Image courtesy of Los Alamos National Laboratory
Selenium (grey allotrope): a micronutrient essential for the human body. The margin of safety between essential and toxic, however, is narrow for this sulfur-like metalloid. One of selenium’s radioactive isotopes, 72Se, decays further into arsenic-72, a radiation source for medical imaging.
Bombarded with charged particles, chemical elements undergo conversion (“transmutation”) into small amounts of other elements. Such accelerator induced isotope formation has enabled new methodologies of making self-contained delivery systems for the radioisotope 72As for future clinical applications.
Positron emission tomography (PET) is a powerful technique to image lesions and biological processes using radioactive (positron emitting) isotopes. Researchers from Los Alamos National Laboratory (LANL) and the University of Missouri developed a new method to obtain a source for a radioisotope that allows for the tracking of biological processes with longer localization times: the selenium-72/arsenic-72 generator may provide clinicians with new 26 hour half-life in-vivo tracers for diagnostics and the study of diseases.
Similar to an electrical battery that supplies energy for a certain time period, a radionuclide generator, dubbed a “cow” by radiochemists, continually supplies a short-lived isotope that can be periodically separated (“milked”) for further application. When accelerated protons hit a body of sodium bromide—a white, crystalline compound similar to table salt—radioactive isotopes of the element selenium are formed in a nuclear reaction. One of these isotopes, 72Se (half-life 8.5 days), functions as a source of an imaging isotope, arsenic-72 (half-life 26 hours). This product, ironically an isotope of the infamous poison element arsenic, can be used to visualize slower biological processes, track viral infections or locate tumors in the human body. Researchers from LANL and the University of Missouri developed a technique to extract 72Se from irradiated sodium bromide and designed new methodologies to fix this 72Se on a solid support “cow” that can be “milked” to provide 72As for the labeling of biomolecules. Such biomolecules then serve as vehicles to transport this positron-emitting isotope to a specific location in the human body to enable diagnostic imaging.
Dr. Michael E. Fassbender
Los Alamos National Laboratory
Department of Energy, Office of Science, Nuclear Physics, Isotope R&D collaborative Grant No. DE-SC0003851.
Trainee support from the National Science Foundation under IGERT award DGE-0965983.
NIBIB Training Grant NIBIB 5 T32 EB004822.
D. E. Wycoff, M. D. Gott, A.J. DeGraffenreid, R. P. Morrow, N. Sisay, M. F. Embree, B. Ballard, M. E. Fassbender, C. S. Cutler, A. R. Ketring, S. S. Jurisson, Chromatographic separation of selenium and arsenic: A potential 72Se/72As Generator“, J. Chromatography A, 1340, 109 (2014).
M.E. Fassbender, B.D. Ballard, Se-72/As-72 generator system based on Se extraction/ As reextraction“, U.S. Patent # 8,529,873, September 10, 2013.
B. Ballard, F. M. Nortier, E. R. Birnbaum, K. D. John, D. R. Phillips and M. E. Fassbender, Radioarsenic from a Portable Se-72/As-72 Generator: A Current Perspective“,
Curr. Radiopharm. 5(3), 264 (2012).
B. Ballard, D. Wycoff, E.R. Birnbaum, K.D. John, J.W. Lenz, S.S. Jurisson, C.S. Cutler, F.M. Nortier, W.A. Taylor, M.E. Fassbender, „Selenium-72 Formation via natBr(p,x) Induced by 100 MeV Protons: Steps Towards a Novel 72Se/72As Generator System“, Appl. Radiat. Isot. 70(4), 595 (2012).
University, DOE Laboratory