Canada's Chalk River nuclear research reactor is one of the world's main sources of medical isotopes, but is scheduled to be shut down in 2016. Credit: ZUMA Wire Service / Alamy

A Canadian-led team says that it has succeeded in proving the feasibility of using particle accelerators instead of nuclear reactors to produce a badly needed medical isotope. If health regulators approve the method, it will place supplies of the crucial material on a far more secure footing.

“We have found a practical, simple solution,” François Bénard of the British Columbia Cancer Agency in Vancouver, said on 20 February at the annual meeting of the American Association for the Advancement of Science (AAAS) in Vancouver.

“It's using the existing infrastructure in the best possible way,” agrees Karlheinz Langanke, director of the Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, who attended the AAAS presentation but is not involved with the project.

Isotope generation

More than 80% of medical-imaging procedures, including those used to help diagnose cancers or monitor heart function, employ a radioactive tracer called technetium-99m (99mTc), a decay product of molybdenum-99 (99Mo). With half-lives of 6 hours and 66 hours, respectively, neither isotope can be stockpiled but must be continuously generated.

Supplies of 99Mo mainly come from two nuclear-reactor facilities: the National Research Universal reactor in Chalk River, Ontario, Canada, and the High Flux Reactor in Petten, the Netherlands. Both reactors are ageing and have experienced sudden shut-downs in recent years, placing the entire 99mTc supply chain at risk and making headlines world wide.

The Petten reactor is due for replacement in 2015, and the Canadian government has said that the Chalk River facility will close in 2016, so researchers have been looking for a more reliable alternative source of the isotopes. Earlier this month, General Electric, headquartered in Fairfield, Connecticut, announced that it was abandoning a project to convert naturally occurring molybdenum-98 into 99Mo within commercial nuclear-power reactors. The company said that the plan was not cost effective.

Cyclotron route

Now, a team based at the TRIUMF particle accelerator near Vancouver has announced another approach. The idea is not new. For decades researchers have known that 99Mo can be created using an accelerator, but the method was generally thought to be too expensive or impracticable to scale up, potentially requiring newer, higher-power accelerators. “We were told it could be done, but not routinely,” says Bénard. It took the TRIUMF team less than 2 years to overcome the barriers.

The technique uses standard cyclotrons, such as those made by General Electric and already installed in many hospitals. The room-sized machines fire protons at a liquid target to produce other isotopes used in medicine. The TRIUMF team found that for the cost of a few hundred thousand dollars, these cyclotrons could be upgraded and used to bombard a coin-sized solid metal target made of non-radioactive molybdenum-100.

“We give it a bit more oomph,” says Paul Schaffer, head of nuclear medicine at TRIUMF. The trick to making the procedure practical was doing it without needing to open the cyclotron to insert and remove the metal disk, which would expose staff to radiation. The team solved the problem with a mechanical arm. “Think of a plumbing snake,” says Schaffer. Once recovered, the disk is dipped in a chemical bath to release the technetium.

The technique has been demonstrated at two facilities in Canada, producing enough 99mTc to theoretically supply hundreds of patients. Preliminary work shows that the product is equivalent to what comes out of reactors — something that regulators will need to verify before the method is approved.

One potential difficulty with the new system involves transport of the isotopes. Because 99mTc is produced directly, doctors would have only about 12 hours to get the isotope to patients; 99Mo production provides a transport window of days. It would mean that Canada couldn't export the isotopes, as it currently does from Chalk River. “We're talking about a decentralized system for regional production,” says Schaffer.

The group would like to see Health Canada step in and provide funding for hospitals to invest in the needed equipment. It is unclear whether that will happen, however. Some still hold out hope that the Chalk River facility will be extended again beyond 2016, but Schaffer thinks that unlikely. “I've heard from the government that they're done with this.”

the hand shows the target apparatus. Credit: TRIUMF