Thorium: A Source of Multiple Medical Isotopes

Proton-irradiated thorium targets are successfully mined for therapeutic radium isotopes.

Image courtesy of Los Alamos National Laboratory

The radioisotope recovery flow sheet highlights how each step in the process removes specific elements from the solution while others pass to the next step, resulting in a pure final product.

The Science

Researchers developed a new method to recover radium isotopes for cancer treatment. The process begins with the dissolved proton-irradiated thorium target solution. The process then takes the solution through a series of columns. In each column, different isotopes bind to the different substrates the column contains. With the anticipated scale-up to large thorium targets, dozens of patient treatment doses would be available for recovery from a single production process. Los Alamos National Laboratory’s Isotope Team devised the method with collaborators from Brookhaven National Laboratory and Oak Ridge National Laboratory.

The Impact

The improvements result in high product yield and high purity for the isolated radium. The process is modular. This allows integration into an automatable multi-nuclide recovery flow sheet. Radium is now isolated from the same experiment as therapeutic isotopes actinium-225, protactinium-230, thorium-227, and uranium-230. The results appear in the Nature publisher’s open-access journal Scientific Reports. The study was selected as one of the top 100 read papers. It was selected out of more than 5000 chemistry papers published in 2017.   

Summary

Radium is a bone-seeking radioelement, due to its chemical similarity to calcium, the main component of hydroxyapatite, the bone mineral. Radium is thus “mistaken” for calcium in the body, which lets it accumulate in rapidly forming cells in bone metastases. Once incorporated into the cancer cells, the emitted alpha radiation promotes cancer cell death. Radium-223 is the first alpha-emitting isotope that obtained Food and Drug Administration approval for the treatment of cancer. Other radium isotopes of interest for preclinical research include radium-224 and radium-225. Researchers developed a novel methodology for the automated recovery of these radium isotopes from proton-irradiated thorium. Hundreds of millicuries of radium—corresponding to dozens of therapeutic patient doses—can be recovered in high yield and purity alongside other therapeutic isotopes during the same recovery process. The radium product obtained by this method is composed of radium-223, radium-224, and radium-225 and is suitable for chemistry applications (such as development of specialized ligands that hold radium with high selectivity inside a treatment compound) and investigation of possible treatment regimes. Radium-225 decays into actinium-225, so scientists can use the radium isotope as a “generator” of pure actinium-225 (no radium impurities that could decay to actinium isotopes) for pre-clinical or other research applications. While this approach alone does not produce quantities that are clinically relevant, it complements the DOE Isotope Program’s Tri-Laboratory activity that produces significant quantities of accelerator-produced actinium-225 for clinical trials and medical applications.

Contact

Michael E. Fassbender
Los Alamos National Laboratory
[email protected]; (505) 665-7306

Funding

Department of Energy (DOE), Office of Science, Isotope Development and Production for Research and Application subprogram within the Office of Nuclear Physics and Los Alamos National Laboratory’s Laboratory Directed Research and Development Program funded the research.

Publications

T. Mastren, V. Radchenko, A. Owens, R. Copping, R. Boll, J.R. Griswold, S. Mirzadeh, L.E. Wyant, M. Brugh, J.W. Engle, F.M. Nortier, E.R. Birnbaum, K.D. John, and M.E. Fassbender, “Simultaneous separation of actinium and radium isotopes from a proton irradiated thorium matrix.” Scientific Reports 7, 8216 (2017). [DOI: 10.1038/s41598-017-08506-9]

V. Radchenko, T. Mastren, C.A.L. Meyer, A.S. Ivanov, V.S. Bryantsev, R. Copping, D. Denton, J.W. Engle, J.R. Griswold, K. Murphy, J.J. Wilson, A. Owens, L. Wyant, E.R. Birnbaum, J. Fitzsimmons, D. Medvedev, C.S. Cutler, L.F. Mausner, K.D. John, S. Mirzadeh, and M.E. Fassbender, “Radiometric evaluation of diglycolamide resins for the chromatographic separation of actinium from fission product lanthanides.” Talanta 175, 318 (2017). [DOI: 10.1016/j.talanta.2017.07.057]

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Scientific Reports: Top 100 in Chemistry Collection

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