Dynamic ⁶⁸Ga-DOTA⁰-Tyr³-octreotate positron emission tomography-computed tomography for the evaluation of pancreatic neuroendocrine tumors: a pilot study

Background: Ga-68-DOTA(0)-Tyr3-octreotate (Ga-68-DOTATATE) is a radiolabeled somatostatin analog used for the diagnosis of pancreatic neuroendocrine tumors (pNETs), and standardized uptake value (SUV) measurements for therapeutic monitoring is recommended. However, changes in net influx rate (K-i) may better reflect treatment effects than may those of the SUV. The aim of this study was to investigate the value of dynamic Ga-68-DOTATATE positron emission tomography-computed tomography (PET-CT) in the evaluation of pNETs. Methods: Dynamic PET-CT scans over 60 min were acquired for 7 patients with localized pancreatic mass before surgery. Maximal and mean SUV (SUVmax and SUVmean) were measured in tumors and normal pancreatic body as reference tissue (RT). Time-activity curves (TACs) were extracted from tumors and RT. A 2-tissue compartment model was used to calculate the rate constants K-1, k(2), and k(3) (min(-1)); K-i (mL/g/min); and K-1:k(2) ratio. The following statistical tests were used to evaluate the results: the Shapiro-Wilk, Student t test, Mann-Whitney, Spearman, and Pearson rank correlation tests. Results: Among 6 patients, 8 primary tumors were histopathologically proven to be pNETs. Moreover, 6 lesions with high uptake of Ga-68-DOTATATE showed an ascending TAC pattern, while 2 lesions with no or low uptake showed a descending TAC pattern. The mean SUVmax and SUVmean of pNETs were 46.4 +/- 40.2 (range, 3.9-109.9) and 21.9 +/- 16.0 (range, 0.5-42.8), respectively, which were significantly higher than the SUVmax of 4.2 +/- 0.6 (range, 3.1-4.9) and the SUVmean of 2.7 +/- 1.0 (range, 1.4-3.6) for the RT (P=0.021 and P=0.036), respectively. The K-i of pNETs was statistically higher than that of the RT [pNET: 0.366 +/- 0.372 (range, 0.019-0.992); RT: 0.060 +/- 0.017 (range, 0.04-0.08); P=0.036]. The mean K-1:k(2) ratio in pNETs was 12fold higher than that of RT (6.06 vs. 0.50). In pNETs, there was a positive correlation between SUVmax and K-i (r=0.952; P<0.001) and between SUVmean and K-i (r=0.905; P=0.002). Another patient was diagnosed with intrapancreatic accessory spleen. Conclusions: The uptake of Ga-68-DOTATATE by pNETs can be explained by its high K-i value and K1:k2 ratio. Dynamic Ga-68-DOTATATE PET-CT can serve as a potential tool for evaluating pNETs and support the further assessment of a larger cohort of patients.