Florbetapir is one of several 18F-labeled amyloid plaque imaging tracers for positron emission tomography (PET). As the bio-distribution and radiation dose of PET tracers in human research are important for estimating the relative risks and benefits, a study was conducted to obtain this information on florbetapir.
Nine cognitively normal subjects (six females and three males, age 58 ± 10 years, weight 81 ± 17 kg) received an intravenous bolus injection of 395 ± 27.9 MBq of florbetapir, and whole-body emission scans were performed over approximately 6 h. Computed tomography scans were acquired for attenuation correction. Volumes of interest (VOIs) for source organs including the brain, liver, lung, heart wall, and vertebrae were defined on the PET images. The VOIs of the gallbladder, urinary bladder, and large and small intestines were also defined. Using reference man organ volumes (ICRP 30), total activity was calculated per organ for each time point. The resultant time-activity curves (TACs) were fitted with constrained exponentials. Kinetic data were entered into OLINDA/EXM software to calculate dose estimates; the dynamic urinary bladder and ICRP 30 GI tract models were employed. The effective dose (ED) for each subject was estimated from the acquired data using the adult model.
The mean ED determined for nine healthy volunteers was 18.60 ± 4.26 μSv/MBq or 6.88 mSv for a 370-MBq dose. The organs that received the highest radiation absorbed doses were the gallbladder, upper large intestine, small intestine, liver, and urinary bladder at 143.0 ± 80.20, 74.50 ± 34.20, 65.50 ± 29.60, 64.40 ± 22.10, and 27.10 ± 11.70 μSv/MBq, respectively.
The ED for florbetapir has been calculated for nine healthy volunteers. At a dose of 370 MBq florbetapir, the total average ED is approximately 6.88 mSv.