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Radiation Dosimetry of β-Amyloid Tracers ¹¹C-PiB and ¹⁸F-BAY94-9172

¹ Centre for Positron Emission Tomography, Austin Hospital, Heidelberg, Victoria, Australia; and ² Bayer Schering Pharma, Berlin, Germany

Correspondence: For correspondence or reprints contact: Graeme J. O'Keefe, Centre for Positron Emission Tomography, Austin Hospital, Studley Rd., Heidelberg, Victoria 3084, Australia. E-mail: graeme.okeefe{at}petnm.unimelb.edu.au

β-Amyloid (Aβ) imaging has great potential to aid in the diagnosis of Alzheimer disease and the development of therapeutics. The radiation dosimetry of Aβ radioligands may influence their application; therefore, we calculated and compared the effective doses (EDs) of ¹¹C-PiB and a new ¹⁸F-labeled ligand, ¹⁸F-BAY94-9172. Methods: Attenuation-corrected whole-body scans were performed at 0, 15, 30, 45, and 60 min after injection of 350 ± 28 MBq (mean ± SD) of ¹¹C-PiB in 6 subjects and at 0, 20, 60, 120, and 180 min after injection of 319 ± 27 MBq of ¹⁸F-BAY94-9172 in 3 subjects. Coregistered CT was used to define volumes of interest (VOIs) on the PET images. The source organs were the brain, lungs, liver, kidneys, spleen, and vertebrae. The VOIs for the contents of the gallbladder, urinary bladder, lower large intestine, upper large intestine, and small intestine were also defined. Total activity in each organ at each time point was calculated by use of reference organ volumes. The resultant time–activity curves were fitted with constrained exponential fits, and cumulated activities were determined. A dynamic bladder voiding model was used. The OLINDA/EXM program was used to calculate the whole-body EDs from the acquired data. Results: For ¹¹C-PiB, the highest absorbed doses were in the gallbladder wall (44.80 ± 29.30 µGy/MBq), urinary bladder wall (26.30 ± 8.50 µGy/MBq), liver (19.88 ± 3.58 µGy/MBq), and kidneys (12.92 ± 3.37 µGy/MBq). The ED was 5.29 ± 0.66 µSv/MBq. For ¹⁸F-BAY94-9172, the highest doses were also in the gallbladder wall (132.40 ± 43.40 µGy/MBq), urinary bladder wall (24.77 ± 7.36 µGy/MBq), and liver (39.07 ± 8.31 µGy/MBq). The ED was 14.67 ± 1.39 µSv/MBq. Conclusion: The estimated organ doses for ¹¹C-PiB were comparable to those reported in earlier research. With the doses used in published studies (300–700 MBq), the EDs would range from 1.6 to 3.7 mSv. The ED of ¹⁸F-BAY94-9172 was 30% lower than that of ¹⁸F-FDG and, at the published dose of 300 MBq, would yield an ED of 4.4 mSv. The dosimetry of both Aβ radioligands is suitable for clinical and research applications.

Key Words: PET • radiation dosimetry • ¹¹C-PiB • ¹⁸F-BAY94-9172

COPYRIGHT © 2009 by the Society of Nuclear Medicine, Inc.

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