OC03 - [18F] Fluorethyltyrosine positron emission tomography in corticotroph pituitary adenomas

Background/Introduction Conventional magnetic resonance imaging accurately detects up to 75% of corticotroph adenomas. Therefore, in a substantial number of patients, exploratory pituitary surgery is still required. This carries the risk of either unnecessarily extensive resection—potentially leading to postoperative hypopituitarism—or incomplete tumor removal, resulting in persistent hypercortisolism. Purpose To improve surgical planning and outcomes, we aimed to evaluate the diagnostic potential of [18F]fluoroethyltyrosine positron emission tomography/computed tomography ([18F]FET PET/CT) in localizing ACTH-secreting pituitary adenomas in patients with newly diagnosed Cushing’s disease. Methods [18F]FET PET/CT was performed in all patients with a first diagnosis of ACTH- dependent Cushing’s disease treated at the Endocrinology Department of LMU Hospital between July 2024 and March 2025, as well as in patients with recurrent disease who consented to PET/CT imaging. Dynamic PET/CT acquisitions were conducted 0–40 minutes after intravenous administration of [18F]FET (mean dose: 166 ± 19 MBq). Image analysis included both visual evaluation and quantitative assessment of maximum tumor-to-background ratios (TBRmax), calculated as the ratio of the maximum standardized uptake value (SUVmax) of the pituitary lesion to the mean SUV (SUVmean) of the right frontal and temporal lobes. Image processing and analysis were performed using Hermia Hybrid Viewer, PDR 6.1.4 (Hermes Medical Solutions, Stockholm, Sweden). Numerical data are presented as median values with interquartile ranges (IQR). Results A total of 28 patients underwent [18F]FET PET/CT, including 17 with newly diagnosed ACTH-dependent Cushing’s disease and 11 with recurrent disease. Focal intrasellar radioligand uptake was observed in 16 of 17 cases with first diagnosis and 10 of 11 patients with recurrent disease. The median TBRmax was 7.0 (IQR 6.0–8.0) in patients with first diagnosis and 7.0 (IQR 6.0–8.2) in patients with recurrent disease. Of the 17 patients with a first diagnosis, 10 underwent transsphenoidal surgery, including 2 without a visible MRI correlate. In all 10 operated patients, the [18F]FET PET/CT localization was confirmed intraoperatively. Histopathological confirmation and biochemical remission was achieved in 9 of these cases. Conclusion(s) [18F]FET PET is effective in localising pituitary adenomas in Cushing‘s disease and can add valuable information to MRI and inferior petrosal sinus sampling