Desperately Seeking Moly: Unreliable Supplies of Feedstock for Widely Used Medical Imaging Isotope Prompt Efforts to Develop U.S. Sources
Raloff, Janet, Science News
Of all the radioactive isotopes used in medical diagnostics, none plays a more pivotal role than technetium-99m. Each weekday, hospitals and clinics around the world use it to perform about 60,000 diagnostic procedures. Used in about 80 percent of nuclear imaging tests, the isotope is one of modern medicine's major tools for detecting, evaluating and treating cancers, heart disease and other serious illnesses. It helps doctors lengthen patients' lives.
Trouble is, Tc-99m itself has a very short life. Radioactive decay depletes it by half every six hours. The feedstock that supplies it--molybdenum-99--also has a rather short half-life (66 hours), so neither isotope can be stockpiled. New Mo-99, or "moly," must be made continually and delivered to imaging centers weekly.
But now the system for supplying the feedstock for nuclear imaging's star isotope is in peril. Just five geriatric nuclear reactors in Canada, Europe and South Africa produce roughly 90 percent of the global Mo-99 feedstock. At an average age of 47, those plants frequently shut down for the kinds of repairs commonly needed in reactors operating well past their prime. This summer such shutdowns led to technetium shortages so severe that U.S. officials now say efforts must begin, at long last, to establish American sources of these critical isotopes.
On again, off again
Problems began on May 15, when reactor operators found a small leak at the biggest Mo-99 producer, Canada's 52-yearold National Research Universal reactor near Chalk River, in Ontario. Inspections would eventually turn up widespread corrosion in the reactor's outer wall. Atomic Energy of Canada Limited, which runs the facility, recently announced that the reactor would not restart until well after the first of the year.
Routine maintenance brought down the second biggest Mo-99 producer--the Dutch High Flux Reactor in Petten--for roughly a month this summer. With the Canadian reactor offline as well, worldwide supplies of Mo-99 plummeted to about 30 percent of normal. Although the Petten reactor resumed operation in mid-August, its return to service will be short-lived. By March 20]0, the 47-yearold reactor must shut down for an estimated six months to undergo delayed repairs of corrosion damage.
The precarious health of Mo-99-production reactors had already spurred the Society of Nuclear Medicine to petition Congress for help in 2008. Led by Robert Archer of Los Alamos National Laboratory in New Mexico, then president of the society, these scientists and physicians campaigned for development of new, more reliable--and preferably domestic--sources of Mo-99. Even before this summer's technetium crisis emerged, the White House launched a federal interagency panel to look at developing homemade moly--perhaps, on an emergency basis, as early as spring 2010.
Such developments are fueling optimism, Atcher says, because the erratic availability of Tc-99m and its feedstock are "finally on the radar screen." Many U.S. companies, he adds, are now lining up to help bring moly production home.
Few good alternatives
A Society of Nuclear Medicine survey in August of 710 members found that 80 percent felt the impact of the summer's Tc-99m shortage. Only 31 percent of participants reported having enough isotope to perform at least three-quarters of their normal imaging workload; 5 percent were working at no more than 25 percent capacity. Of the respondents, 16 percent expected to "be down to zero percent capacity within a month."
Since the Canadian reactor's Mo-99 production stopped in May, Tc-99m supplies to Vanderbilt University Medical Center in Nashville have been only about two-thirds of what was requested, and sometimes have been as low as 25 percent of normal, says Jeff Clanton, who runs the radiopharmacy there.
What worries him most: the Petten reactor's long outage beginning next spring--especially if the Canadian reactor isn't back in operation. …