Radiation dosimetry of [18F]PBR111

Objectives [¹⁸F]PBR111 is a novel PET tracer showing selective uptake by peripheral benzodiazepine receptors which may be useful for detecting inflammatory response in the brain. The aim of this preclinical study is to estimate the radiation dose to humans based on biokinetics in a baboon model.

Methods 150MBq of [¹⁸]PBR111 was given by i.v. injection under anaesthesia to an adult male baboon following a CT scan from head to thighs (Siemens Biograph TrueV-HD PET-CT). Whole body PET scans were acquired for 5 mins at 2 mins and then every 15 mins p.i. for two hours. Persistent uptake was seen in brain, myocardium, bone marrow and testes. Activity was excreted by both renal (6%) and hepatobiliary (14%) pathways. Regions were drawn on the coronal PET sections around whole organs and within L4, L5 vertebrae (assumed 6.8% of total marrow). Activity in the heart region was assigned to the heart wall. Activity in the liver after 2 mins was obtained by scaling from the right lobe to exclude biliary uptake. Net activity in the abdomen minus delineated organs was used as input to the small intestine in the ICRP model for the GI tract. Radiation doses were calculated from a least squares fit of the decay-corrected time-activity curves (OLINDA/EXM).

Results Organ doses mGy per MBq administered:

Results Biliary excretion resulted in highest organ doses.

Conclusions The radiation dosimetry of [¹⁸F]PBR111 is similar to that of other ¹⁸F ligands, with an effective dose from 350MBq injected of 6.7mSv to 7mSv for voiding intervals from 1 to 2.5h respectively.