Impact of peptide receptor radionuclide therapy on the 68Ga-DOTATOC-PET/CT uptake in normal tissue.

Positron-emission tomography/computed tomography (PET/CT) with [68Ga]DOTA0-Phe1-Tyr3-octreotide (68Ga-DOTA-TOC) became a standard for somatostatin receptor imaging. We investigated the potential changes of normal tissue uptake in patients with neuroendocrine tumor undergoing peptide receptor radionuclide therapy (PRRT).Sixteen patients underwent [68Ga]-DOTA-TOC-PET/CT prior and after 4-6 cycles of PRRT (mean administered activity: 13.8 GBq 90Y+ 9.6 177Lu). The maximum standardized uptake values (SUVmax) of pituitary, thyroid, spleen, liver parenchyma, pancreas, kidneys and adrenals were determined, respectively.SUVmax values prior and after PRRT were in pituitary (5, 56±2,91/ 4,47±2,53), thyroid (2.05±1.11/ 2.49±2.47), spleen (24.95±14.20/20.06±8.53), liver (7.13±3.96/6.62±2.63), pancreas (6.96±1.99/6.83±2.00), kidneys (13.0±3.85/11.31±3.31) and adrenals (9.65± 4.20/7.10±2.86). A comparison of pre- and post treatment values revealed no significant differences (P>0.05) in any of these organs.The uptake of [68Ga] DOTA-TOC in normal tissue is not significantly affected by PRRT. This is relevant with regards to therapeutic monitoring were tumor-to-non-tumor ratio seems to be the most robust biomarker.