Room: Track 1
Purpose: Beta-emitting radiopharmaceuticals for cancer therapy has expanded rapidly in recent years following development of therapeutics for neuroendocrine tumors and prostate cancer. Copper-67 (t1/2:2.6d) is emerging as a promising radionuclide for radiopharmaceutical therapy due to (1) its chemical equivalence to the widely-established positron-emitting isotope 64Cu and (2) recently becoming available through the US Department of Energy Isotope Program. The purpose of this work is to establish the imaging and dosimetric characteristics of the 67Cu/64Cu theranostic pair, including the first literature report of 67Cu SPECT/CT imaging.
Methods: Copper-67 was produced by photon-induced reactions on isotopically-enriched 68Zn targets, followed by bulk separation of metallic 68Zn by sublimation and radiochemical purification by column chromatography. Gamma spectrometry was performed by efficiency-calibrated high-purity germanium (HPGe) analysis to establish radionuclidic purity, radioactive half-life, and absolute activity calibration. An anthropomorphic chest phantom, containing NEMA-sized spherical ‘tumors’, was filled with a tumor-to-background ratio of 5:1, using a total activity of 5mCi. SPECT/CT images were acquired (ME collimator, 15% energy window about 185keV photopeak, upper/lower 15% scatter windows, 180° non-circular orbit, 60 views/head, 20 seconds/view) and reconstructed (MIM SPECTRA Quant; OSEM3D). Recovery coefficients were calculated and compared against similar quantitative images acquired for ???Tc, ¹77Lu, and 64Cu.
Results: No radionuclidic impurities were observed. HPGe absolute activity measurements corroborated manufacturer-recommended dose-calibrator settings. The medium energy (ME) SPECT collimator was found to provide the best image quality when collecting images from the 185keV 67Cu gamma emission. Spatial resolution in the reconstructed images resembled those acquired with ???Tc and ¹77Lu, as evidenced by the similar measured SUVmean recovery coefficients – ranging from ~0.4 for 10mm tumors to ~0.8 for 37mm tumors.
Conclusion: Copper-67 imaging characteristics appear similar to clinically available SPECT/therapeutic radioisotopes. This confirms that post-administration dosimetry will be possible for 67Cu-based radiopharmaceuticals. The 67Cu/64Cu theranostic pair shows promise for clinical translation.
Funding Support, Disclosures, and Conflict of Interest: Parts of this work were supported by the Department of Energy Isotope Program.