A novel read methodology to evaluate the optimal dose of (68)Ga-satoreotide trizoxetan as a PET imaging agent in patients with gastroenteropancreatic neuroendocrine tumours: a phase II clinical trial

BACKGROUND: (68)Ga-satoreotide trizoxetan is a novel somatostatin receptor antagonist exhibiting higher tumour-to-background ratios and sensitivity compared to (68)Ga-DOTATOC. This randomised, 2 × 3 factorial, phase II study aimed to confirm the optimal peptide mass and radioactivity ranges for (68)Ga-satoreotide trizoxetan, using binary visual reading. To that end, 24 patients with metastatic gastroenteropancreatic neuroendocrine tumours received 5–20 µg of (68)Ga-satoreotide trizoxetan on day 1 of the study and 30–45 µg on day 16–22, with one of three gallium-68 radioactivity ranges (40–80, 100–140, or 160–200 MBq) per visit. Two (68)Ga-satoreotide trizoxetan PET/CT scans were acquired from each patient post-injection, and were scored by experienced independent blinded readers using a binary system (0 for non-optimal image quality and 1 for optimal image quality). For each patient pair of (68)Ga-satoreotide trizoxetan scans, one or both images could score 1. RESULTS: Total image quality score for (68)Ga-satoreotide trizoxetan PET scans was lower in the 40–80 MBq radioactivity range (56.3%) compared to 100–140 MBq (90.6%) and 160–200 MBq (81.3%). Both qualitative and semi-quantitative analysis showed that peptide mass (5–20 or 30–45 µg) did not influence (68)Ga-satoreotide trizoxetan imaging. There was only one reading where readers diverged on scoring; one reader preferred one image because of higher lesion conspicuity, and the other reader preferred the alternative image because of the ability to identify more lesions. CONCLUSIONS: Binary visual reading, which was associated with a low inter-reader variability, has further supported that the optimal administered radioactivity of (68)Ga-satoreotide trizoxetan was 100–200 MBq with a peptide mass up to 50 µg. Trial registration ClinicalTrials.gov, NCT03220217. Registered 18 July 2017, https://clinicaltrials.gov/ct2/show/NCT03220217