Radiation dosimetry for the reactive astrogliosis positron emission tomography tracer [¹⁸F]SMBT-1 in healthy human

Abstract Background [¹⁸F]SMBT-1 is a prominent positron emission tomography (PET) tracer developed as a selective and reversible imaging probe for monoamine oxidase B (MAO-B). MAO-B is overexpressed in reactive astrocytes and serves as a surrogate biomarker for astrogliosis, a component of neuroinflammation. However, internal radiation dosimetry data, have not been demonstrated for [¹⁸F]SMBT-1 in humans. Thus, the current study aimed to evaluate the whole-body absorbed dose and estimate the radiation exposure of [¹⁸F]SMBT-1 in each organ and the whole-body effective dose in healthy individuals. Results Dynamic whole-body [¹⁸F]SMBT-1 PET scans, consisting of 9 consecutive scans over 6 h following intravenous injection of [¹⁸F]SMBT-1 (168.0 ± 17.8 MBq), in 6 healthy volunteers (4 men and 2 women, aged 21–63 years) demonstrated high [¹⁸F]SMBT-1 uptake in the liver and gallbladder. Calculations using OLINDA/EXM software on regions of interest (ROIs) data, taken from the first 5 scans for 30 min and the following 4 scans for approximately 5 h, demonstrated that the absorbed dose in the gallbladder wall was much higher than that in the other organs in both men and women. A discrepancy was observed between the calculated results of the estimated absorbed doses for the urinary bladder walls based on the PET and urine sample data, respectively. The estimated effective dose was 2.41 × 10 − 2 ± 2.41 × 10 − 3 mSv/MBq for all participants, and was 2.25 × 10 − 2 and 2.74 × 10 − 2 mSv/MBq for men and women, respectively, when urine samples were measured. The whole-body effective doses did not differ substantially between the calculations based on PET-derived bladder activity and those based on urine sample data. Conclusions The estimated effective dose of [¹⁸F]SMBT-1 calculated using OLINDA/EXM was similar to that of other clinically used amyloid PET tracers. [¹⁸F]SMBT-1 PET examination has a good dosimetry profile and a radiation burden similar to that of other commonly used clinical PET tracers. Extremely high radiation exposure to the gallbladder wall can be reduced by a certain intervention such as eating fatty meals. Trial registration UMINCTR, UMIN000041176. Registered 19 August 2020, https//center6.umin.ac.jp/cgiopenbin/ctr/ctr_view.cgi? recptno=R000047016.