|Shortage of Radioisotopes Threatens Medical Research and Treatment|
|By Robert E. Schenter, PhD|
|Thursday, 12 May 2011 01:22|
Unfortunately, the supply of Mo-99 and other radioisotopes has been unreliable at best. All of the Mo-99 used in the US is imported, with the main source being the National Research Universal Reactor at AECL, Ltd., located in Chalk River, Ontario. A shutdown for repairs in May 2009 contributed to a global radioisotopes shortage; while the reactor has been back in operation since August 2010, it is scheduled for closure in 2015.
The shortage is already having a negative effect on research programs. For example, as reported in the Hamilton (Ontario) Spectator last year, it is damaging neutron beam research at McMaster University and preventing students from receiving proper training. Professor Maikel Rheinstadter told the newspaper that if no plans are made to replace the Chalk River reactor soon, Canada is under threat of a “massive brain drain to the United States.”
Apart from its effects on research at McMaster and possibly other institutions, the crisis is compromising treatment options and is showcasing a critical gap in the supply chain. Although the US has many domestic reactors that could produce the radioisotopes, they do not have the necessary processing facilities nor the capacity to take time away from other projects to produce Mo-99. As a result, new production strategies are desperately needed. For some procedures, there’s simply no alternative, and without a reliable domestic supply of isotopes, nuclear medicine would severely limit doctors’ ability to diagnose and treat many diseases.
Already, some clinicians have switched to using thallium-201, which went out of favor about 15 years because Mo-99/technetium-99m has better imaging characteristics. Additionally, physicians are finding it harder to get their hands on iodine-131, another radioisotope that is used to treat thyroid cancer, Graves’ disease and hyperthyroidism. Alternatives for many procedures exist, including CT and PET scanning, using radioisotopes not made in nuclear reactors, but these have drawbacks ranging from increased cost and greater radiation burden to lower image quality.
Advanced Medical Isotope Corporation hopes to commercialize a proprietary Mo-99 production method initially conceived by University of Missouri researchers. The method involves a squat, meter-long vessel containing heavy water (deuterium oxide) and uranium. Shooting a beam of high-energy electrons at a tungsten target produces bremsstrahlung. The bremsstrahlung photons then rip apart deuterium, releasing neutrons. As these neutrons hit uranium, they’ll cause it to fission, producing some Mo-99. To boost the efficiency of the system to produce very high activity (3000 6-day Ci/week) and high specific activity (SPA) Mo-99, the vessel may be blanketed with a material that acts like a neutron mirror. The material should reflect any unreacted neutrons back and forth within the vessel, thereby increasing their chance of hitting a uranium atom. Calculations indicate a blanket of polyethylene would work well, potentially increasing the effective flux of neutrons more than a thousand times.
Some argue that we have a moral imperative to provide an adequate supply of life-saving medical isotopes here on American soil. Doing so will save tens of millions of dollars for the healthcare market, which already spends about $128 billion per year on cancer. The lives that might be saved will make this a worthy endeavor indeed.
Robert E. Schenter is Chair Emeritus, Chief Science Officer and Member of Scientific Advisory Board of Kennewick, WA-based Advanced Medical Isotope Corp. (www.isotopeworld.com), a company engaged in the production and distribution of medical isotopes.