Uptake of 68Ga-DOTATATE and 68Ga-DOTATOC in Primary Neuroendocrine Tumors, Metastases, and Normal Liver Tissue: Is There a Significant Difference?

Abstract

Purpose: Intrapatient comparison of in vivo distribution of two Ga-68-labeled somatostatin (agonist) analogues with different in vitro affinities for human somatostatin receptor (sstr) subtypes 2, 3, and 5 by determining their SUVmax values in normal liver, primary tumors, and metastases in gastroenteropancreatic (GEP) neuroendocrine tumor (NET) patients. Methods: 68Ga-DOTATATE and 68Ga-DOTATOC PET/CT studies were performed at consecutive visits in 38 GEP NET patients (1 duodenal, 18 pancreatic, 2 cecal, 12 ileal, 3 jejunal, 1 mesenteric, 1 NET in appendix) with stable disease on both occasions, with 197 days (117-311 days range) in between. Time to start of scanning after injection was identical for both studies. SUVmax for both radiopharmaceuticals in primary tumors, liver-, lymph node-, soft tissue-, and bone-metastases and in normal liver tissue were compared. Results: Overall, 225 metastases (98 liver, 67 lymph node, 43 bone, 17 soft tissue) and 18 primary GEP NETs were analyzed on both 68Ga-DOTATOC and 68Ga-DOTATATE studies. Mean SUVmax in the TATE/TOC groups were: normal liver 6.8 ± 1.7/6.9 ± 1.8, metastases in the liver 15.4 ± 9.4/17.9 ± 11.4, lymph nodes12.0 ± 9.5/15.2 ± 13.3, bones 7.5 ± 5.7/9.9 ± 8.0, soft tissues 15.3 ± 16.4/17.3 ± 18.8, primary tumor 20.4 ± 13.7/24.23 ± 20.1. Average 68Ga-DOTATOC accumulation was always higher. The differences between TATE/TOC groups were significant in primary tumors, liver-, lymph node-, and bone-metastases, but not in soft tissue-metastases. Notwithstanding these highly significant differences, considerable variability amongst patients in preferred tracer uptake was observed. Conclusions: On average, 68Ga-DOTATOC shows significantly higher uptake in GEP NET primary tumors and metastases than 68Ga-DOTATATE. However, we have also observed considerable variability in preferred peptide uptake. Optimal therapy planning would therefore require somatostatin receptor imaging with both these peptides. © The Editor(s) (if applicable) and The Author(s) 2024.