Carbidopa-assisted 18F-fluorodihydroxyphenylalanine PET/CT for the localization and staging of non-functioning neuroendocrine pancreatic tumors

CD premedication was found to increase the value of F-18-fluorodihydroxyphenylalanine (F-18-FDOPA) PET/CT imaging in the detection of adult insulinoma. The aim of this study was to evaluate the performance of CD-assisted F-18-FDOPA PET/CT in the diagnosis and staging of non-functioning pNETs. Twenty consecutive patients with low-grade pNETs who underwent CD-assisted F-18-FDOPA PET/CT imaging and In-111-somatostatin receptor scintigraphy (SRS) were evaluated. Histology was considered as the gold standard. In case where no surgical resection was performed, the diagnosis of pNET was made by the confrontation of the different available imaging modalities. CD-assisted F-18-FDOPA PET/CT was positive in 18/20 cases (90 %), whereas SRS was positive in 13/19 cases (68 %). When considered the 19 patients underwent both nuclear medicine examinations, F-18-FDOPA PET/CT was significantly more sensitive then SRS for primary tumor detection (p = 0.049). False-negative results of both F-18-FDOPA PET/CT and SRS were observed in 2 cystic pNETs. SRS failed to detect one additional cystic tumor and 3 pNETs of 10, 12 and 17 mm, respectively. F-18-FDOPA PET/CT correctly identified all patients with lymphatic, visceral and bone metastases. SRS failed to detect lymphatic spread and was falsely negative in one patient with splenic metastasis. Contrary to widely held assumptions, our study further expands the application of CD-assisted F-18-FDOPA PET/CT for non-functioning pNETs when Ga-68-radiolabeled somatostatin analogs are not available.