Purpose
The aim of this study was to evaluate the impact of 68Ga-labelled DOTA0-lanreotide (68Ga-DOTA-LAN) on the diagnostic assessment of neuroendocrine tumour (NET) patients with low to moderate uptake on planar somatostatin receptor (SSTR) scintigraphy or 68Ga-labelled DOTA0,Tyr3-octreotide (68Ga-DOTA-TOC) positron emission tomography (PET).
Methods
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 68Ga-DOTA-TOC PET (n = 38) due to lack of tracer uptake, underwent 68Ga-DOTA-LAN PET to evaluate a treatment option with 90Y-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.
Results
68Ga-DOTA-LAN and 68Ga-DOTA-TOC both showed equivalent findings in 24/38 patients when fused PET/CT images were interpreted. The sensitivity, specificity and accuracy of 68Ga-DOTA-LAN in comparison to CT were 0.63, 0.5 and 0.62 (n = 53; p < 0.0001) and for 68Ga-DOTA-TOC in comparison to CT 0.78, 0.5 and 0.76 (n = 38; p < 0.013), respectively. 68Ga-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 68Ga-DOTA-LAN. Corresponding values of both PET scans for tumour and liver did not show any significant correlation. 68Ga-DOTA-TOC revealed more tumour sites than 68Ga-DOTA-LAN (106 vs 53). The tumour to background ratios for tumour and liver calculated from SUVmax measurements were significantly higher for 68Ga-DOTA-TOC than 68Ga-DOTA-LAN (p < 0.02).
Conclusion
68Ga-DOTA-TOC PET imaging is an established imaging procedure for accurate staging of NET patients. 68Ga-DOTA-LAN should only be considered as a PET tracer of second choice in patients with no pathologic tracer uptake on 68Ga-DOTA-TOC PET. In these patients, 68Ga-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.