Human Biodistribution and Radiation Dosimetry of 82Rb

Prior estimates of radiation-absorbed doses from Rb-82, a frequently used PET perfusion tracer, yielded discrepant results. We reevaluated Rb-82 dosimetry using human in vivo biokinetic measurements. Methods: Ten healthy volunteers underwent dynamic PET/CT (6 contiguous table positions, each with separate Rb-82 infusion). Source organ volumes of interest were delineated on the CT images and transferred to the PET images to obtain time-integrated activity coefficients. Radiation doses were estimated using OLINDA/EXM 1.0. Results: The highest mean absorbed organ doses (mu Gy/MBq) were observed for the kidneys (5.81), heart wall (3.86), and lungs (2.96). Mean effective doses were 1.11 +/- 0.22 and 1.26 +/- 0.20 mu Sv/MBq using the tissue-weighting factors of the International Commission on Radiological Protection (ICRP), publications 60 and 103, respectively. Conclusion: Our current Rb-82 dosimetry suggests reasonably low radiation exposure. On the basis of this study, a clinical Rb-82 injection of 2 x 1,480 MBq (80 mCi) would result in a mean effective dose of 3.7 mSv using the weighting factors of the ICRP 103-only slightly above the average annual natural background exposure in the United States (3.1 mSv).