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Biodistribution and Radiation Dosimetry of the Amyloid Imaging Agent ¹¹C-PIB in Humans

¹ Turku PET Centre, University of Turku, Turku, Finland; ² Turku PET Centre, Turku University Hospital, Turku, Finland; ³ GE Healthcare Medical Diagnostics, Chalfont St. Giles, United Kingdom; and ⁴ Turku Imanet Ltd., Turku, Finland

Correspondence: For correspondence or reprints contact: Juha O. Rinne, MD, PhD, P.O. Box 52, FIN-20521 Turku, Finland. E-mail: juha.rinne{at}tyks.fi

We investigated the biodistribution and radiation dosimetry of the PET amyloid imaging agent ¹¹C-PIB (¹¹C-6-OH-BTA-1) (where BTA is benzothiazole) in humans. Previous radiation exposure estimates have been based on animal experiments. A dosimetry study in humans is essential for a balanced risk–benefit assessment of ¹¹C-PIB PET studies. Methods: We used data from 16 different ¹¹C-PIB PET scans on healthy volunteers to estimate radiation exposure. Six of these scans were dynamic imaging over the abdominal region: 3 covering the upper abdomen and 3 covering the middle abdomen. On average, 489 MBq of ¹¹C-PIB (range, 416–606 MBq) were injected intravenously, and dynamic emission scans were recorded for up to 40 min. Two subjects had whole-body imaging over the entire body to illustrate the biodistribution. PET brain scans and blood and urine radioactivity measurements from our previous ¹¹C-PIB studies were also analyzed. Thirteen source organs and the remainder of the body were studied to estimate residence times and mean radiation-absorbed doses. The MIRD method was used to calculate the radiation exposure of selected target organs and the body as a whole. Results: There is a high degree of consistency between our human data and previous biodistribution information based on baboons. In our study, the highest radiation-absorbed doses were received by the gallbladder wall (41.5 µGy/MBq), liver (19.0 µGy/MBq), urinary bladder wall (16.6 µGy/MBq), kidneys (12.6 µGy/MBq), and upper large intestine wall (9.0 µGy/MBq). The hepatobiliary and renal systems were the major routes of clearance and excretion, with approximately 20% of the injected radioactivity being excreted into urine. The effective radiation dose was 4.74 µSv/MBq. Conclusion: The established clinical dose of ¹¹C-PIB required for 3-dimensional PET amyloid imaging has an acceptable effective radiation dose. This dose is comparable with the average exposure expected in other PET brain receptor tracer studies. ¹¹C-PIB is rapidly cleared from the body, largely by the kidneys. From the viewpoint of radiation safety, these results support the use of ¹¹C-PIB in clinical PET studies.

Key Words: PET • dosimetry • ¹¹C-PIB • ¹¹C-6-OH-BTA-1 • amyloid

COPYRIGHT © 2007 by the Society of Nuclear Medicine, Inc.

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