Technetium-99m (Tc-99m) is the most used radioactive tracer with over 30 million tests per year done all over the world. When tagged to a pharmaceutical or biological marker, it helps evaluate, diagnose or manage cancer spread, blood flow and cardiac function; brain activity and thyroid disease; and detect osseous metastasis, fractures and infections (bone scan). Radiology professionals inject this radioisotope to gauge blood flow to the organs and detect cancer spread much earlier and with greater precision than many other methods, including PET or CT scan. Tc-99m, with a half-life of just 6 hours, is the most preferred radioactive tracer‚Äîit emits high energy 142.7 keV gamma rays, allowing very high resolution imaging without posing any danger of long-term radiation damage to the internal organs. Lately, Tc-99m supply chain has come under stress. In the January 21, 2011 issue of Science, Robert F. Service wrote that due to the 2009 temporary closure of NRU and Petten reactors and resulting shortage of Tc-99m, “physicians were forced to use less Tc-99m for many procedures, ration what scant supplies remained, and find less desirable substitutes.”
Tc-99m is a metastable (“m” for metastable) isotope of molybdenum-99 (Mo-99) which is a fission product of highly-enriched Uranium (U-235). Mo-99 has a half-life of 2.7 days; it is normally produced at Research Reactors around the world, and shipped encased in technetium generators to hospital radiopharmacies.
Mo-99 is currently made at five nuclear facilities around the world. Most of the Mo-99 used in the United States is imported from Chalk River, Ontario-based National Research Universal (NRU) reactor. NRU and High Flux Reactor (HFR) at Petten (in Netherlands) together supply nearly three-quarters of all worldwide demand for Mo-99, the rest coming from reactors in Belgium (BR2 reactor at Mol), France (Osiris reactor at Saclay), and South Africa (Safari reactor at Palindaba); Australian OPAL reactor in Sydney also makes some Mo-99. Both NRU and Petten reactors are half a century old (52- and 47-years old, respectively) and have had their share of shutdowns and repairs, disrupting supplies and creating real shortages. When NRU was closed for repairs between May 2009 and August 2011, the radiation departments all over the country found themselves looking for alternate sources, where there was none! The situation became worse when Petten reactor was also briefly closed in May 2009 to fix corroded pipes.
There is an urgency to the long-term Mo-99 supply situation, since the NRU reactor is slated to permanently close in 2015. The alternatives to using Tc-99m imaging are inadequate‚Äîdoctors could order CT or PET scans, but these methods expose patients to a much higher radiation dose; cost more; or provide relatively poor quality images. Several commercial and federal initiatives are attempting to address the looming Mo-99 shortage. In a recent article in The Scientist, Robert Schenter, CSO of Kennewick, Wash.-based Advanced Medical Isotope Corp., described two technological initiatives under development that may address Mo-99 shortage in the United States: Robert Schenter’s company is developing a proprietary method of producing Mo-99 by passing a beam of electrons through a tube containing deuterium oxide (heavy water) and U-235. Splitting of deuterium nuclei by photons (a result of electron beam) and the release of neutrons initiates U-235 fission and Mo-99 production; another company, Babcock & Wilcox Company, Lynchburg, Virginia, is developing a patented aqueous homogeneous reactor (AHR) technology that uses low-enriched uranium. In addition, GE Hitachi Nuclear Energy in Wilmington, North Carolina, is developing a neutron capture method that may eliminate the use of high-enriched U-235. Scientists at the National Measurement Standards in Ottawa, Canada, have recently developed a method to knock neutrons out of Mo-100 atoms using an electron linear accelerator to produce Mo-99; thus, eliminating the need to use highly-enriched Uranium. In the United States, two federal facilities can be tapped to meet emergency demand: the University of Missouri Research Reactor Center (MURR) and Annular Core Research Reactor (ACRR) at Sandia National Laboratories, Albuquerque, New Mexico. In September 2010, IAEA held a conference where various stake holder countries re-affirmed the goal of completely phasing out highly-enriched uranium (which can be diverted towards producing nuclear weapons) and developing alternate strategies to meet Mo-99 demand‚ÄîU.S. is a signatory to this agreement. Time is running out, but hopefully some of the initiatives above will mature before NRU and Petten are consigned to Smithsonian history along with Shuttles Challenger and Columbia.
Read more about author, Medical Writer and Cancer Biologist, Ajay Malik, PhD
Desperately Seeking Radioisotopes. Schenter RE. The Scientist. 2011 July 1; 25(7):26 | FullText |
Battling the Bottleneck: Critically Needed Diagnostic Isotope’s Supply Remains Uncertain. Kidambi M. IAEA Bulletin. 2011; 52(2) | PDF Link |
Medical Isotope Production Without Highly Enriched Uranium (2009). Nuclear and Radiation Studies Board (NRSB). [web page] National Academy of Sciences, Washington D.C., web site. http://www.nap.edu/openbook.php?record_id=12569&page=55. Accessed July 19, 2011.