The ongoing global concern over a reliable and safe supply of radioactive isotopes for use in medical imaging could be alleviated by using accelerators, not nuclear reactors, for production, according to a perspective published online in the Jan. 28 issue of Nature.
A single radionuclide, technetium-99m ( 99mTc), is used in four-fifths of all such imaging procedures worldwide, and yet its supply is “remarkably fragile,” said Thomas Ruth, research scientist at TRIUMF and a senior scientist at the British Columbia Cancer Agency, both in Vancouver, Canada. TRIUMF is Canada's National Laboratory for Particle and Nuclear Physics.
In 2007, the unanticipated closure of the Chalk River facility in Canada slashed isotope stocks in North American hospitals by about 80 percent, causing much panic and the cancellation of 50,000 medical procedures over five weeks. The medical-isotope supply came back online, but the fragility of the system did not improve. In 2008, isotope shortages struck again in Petten, the Netherlands, and at Chalk River again. The Petten facility is not expected to reopen until February of this year, however it could be later.
The authors noted that both reactors are relatively old, and it is unclear how long they might last; there are plans to replace the Petten reactor in 2015, and Chalk River in 2016.
With no near-term or even long-term solutions being implemented that could provide a reliable and adequate supply for Europe and North America, Ruth and colleagues said that a possible alternative would be to use an accelerator to fire photons at relatively stable uranium isotope, uranium-238, instead of using a reactor to fire neutrons at the nuclear isotope uranium-235 ( 235U).
Ruth said that this also spurs the needed fission process, and while the production rate of (molybdenum-99) 99Mo is several orders of magnitude lower, it would be outweighed by the advantage of using safer materials.
“The challenge, then, is to generate a high-intensity beam of photons to produce commercially practical yields equivalent to those that can be generated by existing reactors,” the authors wrote.
If an accelerator were built within the next five years, it would take about three years and between $50 million U.S. and $125 million to build, and could be capable of producing enough 99Mo to meet Canada's needs, about 10 percent of North America’s needs, or 5 percent of global demand.
Several machines would be required to replace the existing reactors, but accelerators would be cheaper than reactors, which on average cost between $500 million U.S. and $1 billion, and do not have the same safety issues, the authors wrote.
Although 99mTc is the dominant medical isotope, that picture is changing, due to radioisotopes used for PET imaging, which are produced by accelerators. However, since these isotopes have a shorter half-life, hospitals must be equipped with their own cyclotrons, or have access to a regional facility and access is limited—only 2,000 of the 12,500 nuclear medicine installations in the United States have PET scanners. For every hospital to be equipped, the researchers said that cyclotrons and PET scanners will have to become more affordable, and governments will have to provide incentives.
In China, the government is investing directly in PET; prices for PET scanners are dropping rapidly, and cyclotrons are becoming more affordable with time, but it will be a decade before PET can outcompete SPECT, Ruth noted.
“Meanwhile, the major markets in the United States and Europe will continue to need 99Mo/99mTc. Decisions must be made quickly to determine whether the accelerator approach is viable and preferable to reactors while the replacement facilities can still be completed in a timely fashion,” the authors wrote.
“Although the production and delivery of radioisotopes for medicine has been in the private sector, the well-being of the citizens of the world requires significant involvement of both the private sector and governments at all levels. Action is required before it is too late,” Ruth and colleagues concluded.