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Mol Imaging Biol. 2008 Nov-Dec;10(6):341-8. doi: 10.1007/s11307-008-0160-5. Epub 2008 Aug 5.

Radiation dose estimates for [18F]5-fluorouracil derived from PET-based and tissue-based methods in rats.

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Molecular and Medical Pharmacology, Ahmanson Biological Imaging Division, UCLA Medical Center, Los Angeles, CA 90095-6942, USA.



Radiation dosimetry assessment often begins with measuring pharmaceutical biodistribution in rodents. The traditional approach to dosimetry in rodents involves a radioassay ex vivo of harvested organs at different time points following administration of the radiopharmaceutical. The emergence of small-animal positron emission tomography (PET) presents the opportunity for an alternative method for making radiodosimetry estimates previously employed only in humans and large animals. In the current manuscript, normal-tissue absorbed dose estimates for the 18F-labeled chemotherapy agent [18F]5-fluorouracil ([18F]5-FU) were derived by PET imaging- and by tissue harvesting-based methods in rats.


Small-animal PET data were acquired dynamically for up to 2 h after injection of [18F]5-FU in anesthetized rats (n=16). Combined polynomial and exponential functions were used to model the harvesting-based and imaging-based time-activity data. The measured time-activity data were extrapolated to modeled (i.e., Standard Man) human organs and human absorbed doses calculated.


Organ activities derived by imaging-based and by harvesting-based methods were highly correlated (r>0.999) as were the projected human dosimetry estimates across organs (r=0.998) obtained with each method. The tissues calculated to receive highest radiation dose by both methods were related to routes of excretion (bladder wall, liver, and intestines). The harvesting-based and imaging-based methods yielded effective dose (ED) of 2.94E-2 and 2.97E-2 mSv/MBq, respectively.


Small-animal PET presents an opportunity for providing radiation dose estimates with statistical and logistical advantages over traditional tissue harvesting-based methods.

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