Repeatability of semi-quantitative [68Ga]Ga-FAPI-46 PET/CT measurements in pancreatobiliary cancers
a test-retest study
Rutger B. Henrar (Cancer Center Amsterdam, Vrije Universiteit Amsterdam)
Matthijs C.F. Cysouw (Vrije Universiteit Amsterdam, Cancer Center Amsterdam)
Xavier Palard-Novello (Université de Rennes, Vrije Universiteit Amsterdam, Cancer Center Amsterdam)
Lothar A. Schwarte (Vrije Universiteit Amsterdam, Cancer Center Amsterdam)
Pieter G.H.M. Raijmakers (Cancer Center Amsterdam, Vrije Universiteit Amsterdam)
Lioe Fee de Geus-Oei (Leiden University Medical Center, TU Delft - Applied Sciences, University of Twente)
Alexander L. Vahrmeijer (Leiden University Medical Center)
Geert Kazemier (Vrije Universiteit Amsterdam, Cancer Center Amsterdam)
Rutger Jan Swijnenburg (Cancer Center Amsterdam, Vrije Universiteit Amsterdam, Amsterdam UMC)
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Abstract
Purpose: Radiolabelled fibroblast activation protein inhibitors (FAPI) are promising molecular imaging tracers for the diagnosis and staging of pancreatobiliary cancer. To enable treatment response assessment with [68Ga]Ga-FAPI-46, the day-to-day variability of its uptake must be defined. This study aimed to determine the repeatability of semi-quantitative [68Ga]Ga-FAPI-46 PET/CT measurements in pancreatobiliary cancers. Methods: Patients with pathologically confirmed pancreatobiliary cancer (pancreatic ductal adenocarcinoma (PDAC) or cholangiocarcinoma (CCA)) were included. Patients underwent two [68Ga]Ga-FAPI-46 PET/CT scans, within 7 days, without any treatment before or between scans. Static long axial field-of-view (LAFOV) PET/CT scans were performed 60 min post-injection of [68Ga]Ga-FAPI-46 (EARL2-compliant reconstruction). Suspected malignant lesions were semi-automatically delineated (local background-adjusted 50% isocontour of the peak standardised uptake value (SUV)) and semi-quantitative measurements were extracted (SUVmean, SUVpeak and SUVmax). Tumour-to-background ratios (TBR) were also calculated. Repeatability was assessed using the repeatability coefficient (RC) and the intraclass correlation coefficient (ICC). Results: Twelve patients were included (seven PDAC, three perihilar CCA and two intrahepatic CCA). The median injected dose was 216 MBq (interquartile range (IQR) 167–266 MBq) and the median uptake time was 60 min (range 60–68). In total, 70 FAPI-positive lesions were delineated. The RCs of SUVmean, SUVpeak and SUVmax were 23.7%, 23.9% and 29.8%, respectively. For the blood pool adjusted TBRmean, TBRpeak and TBRmax, the RC’s were 21.6%, 20.8% and 28.0%, respectively. All ICCs were above 0.98. Conclusion: Semi-quantitative measurements of [68Ga]Ga-FAPI-46 PET/CT have an excellent repeatability and can potentially be used in future studies to assess treatment response in pancreatobiliary cancers.