Biodistribution and radiation dosimetry of the A1 adenosine receptor ligand 18F-CPFPX determined from human whole-body PET

Purpose F-18-8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine (F-18-CPFPX) is a potent radioligand to study human cerebral A(1) adenosine receptors and their neuromodulatory and neuroprotective functions with positron emission tomography (PET). The purpose of this study was to determine the biodistribution and the radiation dose of F-18-CPFPX by whole-body scans in humans. Methods Six normal volunteers were examined with 12 whole-body PET scans from 1.5 min to 4.5 h after injection. Volumes of interest were defined over all visually identifiable organs, i.e. liver, gallbladder, kidneys, small intestines, heart, and brain to obtain the organs' volumes and time-activity curves (TACs). TACs were fitted with exponential functions, extrapolated, multiplied with the physical decay and normalized to injected activities so that the residence times could be computed as area under the curve. Radiation doses were calculated using the OLINDA/EXM software for internal dose assessment in nuclear medicine. Results The liver uptake shows peak values (decay-corrected) of up to 35% of the injected radioactivity. About 30% is eliminated by bladder voiding. The highest radiation dose is received by the gallbladder (136.2 +/- 66.1 mu Sv/MBq), followed by the liver (84.4 +/- 10.6 mu Sv/MBq) and the urinary bladder (78.3 +/- 7.1 mu Sv/MBq). The effective dose was 17.6 +/- 0.5 mu Sv/MBq. Conclusions With 300 MBq of injected F-18-CPFPX a subject receives an effective dose (ICRP 60) of 5.3 mSv. Thus the effective dose of an F-18-CPFPX study is comparable to that of other F-18-labelled neuroreceptor ligands.