PET in the diagnosis of neuroendocrine tumors.
For general oncological imaging, positron emission tomography (PET) using [18F]fluoro-deoxy-glucose (FDG) has evolved as a powerful functional imaging modality. Unfortunately, FDG-PET has not been as advantageous for imaging gastropancreatic neuroendocrine tumors, and only tumors with high proliferative activity and low differentiation have shown an increased FDG uptake. Therefore, the 11C-labeled amine precursors L-dihydroxyphenylalanine and 5-hydroxy-L-tryptophan (5-HTP) were developed for PET imaging of these tumors. Because of the higher tumor uptake of the latter tracer in a study of patients with endocrine pancreatic tumors, 11C-5-HTP was chosen for further evaluation. In comparative studies of patients with carcinoids and endocrine pancreatic tumors, 5-HTP-PET proved better than CT and somatostatin receptor scintigraphy for tumor visualization, and many small, previously overlooked lesions were diagnosed by 11C-5-HTP-PET. The strong correlation found during medical treatment between the changes in the transport rate constant at repeated PET and those of U-HIAA indicates the possible use of 11C-5-HTP-PET also for therapy monitoring. By premedication of patients with Carbidopa orally before PET examination, in order to block the aromatic amino acid decarboxylase enzyme, the decarboxylation rate of 11C-5-HTP was decreased, leading to a higher tumor uptake and a considerably lower urinary radioactivity concentration.
Sundin
Anders
A
Department of Radiology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden. anders.sundin@radiol.uu.se
Eriksson
Barbro
B
Bergström
Mats
M
Långström
Bengt
B
Oberg
Kjell
K
Orlefors
Håkan
H
D002276:Carcinoid Tumor / Q000000981:diagnostic imaging*; D006801:Humans; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging*; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging*; D014055:Tomography, Emission-Computed / Q000379:methods*