Increased [⁶⁸Ga]Ga-SST uptake in the uncinate pancreatic process in new digital PET/CT machine and potential...

A physiological increase in the uptake of [⁶⁸Ga]Ga-labeled somatostatin analogues ([⁶⁸Ga]Ga-SST) PET tracers has been reported in the uncinate pancreatic process (UP) and might be even higher in latest generation of PET/CT scanners and might be falsely interpreted as NET. We aimed to investigate the uptake of UP in a large population of NET patients who underwent [⁶⁸Ga]Ga-SST PET/CT with digital SiPM detectors. We also explored potential associations between UP uptake and various clinical, imaging, and pathological factors routinely assessed in NET patients.

We analyzed all consecutive NET patients from July 2018 to June 2022 in this retrospective, single-center study. All patients underwent a [⁶⁸Ga]Ga-SST PET/CT scan on a digital SiPM PET/CT scanner. On visual analysis, we distinguished between normal linear and homogenous UP uptake or abnormal if otherwise. We compared SUV_max/mean in patients with normal UP uptake to those with abnormal UP uptake with suspicious NET lesions on contrast-enhanced CT (ce-CT) and according to the site of the primary NET (pancreatic NET vs. other), patient gender (female vs. male) and tumor grade (grade 1-2 vs. 3) using a Mann-Whitney test. We also assessed the correlation between SUV_max/mean values in UP with patients' age, primary NET Ki-67 counting, and its SUV_max/mean, TLA and MTV values.

We included 131 NET patients with a total of 34 [⁶⁸Ga]Ga-DOTATATE PET/CT and 113 [⁶⁸Ga]Ga-DOTATOC PET/CT scans. An abnormal UP uptake was seen in 32 patients with 65.7% of suspicious NET lesion or extrinsic compression on morphological imaging. Normal UP uptake SUV_max/mean were measured in 115 [⁶⁸Ga]Ga-SST scans (78.2%) with normal UP uptake and without suspicious lesion on morphological imaging. We found an average SUV_max of 12.3 ± 4.1 for [⁶⁸Ga]Ga-DOTATATE and 19.8 ± 9.8 g/ml for [⁶⁸Ga]Ga-DOTATOC, hence higher than those reported in the literature [SUVmax 5 ± 1.6 to 12.6 ± 2.2 g/ml] with significant difference with abnormal UP uptake and between both PET tracers (both p < 0.01). Significant results were a higher UP uptake on [⁶⁸Ga]Ga-DOTATOC in male patients (p = 0.02) and significant associations between UP uptake on [⁶⁸Ga]Ga-DOTATOC and SUV_max/mean of the primary tumor (ρ [0.337-0.363]; p [0.01-0.02]).

We confirmed a higher and very frequent UP uptake in latest SiPM-detector [⁶⁸Ga]Ga-SST PET/CT with an even higher uptake in patients that had [⁶⁸Ga]Ga-DOTATOC PET/CT. SUV_mean/max were significantly higher in abnormal UP uptake but there were overlaps with UP SUV values for both [⁶⁸Ga]Ga-SST and a correlation to morphological imaging is crucial. Besides, significant associations between UP uptake and SUV_mean/max of the primary NET as well as patients' gender were seen in the larger cohort of [⁶⁸Ga]Ga-DOTATOC patients suggesting that both physiological and pathological parameters could affect UP uptake.