Very high specific activity erbium ¹⁶⁹Er production for potential receptor-targeted radiotherapy

Erbium Er-169 is one of the most interesting radiolanthanides for new potential receptor-targeted beta(-) therapy applications due to its low energy beta(-) emissions, very low intensity gamma rays and the possibility to use Ga-68 or Sc-44 as companion for diagnostic in a theranostics approach. Currently it can be produced in reactors through the neutron activation of highly enriched Er-168. The low specific activity of the produced carrier-added Er-169 is limiting its use for receptor-targeted therapy. Nonetheless it is used for radiosynoviorthesis of small joints. The aim of this work is to develop a new large-scale production method for the supply of very high specific activity Er-169. Highly enriched Er-168 target has been irradiated at ILL nuclear reactor and shipped to CERN-MEDICIS. There, the irradiated sample has been mass separated in order to isolate Er-169 from the high amount of remaining stable Er-168. The proof of principle for a preclinical dose production has been demonstrated with a collection of approximate to 17 MBq. The specific activity obtained was approximate to 240 GBq/mg (approximate to 200 times higher than the product obtained at End of Bombardment - EOB) and the overall separation efficiency was approximate to 0.2%. Several improvements for the future have been identified and are promising. One of them is the installation of the new laser laboratory at CERN-MEDICIS that will allow to improve the selective ionization of erbium atoms leading to an increase of the efficiency of the method. This method can provide the supply of high specific activity Er-168, first for preclinical studies, and opens also the potential for future large-scale supply.