DOSIMETRY OF COPPER-64-LABELED MONOCLONAL-ANTIBODY 1A3 AS DETERMINED BY PET IMAGING OF THE TORSO

We present biodistribution and dosimetry results for Cu-64-benzyl-TETA -MAb 1A3 from 15 human subjects injected with this tracer as determine d by serial PET imaging of the torso. Methods: PET imaging was used to quantify in vivo tracer biodistribution at two time points after inje ction. Absorbed dosimetry calculated using MIRD-11 and the updated MIR DOSES was compared with estimates obtained using rat biodistribution d ata. Results: By measuring activity concentrations in the torso, and e xtrapolating for the whole body using standard organ and tissue volume s, we were able to account for 93% of the injected radiopharmaceutical over a range of imaging times from 0 to 36 hr postinjection. Based on PET imaging and the MIRD-11 schema, the liver and spleen are the crit ical organs with average absorbed doses of 0.12 and 0.10 mGy/MBq (0.44 and 0.39 rad/mCi). The revised MIRDOSE3 scheme yields similar values for these and other organs but also results in a dose of 0.14 mGy/MBq (0.53 rad/mCi) to the heart wall. In the rat, the large intestine is t he critical organ at 0.14 mGy/MBq (0.52 rad/mCi), while liver and kidn eys each receive 0.11 mGy/MBq (0.41 rad/mCi). Some disparities in abso rbed doses determined by these methods are evident but are a result of dissimilar biodistributions in rats and humans. For most organs, rat extrapolated values are higher than the human measurements with PET. C onclusion: This study shows that torso PET imaging can quantitatively measure the whole-body biodistribution of a radiopharmaceutical as lon g as it has relatively slow pharmacokinetics.