A physiological increase in the uptake of [ ⁶⁸ Ga]Ga-labeled somatostatin analogues ([ ⁶⁸ Ga]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 [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]Ga-DOTATATE PET/CT and 113 [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]Ga-DOTATATE and 19.8 ± 9.8 g/ml for [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]Ga-DOTATOC in male patients (p = 0.02) and significant associations between UP uptake on [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]Ga-SST PET/CT with an even higher uptake in patients that had [ ⁶⁸ Ga]Ga-DOTATOC PET/CT. SUV _mean/max were significantly higher in abnormal UP uptake but there were overlaps with UP SUV values for both [ ⁶⁸ Ga]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 [ ⁶⁸ Ga]Ga-DOTATOC patients suggesting that both physiological and pathological parameters could affect UP uptake.