Dosimetry and first human experience with Zr-panitumumab.

Zr-panitumumab is a novel immuno-PET radiotracer. A fully humanized IgG2 antibody, panitumumab binds with high affinity to the extracellular ligand binding domain of EGFR. Immuno-PET with radiolabeled panitumumab is a non-invasive method that could characterize EGFR expression in tumors and metastatic lesions. It might also assist in selecting patients likely to benefit from targeted therapy as well as monitor response and drug biodistribution for dosing guidance. Our objective was to calculate the maximum dosing for effective imaging with minimal radiation exposure in a small subset. Three patients with metastatic colon cancer were injected with approximately 1 mCi (37 MBq) of Zr-panitumumab IV. Whole body static images were then obtained at 2-6 hours, 1-3 days and 5-7 days post injection. Whole organ contours were applied to the liver, kidneys, spleen, stomach, lungs, bone, gut, heart, bladder and psoas muscle. From these contours, time activity curves were derived and used to calculate mean resident times which were used as input into OLINDA 1.1 software for dosimetry estimates. The whole body effective dose was estimated between 0.264 mSv/MBq (0.97 rem/mCi) and 0.330 mSv/MBq (1.22 rem/mCi). The organ which had the highest dose was the liver which OLINDA estimated between 1.9 mGy/MBq (7.2 rad/mCi) and 2.5 mGy/MBq (9 rad/mCi). The effective dose is within range of extrapolated estimates from mice studies. Zr-panitumumab appears safe and dosimetry estimates are reasonable for clinical imaging.