Human biodistribution and dosimetry of iodine-123-fluoroalkyl analogs of β-CIT

Two new N-ω-fluoroalkyl analogs of [¹²³I]2β-carbomethoxy-3β-(4-iodophenyl)tropane ([¹²³I]β-CIT), the fluoroethyl and fluoropropyl compounds ([¹²³I]FE-CIT and [¹²³I]FP-CIT, respectively), have been shown to have faster kinetics and better selectivity for the dopamine transporter than [¹²³I]β-CIT. We examined the organ biodistribution and radiation safety of these two compounds in six healthy volunteers who received an injection with each of the two compounds 2 weeks apart. Data were obtained on the Strichman 860 whole-body scanner. Transmission scans were obtained in all subjects prior to the injection of the radiotracer with a line source and used to derive organ-specific attenuation correction factors. Whole-body planar images were acquired every hour for the first 6 h, and at 24 h. Attenuation-corrected regional conjugate counts were converted into units of activity using a calibration factor obtained for each subject by dividing whole-body conjugate decay-corrected counts from the first acquisition by the injected activity. Radiation dose estimates were on average higher for [¹²³I]CIT-FE than for [¹²³I]CIT-FP, with the lower large intestine receiving the highest exposure: 0.15 ± 13% mGy/MBq (mean ±COV)and 0.12 ± 14% mGy/MBq for [¹²³I]FE-CIT and [¹²³I]FP-CIT, respectively, followed by the upper large intestine and the spleen.