Nuclear mattersMedical isotopes could be made without a nuclear reactor

Canadian researchers are racing to perfect a safe, clean, inexpensive, and reliable method for making isotopes used in medical-imaging and diagnostic procedures.

The new method does not require a nuclear reactor and could therefore eliminate future shortages of technetium-99m — the most widely used medical isotope today.

Until recently, the National Research Universal (NRU) reactor at Chalk River, Ontario, produced almost 50 percent of the world’s supply of medical isotopes. Then in May 2009, the NRU was shut down for repairs.

This halt in operations, combined with several delays in its restart, contributed to a global isotopes shortage. While the reactor has been back in operation since August 2010, it is scheduled for closure by 2016.

The Engineer reports that last June the Government of Canada announced a $35 million program to promote research into alternative methods of producing medical isotopes. Backed by NRC and other collaborators, the Canadian Light Source submitted one of four successful proposals under this research program to explore the technical and economic feasibility of using an electron linear accelerator to produce molybdenum-99 (Mo-99) — the “parent isotope” of technetium-99m (Tc-99m).

Its proposal builds on research by the Idaho National Laboratory and a suggestion made by Ottawa-based Mevex.

Scientists at the NRC Institute for National Measurement Standards (NRC-INMS) have already tested every step of the linear accelerator method. The research partners expect it could ultimately make enough isotopes to supply all of Canada’s requirements.

According to Dr. Carl Ross, who leads the NRC-INMS team, the new method does not pose any security or nuclear proliferation concerns because, unlike a nuclear reactor, it requires no weapons-grade uranium. What is more, it generates virtually no radioactive waste materials that must be stored indefinitely. “Using a linear accelerator, you essentially produce only the isotope that you want, so there is negligible waste,” he said.

“The linear accelerator method is virtually guaranteed to replace the nuclear-reactor production method,” added Dr. Ross. “The physics are well established. The chemistry of separation is well known. So I don’t really see any impediment to it being successful.”

In the new method, a high-energy linear accelerator bombards coin-sized discs of the stable isotope molybdenum-100 with X-rays to produce radioactive Mo-99. Mo-99, with a half-life of 66 hours, soon decays into the desired Tc-99m. Tc-99m can then be separated from Mo-99 using technology developed by U.S.-based Northstar Medical Radioisotopes.

Over the next two years, NRC will work with its collaborators to develop a manufacturing process. A demonstration facility will be constructed at the Canadian Light Source in Saskatoon to prove that a high-power electron accelerator can produce a significant fraction of the medical isotopes required by nuclear pharmacies across the country.