FAP-targeted [68Ga]BED003-PET compared with [18F]DOPA-PET in patients with recurrent medullary thyroid carcinoma
Abstract
Aim Molecular imaging of recurrent or advanced medullary thyroid carcinoma (MTC) remains clinically challenging. [18F]DOPA-PET is an established reference standard, but its sensitivity is limited and dependent on tumour burden and biomarker levels. Fibroblast activation protein (FAP)-targeted PET has emerged as a promising imaging approach across several malignancies. This study aimed to compare the detection rate and quantitative imaging characteristics of [68Ga]BED003-PET, recently known as [68Ga]OncoFAP-DOTAGA, with [18F]DOPA-PET in patients with recurrent or advanced MTC. Methods Eight patients with histologically proven MTC and suspected recurrence or progression based on elevated calcitonin levels underwent both [18F]DOPA-PET and an additional [68Ga]BED003-PET. All patients presented with inconclusive findings in [18F]DOPA-PET. Comparative analyses were performed on a patient- and lesion-based level. Quantitative parameters included maximum and mean standardized uptake values (SUVmax/SUVmean), metabolic tumour volume (MTV), and maximum tumour-to-background ratios (TBRmax). Potential theranostic suitability was explored based on lesional FAP uptake. Results The median interval between PET acquisitions was 33 days (range, 7–56 days). In total, 35 tracer-avid lesions were detected. [68Ga]BED003-PET detected significantly more lesions than [18F]DOPA-PET (34/35 [97%] vs. 16/35 [46%], P < 0.001). 15 lesions (43%) were positive on both modalities, 19 (54%) were only [68Ga]BED003-positive, and 1 (2.9%) was only [18F]DOPA-positive. Quantitative analysis demonstrated significantly higher uptake and contrast for [68Ga]BED003, including higher blood-pool TBRmax than [18F]DOPA (6.02 vs. 2.23, Bonferroni adjusted P < 0.001). Conclusion In this small MTC cohort, [68Ga]BED003-PET demonstrated higher lesion detection and TBRs in patients with inconsistent findings in [18F]DOPA-PET. Prospective multicenter validation is warranted.