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

Two new N-omega-fluoroalkyl analogs of 123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (123I]beta-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]beta-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.