Correlation analysis of serum glucose level with physiologic ⁶⁸Ga-DOTA-TOC by the pancreas uncinated process.

Introduction: ⁶⁸Ga-DOTA-TOC PET has been widely used for the diagnosis and staging of somatostatin receptor (SSTR) expressing tumors. Image interpretation of ⁶⁸Ga-DOTA-TOC PET in pancreatic neuroendocrine tumors is cautious because physiologic expression of SSTR in the pancreas uncinate process is often misinterpreted as SSTR-expressing tumor. As physiologic DOTA-TOC uptake of pancreas head reflects expression and metabolic activity of Pancreatic polypeptide (PP) cells in pancreas, we investigated the association of serum glucose level with DOTA-TOC uptake of PP cell-rich lesion in pancreas head.

Methods: Twenty-nine patients (male : female= 12 : 17, age = 51.24 ± 16.70y [mean±SD]), who underwent ⁶⁸Ga-DOTA-TOC PET scans were retrospectively enrolled. Patients diagnosed with diabetes mellitus and patients with serum glucose over 200mg/dL were excluded. Before the PET scan, the fasting serum glucose level was examined right before ⁶⁸Ga-DOTA-TOC injection. ⁶⁸Ga-DOTA-TOC uptake was measured by the maximum standardized uptake values (SUVmax). In addition, PP-cell volume (PPvol) was assessed by areas with ⁶⁸Ga-DOTA-TOC uptake using a cut-off of 40% SUVmax. Correlation of serum glucose levels and standardized uptake values (SUVmax), SUV ratio of uncinate process uptake and pancreas body uptake, and PPvol were calculated.

Results: For the comparison of ⁶⁸Ga-DOTA-TOC PET parameters of uncinate process uptake from 29 patients, the mean value of SUVmax was 6.637±1.546 [mean±SD], PPvol was 9.192 cm³ ±5.238 [mean±SD], and SUV ratio of uncinate process uptake and normal pancreas uptake was 2.946 ±0.526 [mean±SD]. A significant negative correlation was found between SUVmax of the pancreas uncinated process and serum glucose level (r = -0.49, p = 0.007). In addition, PPvol was also significantly negatively correlated with the serum glucose level (r = -0.48, p = 0.09). SUVratio of pancreas uncinate process to pancreas body showed a trend of negative correlation with serum glucose with a borderline significance (r = -0.35, p = 0.06).

Conclusions: Physiologic DOTA-TOC uptake of pancreas uncinate process is negatively correlated with serum glucose level. Our results suggested that hypoglycemic condition could stimulate PP-cells in pancreas uncinate that eventually affected ⁶⁸Ga-DOTA-TOC PET interpretation for pancreas NET.