Somatostatin receptor PET in neuroendocrine tumours: 68Ga-DOTA0,Tyr3-octreotide versus 68Ga-DOTA0-lanreotide

The aim of this study was to evaluate the impact of Ga-68-labelled DOTA(0)-lanreotide (Ga-68-DOTA-LAN) on the diagnostic assessment of neuroendocrine tumour (NET) patients with low to moderate uptake on planar somatostatin receptor (SSTR) scintigraphy or Ga-68-labelled DOTA(0),Tyr(3)-octreotide (Ga-68-DOTA-TOC) positron emission tomography (PET). Fifty-three patients with histologically confirmed NET and clinical signs of progressive disease, who had not qualified for peptide receptor radionuclide therapy (PRRT) on planar SSTR scintigraphy or Ga-68-DOTA-TOC PET (n = 38) due to lack of tracer uptake, underwent Ga-68-DOTA-LAN PET to evaluate a treatment option with Y-90-labelled lanreotide according to the MAURITIUS trial. The included patients received 150 +/- 30 MBq of each radiopharmaceutical intravenously. PET scans were acquired 60-90 min after intravenous bolus injection. Image results from both PET scans were compared head to head, focusing on the intensity of tracer uptake in terms of treatment decision. CT was used for morphologic correlation of tumour lesions. To further evaluate the binding affinities of each tracer, quantitative and qualitative values were calculated for target lesions. Ga-68-DOTA-LAN and Ga-68-DOTA-TOC both showed equivalent findings in 24/38 patients when fused PET/CT images were interpreted. The sensitivity, specificity and accuracy of Ga-68-DOTA-LAN in comparison to CT were 0.63, 0.5 and 0.62 (n = 53; p < 0.0001) and for Ga-68-DOTA-TOC in comparison to CT 0.78, 0.5 and 0.76 (n = 38; p < 0.013), respectively. Ga-68-DOTA-TOC showed a significantly higher maximum standardized uptake value (SUVmax) regarding the primary tumour in 25 patients (p < 0.003) and regarding the liver in 30 patients (p < 0.009) compared to Ga-68-DOTA-LAN. Corresponding values of both PET scans for tumour and liver did not show any significant correlation. Ga-68-DOTA-TOC revealed more tumour sites than Ga-68-DOTA-LAN (106 vs 53). The tumour to background ratios for tumour and liver calculated from SUVmax measurements were significantly higher for Ga-68-DOTA-TOC than Ga-68-DOTA-LAN (p < 0.02). Ga-68-DOTA-TOC PET imaging is an established imaging procedure for accurate staging of NET patients. Ga-68-DOTA-LAN should only be considered as a PET tracer of second choice in patients with no pathologic tracer uptake on Ga-68-DOTA-TOC PET. In these patients, Ga-68-DOTA-LAN PET can provide valuable information when evaluating PRRT as the treatment option, as a broader spectrum of human SSTR subtypes can be detected.