Radiation dose of [18F]DPA714 PET studies

Objectives [18F]DPA714 is a novel tracer of the 18-kDa translocator protein (TSPO). This protein is expressed in activated microglia, which are known to be activated during neuroinflammation. [18F]DPA714 may thus be used for quantification of neuroinflammatory reactions. The aim of this study was to assess the radiation dose in men with administration of [18F]DPA714.

Methods After IV bolus injection of 150 MBq [18F]DPA714, 4 successive whole body PET/CT studies (at 2, 32, 150 and 330 min p.i.) were acquired in 6 healthy controls. For 2 subjects a calibration source of 10 MBq was included in the field of view of the PET scanner for verification of image quantification. Regions of interest (ROI) were defined for all organs with increased uptake compared with background. Subsequently, percent injected dose (%ID) at each time point was calculated. Common ROI were brain, thyroid, spleen, liver, stomach and lungs. Residence times were derived by fitting %ID per time point to a function consisting of one to four exponentials, as appropriate. The residence time of the remainder of the body was obtained as the total body residence time minus the sum of the organ residence times. In addition three urine samples at 3 different time points were collected to determine urinary excretion.

Results Highest uptake of [18F]DPA714 was seen in the liver at 19% of injected dose, followed by the small bowel at 9.2%. The average effective dose from [18F]DPA714 equaled 0.021±0.002 (range 0.019 to 0.024) mSv/MBq. The organs receiving the highest average dose (dose equivalents) were the small intestine, kidneys and spleen, receiving 0.047, 0.046 and 0.044 mSv/MBq, respectively.

Conclusions The average effective dose from [18F]DPA714 equals 0.021±0.002 mSv/MBq which is similar to the dose associated with other F-18 labeled tracers such as [18F]FDG.

Research Support The study was financially supported by Bayer Schering Pharma AG, Berlin, Germany