Detection of pancreatic neuroendocrine tumors (PNET) using semi-quantitative [68Ga]DOTATOC PET in combination with multiphase contrast-enhanced CT.

Aim: Pancreatic neuroendocrine tumors (PNETs) pose a diagnostic challenge with respect to the physiologic somatostatin receptor expression in the uncinate process representing a potential pitfall for receptor imaging with PET/CT. Methods: We identified 49 PNETs from a total of 316 consecutive [68Ga]DOTATOC PET/CT examinations for whom the detections rates of PET and multiphase contrast enhanced (CE-) CT could be retrospectively compared and 38 PNETs for which SUV max and SUV max target-to-liver ratios could be calculated for the tumors and the uncinate process. Results: The detection rate of PET (83.7%) was higher than of the different CT phases (arterial: 59.2%, P=0.017; portal-venous: 38.8%, P<0.001; venous: 46.9%, P=0.001; multiphase: 71.4%, P=0.286). Compared to the other method PET revealed 28.6% additional lesions and multiphase CE-CT 16.3%. The portal-venous phase revealed only lesions that were also detected in the arterial or venous phase. The detection rate for PNETs in the uncinate process (N.=9) was 66.7% for PET versus 55.6% for multiphase CE-CT. SUV max and SUV max target-to-liver ratios differed significantly (P<0.001) for PNETs (mean, range: SUV max,14.6, 1.4-69.3; SUV max target-to-liver ratio, 3.2, 0.69-23.1) and uncinate process (4.32, 0.8-13.5; 0.94, 0.51-1.56), however with a wide overlap. Conclusion: Patients with PNETs should undergo [68Ga]DOTATOC PET/CT with at least an arterial and venous phase CT scan. SUV max and SUV max target-to-liver ratios provide additional information but do no reliably separate PNETs from normal tracer uptake in the uncinate process.