Other Radiopharmaceuticals for Imaging GEP‐NET

In GEP‐NETs, especially the catecholamine and serotonin biosynthetic pathways are upregulated. Therefore, increased biosynthesis of these specific amines in GEP‐NETs enables imaging with specific amine precursors. For the catecholamine pathway, 6‐18F ‐l‐3,4‐dihydroxyphenylalanine (18F‐DOPA) is available, while for the serotonin pathway, carbon‐11‐labeled 5‐hydroxy‐l‐tryptophan ([11C]‐5‐HTP) is available as tracer. 11C‐5‐HTP PET and 18F‐DOPA PET are excellent functional imaging techniques for evaluating patients with proven pancreatic islet cell tumors and carcinoids. For both tracers, the combination with CT further improves the detection rate of NET, which shows that performing PET scans with these tracers in PET/CT scanners is beneficial for patients.

Since well‐differentiated GEP‐NETs generally have a low glucose metabolism, 18F‐fluorodexyglucose (18F‐FDG) PET scanning has limited value for the primary staging of patients with well‐differentiated GEP‐NETs. However, in patients with rapidly progressive disease, dedifferentiation of GEP‐NET tumors can lead to a higher glucose metabolism in tumor cells. In these patients, 18F‐FDG PET can be of benefit for tumor staging. Also, 18F‐FDG PET can be of value when other malignancies are suspected in patients with GEP‐NETs, since these patients experience a higher incidence of these malignancies compared to the general population.

Nowadays, (GEP)‐NETs can also be imaged with 68Ga‐labeled analogues of somatostatin, which are also PET tracers. Advantages of 68Ga‐labeled somatostatin analogues are the relatively easy generator‐based synthesis and the possibility to evaluate whether peptide (somatostatin) receptor radionuclide therapy (PRRT) for NETs can be considered.