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

Abstract

AbstractPurpose: 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.