Intrapatient ⁶⁸Ga-DOTATOC/⁶⁸Ga-DOTATATE uptake comparison in primary neuroendocrine tumors, metastases and normal liver.

Objectives Two ⁶⁸Ga-labeled somatostatin analogues [TOC&TATE; TOC exhibiting higher affinity for human somatostatin receptor 3&5, lower for 2] in vivo distribution comparison by determining standardized uptake values (SUVmax) in normal liver, primary gastroenteropancreatic neuroendocrine tumor (NET) and metastases (mets).

Methods 76 PET/CT studies in 38 patients (1 duodenal NET, 18 pancreatic, 2 coecal, 12 ileal, 3 jejunal, 1 mesenterial, 1 in appendix) with stable disease were analyzed. ⁶⁸Ga-DOTATATE and ⁶⁸Ga-DOTATOC PET/CT were performed at consecutive controls. Mean SUVmax values were determined and compared.

Results 225 metastases (98 liver, 67 lymph node, 43 bone, 17 soft tissue), 18 primaries and normal liver were analyzed on both PET/CTstudies. Mean SUVmax values in TATE/TOC group were: normal liver 6.8±1.7/6.9±1.8, primary tumor 20.4±13.7/24.2±20.1, liver mets 15.4±9.4/17.9±11.4, soft tissue mets 15.3±16.4/17.3±18.8, lymph node mets 12.0±9.5/15.2±13.3, bone mets 7.5±5.7/9.9±8.0. TOC uptake was always higher: highly significantly in primaries, liver and lymph node mets, significantly in bone mets, not significantly in soft tissue mets. TOC&TATE accumulated higher in primaries compared to mets. The highest metastatic uptake was in liver and soft tissue mets (not significantly different compared to primaries), intermediate in lymph nodes (significantly lower than in primaries) and the lowest in bone mets. Normal liver tissue showed the lowest uptake.

Conclusions ⁶⁸Ga-DOTATOC had higher uptake (that could be beneficial in theranostic approach) in primaries and mets. The highest binding (3.5 fold higher than in normal liver) was in primaries. Liver and soft tissue mets had the highest, lymph node intermediate, bone the lowest metastatic uptake. Normal liver showed no difference in TOC/TATE accumulation.