Alpha particle-emitting isotopes are being investigated for use in radioimmunotherapeutic applications for treating cancer. Of the prospective α-emitters, 225Ac isotope with a short 10 day half-life is of major interest. 225Ac is being investigated mainly to produce 213Bi in a reusable generator and alone as a potential radionuclide for attachment to vectors for targeted treatment of cancer. The main source of 225Ac is from the long-lived parent 229Th (half-life= 7340 years). However, this provides limited quantities of 225Ac that are insufficient for the current pre-clinical and clinical research demand. Therefore, an alternative method for the production of 225Ac based on 229Th spallation is being evaluated. The Medical Isotope Research and Production (MIRP) facility at Brookhaven National Laboratory is investigating high energy proton irradiation of thorium targets to produce 225Ac. Thorium targets irradiated with proton energies at 90 to 200 MeV produces 400 isotopes resulting from thorium fission. The conventional method for 225Ac purification is very time consuming and generates a large amount of waste. The aim of this work is to evaluate new methods for the separation of Ac from Th. We investigated the use of polyoxometalates (POMs) and 3,4,3-Li(1,2-HOPO), for the selective separation of Th from 225Ac using liquid-liquid extraction methods. Several parameters were studied (extracting agents, organic solvent, extracting agent dilution) using batch studies for defining the best conditions. While octylamine has no extraction behavior for Th, our results show that, POMs form an ion pair complex with octylamine. The latter extracts Th to organic phase with 100% 225Ac remaining in the aqueous phase. A second extraction method was studied utilizing lanthanum as a surrogate for 225Ac. 3,4,3-Li(1,2-HOPO) was used for the selective complexation of Th in HNO3 aqueous phase leading to La extraction by 10% HDEHP in xylene. Then, La is back-extracted from HDEHP by using 7M HCl. This process provided 78% recovery of La. The optimized processes leads to the selective separation of Th from 225Ac/La using POMs and 3,4,3-Li(1,2-HOPO) with a global recovery yield of 78-100 %.

New approach for the isolation of 225Ac isotope from proton irradiated Th target

255th National Meeting (2018)

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