Investigation of a tellurium-packed column for isolation of astatine-211 from irradiated bismuth targets and demonstration of a semi-automated system.

Astatine-211 is an attractive radionuclide for use in targeted alpha therapy of blood-borne diseases and micrometastatic diseases. Efficient isolation methods that can be adapted to robust automated At isolation systems are of high interest for improving the availability of At. Based on the early studies of Bochvarova and co-workers involving isolation of At from irradiated thorium targets, we developed a method for At isolation from bismuth targets using tellurium-packed columns. Dissolution of irradiated bismuth targets is accomplished using HNO; however, At is not captured on the Te column material in this matrix. Our method involves slow addition of aqueous NHOH·HCl to the Bi target dissolved in HNO to convert to a HCl matrix. The amount of NHOH·HCl was optimized because (1) the quantity of NHOH·HCl used appears to affect the radiolabeling yield of phenethyl-closo-decaborate(2-) (B10)-conjugated antibodies and (2) reducing the volume of NHOH·HCl solution can effectively shorten the overall isolation time. A proof-of-concept semi-automated process has been demonstrated using targets containing ~0.96 GBq (~26 mCi) of At. High isolation yields (88-95%) were obtained. Radiochemical purity of the isolated At was assessed by radio-HPLC. Concentrations of Bi and Te contaminants in the At and the astatinated antibodies were evaluated using ICP-MS.