High-yield, standardised automated radiosynthesis process for routine clinical insulinoma PET with [⁶⁸Ga]Ga-NODAGA-exendin-4

BACKGROUND: Insulinoma is a rare pancreatic neuroendocrine tumour characterised by inappropriate insulin secretion and recurrent hypoglycaemia. Owing to their small size and intrapancreatic localisation, insulinomas are frequently difficult to detect using conventional anatomical imaging techniques. Functional imaging based on positron emission tomography has therefore gained increasing interest, particularly through targeting of the glucagon-like peptide-1 receptor, which is highly overexpressed in most insulinomas. Among available tracers, gallium-68-labelled NODAGA-exendin-4 has demonstrated excellent diagnostic performance. However, its routine clinical implementation remains limited by the absence of a harmonised, robust and transferable radiosynthesis protocol compatible with hospital radiopharmacy practice. The aim of this work was to optimise and harmonise the automated preparation of gallium-68-labelled NODAGA-exendin-4 by systematically evaluating critical synthesis parameters and validating the optimised process across multiple commercially available gallium-68 generators. Using an automated synthesis module, key variables including precursor amount, labelling temperature and duration, formulation additives, workflow sequence and quality control conditions were investigated. The optimised protocol was subsequently validated using generators from three different manufacturers. RESULTS: Optimisation studies demonstrated that formulation-related parameters, particularly the post-labelling addition of polysorbate 20, resulted in improved radiochemical conversion and reduced residual activity within the synthesis cassette. An optimal precursor amount of 20 µg was identified as a compromise between radiochemical yield and clinical injectability constraints. Radiolabelling at 95 °C for 12 min ensured high conversion while reducing overall synthesis time. Validation runs showed excellent reproducibility, with non-decay-corrected yields ranging from 60 to 73% and decay-corrected yields reaching up to 93%, independent of generator type. Radiochemical purity consistently exceeded 95%, and all quality control parameters complied with established specifications. CONCLUSIONS: This study establishes a simplified, efficient and generator-independent automated synthesis of gallium-68-labelled NODAGA-exendin-4. By addressing key translational and regulatory constraints, the proposed protocol provides a practical foundation for the routine clinical implementation of glucagon-like peptide-1 receptor imaging in patients with suspected insulinoma.