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

Abstract

Background 68Ga-satoreotide trizoxetan is a novel somatostatin receptor antagonist exhibiting higher tumour-to-background ratios and sensitivity compared to 68Ga-DOTATOC. This randomised, 2 × 3 factorial, phase II study aimed to confirm the optimal peptide mass and radioactivity ranges for 68Ga-satoreotide trizoxetan, using binary visual reading. To that end, 24 patients with metastatic gastroenteropancreatic neuroendocrine tumours received 5–20 µg of 68Ga-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 68Ga-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 68Ga-satoreotide trizoxetan scans, one or both images could score 1. Results Total image quality score for 68Ga-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 68Ga-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 68Ga-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