68Ga-satoreotide trizoxetan is a novel somatostatin receptor antagonist exhibiting high tumor-to-background ratios and sensitivity. A randomized, 2 x 3 factorial, phase II study was conducted between September 2017 and August 2019 with the goal of confirming the optimal peptide mass and radioactivity ranges for 68Ga-satoreotide trizoxetan using binary visual reading. The results of the study have recently been published in EJNMMI Research.
The Bracken Group’s own Colin G. Miller is the lead author of this paper. This post aims to summarize the researchers’ key points.
Twenty-four patients with metastatic gastroenteropancreatic neuroendocrine tumors received 5–20 µg of 68Ga-satoreotide trizoxetan on day 1 of the study and 30-45 µg on day 16-22. One of three gallium-68 radioactivity ranges was used per visit—40-80, 100-140, or 160-200 MBq. 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 in which “0” indicated non-optimal image quality and “1” indicated optimal image quality. For each patient pair of 68Ga-satoreotide trizoxetan scans, one or both images could score “1”.
The total image quality score for 68Ga-satoreotide trizoxetan PET scans was lower in the 40-80 MBq radioactivity range (56.3%) compared to the 100-140 MBq and 160-200 MBq ranges (90.6% and 81.3%, respectively). Both qualitative and semi-quantitative analyses showed that peptide mass did not influence imaging.
Readers diverged on scoring only once: In this case, one reader preferred an image because of higher lesion conspicuity, while the other reader preferred the alternative image because of the ability to identify more lesions. See the full paper with complete details here.
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. In addition, the study provided the opportunity to develop a simple, precise image quality scoring system associated with low inter-reader variability. This binary scoring system can now be recommended for future evaluations of imaging studies.
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