232Th-Spallation-Produced 225Ac with Reduced 227Ac Content.

ABSTRACT

Recent clinical results have demonstrated remarkable treatment responses of late-stage cancer patients when treated with alpha-emitting radionuclides such as actinium-225 (225Ac). The resulting intense global effort to produce greater quantities of 225Ac has triggered a number of emerging technologies to produce this rare, yet important, radionuclide. Accelerator-based methods for increasing global 225Ac production capacity have focused on the high energy (>100 MeV) proton irradiation of thorium, despite the coproduction of the undesirable 227Ac byproduct at 0.1-0.3% of the 225Ac activity. We at TRIUMF have developed a process for the production of a 225Ra/225Ac generator from irradiated thorium that results in an 225Ac product with reduced 227Ac content. 225Ac was separated from irradiated thorium and coproduced radioactive spallation and fission products using a thorium peroxide precipitation method followed by cation exchange and extraction chromatography. Stable and radioactive tracer studies demonstrated the ability of this method to separate Ac from most other elements, providing a directly produced Ac product with measured 227Ac content of (0.15 ± 0.04)%. A second, indirectly produced Ac product with 227Ac content of <7.5 × 10-5% is obtained by repeating the final extraction chromatography step with the 225Ra-containing fraction. The 225Ra-derived 225Ac showed similar or improved quality compared to the initial, directly produced 225Ac product in terms of chemical purity and radiolabeling capability, the latter of which was comparable with other 225Ac sources reported in the literature.