Dosimetry of the Dopamine Transporter Radioligand 18F-FPCIT in Human Subjects

This study was designed to evaluate the radiation dosimetry in human subjects for a new radiopharmaceutical, N-(3-18F-fluoropropyl)-2-carbomethoxy-3-(4-iodophenyl)nortropane (18F-FPCIT). The goal was to determine a limiting dose consis-tent with accepted guidelines for use in clinical studies and to compare the radiation burden with other agents such as 123I-FPCIT, 18F-fluorodopa, and 18F-FDG. Methods: Dynamic PET scans of the urinary bladder were obtained in 6 subjects; 2 subjects had brain scans and 5 subjects had scans of the thorax or abdomen. Regions of interest were placed over composite images of each organ for which activity was visualized to gen-erate time–activity curves. Doses were calculated from resi-dence times using the MIRDOSE3 program. Results: The crit-ical organ for dosimetry is the urinary bladder wall with a dose of 0.0586 0.0164 mGy/MBq. The dose comes primarily (97.2%) from activity in the urinary bladder contents. The dose is lower than any of the other agents used commonly in PET to assess dopaminergic function. The effective dose equivalent (0.0120 mGy/MBq) is also lower than comparable compounds. Conclusion: 18F-FPCIT has favorable dosimetry when com-pared with other agents used to study dopaminergic function. Doses as high as 853 MBq (23 mCi) may be given to adult patients and remain within accepted guidelines