The impact of injected peptide mass on small intestinal neuroendocrine tumor and normal organ somatostatin receptor expression; Measurements on 68Ga-DOTATOC-PET in a simulated therapy setting
Year: 2026
Type: preprint
Abstract: Background The impact of systemic somatostatin analogs on tumor versus normal organ somatostatin receptors (SSR) in conjunction with peptide receptor radionuclide therapy (PRRT) has long been debated. In a previous 68 Ga-DOTATOC-PET/CT study, at 7 h post intravenous (iv) injection of a preload of 400 µg octreotide, the SSR expression in small intestinal neuroendocrine tumors was restored to baseline levels, but remained reduced by approximately 50% in liver, spleen and pancreas creating a “therapeutic window”. The present study explored this “window” in a simulated PRRT setting in patients with disseminated Si-NETs, by firstly administer the 400 µg iv octreotide preload, and secondly 150 µg of iv octreotide at 68 Ga-DOTATOC-PET/CT, to identify possible organ protection and tumor response difference in all, large and small tumors. Methods Nine patients underwent three serial 68 Ga-DOTATOC-PET/CT examinations during two days, including both dynamic and static whole-body (WB) registrations. Each PET/CT session started with iv injection of 153 ± 30 MBq, 22.1 ± 6.7 µg (mean ± SD) 68 Ga-DOTATOC. Ten minutes before the last two PET/CT sessions, an extra iv infusion of 150 µg octreotide was administered, and five hours prior to the last PET/CT, an iv infusion of 400 µg octreotide was given. Measurements were performed of tumor uptake (mean SUV) and net influx rate (K i ), as well as SUV (mean) in abdominal organs blood and bone marrow (BM), utilized 50% iso-contour volumes of interest. Results Over time, SUV and K i in Si-NETs declined in parallel with rising peptide concentrations (p < 0.05) for the groups of all- and small tumors while the large tumor group showed no decline. A decline in SUV (30–50%) was observed in the abdominal organs at the second PET/CT scan (WB 2) (p < 0.004), performed in conjunction with 150 µg of iv octreotide, and the uptake in spleen and liver decreased further at the third PET/CT scan (WB 3) (p < 0.05). Conclusion In the presence of peptide amounts similar to those administered at PRRT, Si-NET uptake might be reduced more in small than in large tumors cancelling the potential therapeutic benefits of a 400 µg iv octreotide preload. Trial registration Regional Ethics Comitté, Uppsala, Sweden, No. 2014/39. Registered 4 June 2018, https//etikprovningsmyndigheten.se/
Source: Research Square
Institution: Uppsala University
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7225263016