/CT seems not inferior than ⁶⁸ Ga-DOTATOC PET/CT for the delineation of metastatic spread of ileal NETs. Therefore, according to local expertise and technical availability, ¹⁸ F-FDOPA should be considered as a valid clinical diagnostic option for exhaustive metastatic assessment in patients with ileal NETs. Obviously, ⁶⁸ Ga-DOTATOC PET/CT remains mandatory for PRRT assessment. Further comparative studies are needed to determine the optimal approach in various clinical scenarios such as preoperative staging and primary tumour detection.