End of an era

A global shortage of medical isotopes used for diagnostic imaging could occur later this year when Canada stops production next month. The looming shortfall of molybdenum-99 (Mo-99) and technetium-99m (Tc-99m) has prompted discussions between the US government and global suppliers to ensure that supply meets demand until other sources of isotopes come on stream.

Canadian Nuclear Laboratories (CNL) is the Canadian supplier of Mo-99 and it plans to cease production in October. It becomes a supplier of last resort in case of severe shortages until the aging National Research Universal (NRU) reactor in Chalk River ON is shut down for good March/18.

The global supply chain is examined in a new congressionally mandated report by a special committee of the US National Academies of Sciences, Engineering and Medicine (NAS). It was tasked with building a sustainable national isotope strategy, assessing the short-term supply of Mo-99 and reporting on progress on phasing out the use of weapons-grade, highly enriched uranium (HEU) — the fuel source used by the NRU to produce Mo-99.

The report notes that Canada has yet to "publically describe the supply shortage triggers that would lead it to order a restart of Mo-99 production at NRU during the contingency period". It's estimated that isotopes are used in 35 million medical procedures annually, with growth coming primarily from rapidly expanding Asian nations.

"Before 2010, the NRU supplied more than 40% of the world market. With the shutdown of 2009, AECL (Atomic Energy of Canada Ltd, the NRU operator prior to CNL) lost a lot of customers," says Dr Thomas Ruth, an emeritus senior research scientist at TRIUMF, emeritus senior scientist at the British Columbia Cancer Research Centre and vice-chair of the NAS Committee on the State of Molybdenum-99 Production and Utilization and Progress Toward Eliminating Use of Highly Enriched Uranium (HEU). "Canada now provides only 29% of the world supply but it still has that larger capacity. As of October 31, 2016, that reserve capacity goes away."

Ruth says the world's four other processors are reliant on old reactors and "barely meet the demand" for Mo-99. If a problem occurs requiring reactor shutdown — there have been at least eight in the past six years — "there's a substantial probability of a shortage between now and 2018".

A long and complex journey

Canada's decision to exit the medical isotope business is long and complex, but most agree that the expensive failure of AECL to develop its MAPLE reactors for isotope production was the tipping point that compelled the federal government to explore alternative sources.

An extended shutdown of the NRU exacerbated the situation and the government responded by providing $25 million in seed funding for several projects using cyclotrons and linear accelerators (R$, March 14/13). Four projects are now scheduled to come on-line over the next three years (see chart).

"In Canada, cyclotron technology is more advanced, it's local and it's green," says Ruth. "You need many machines to meet need. In Canada it's about 10 cyclotrons while the US estimates that it needs at least 100."

Isotopes without the use of HEU

The US Department of Energy is also supporting a new class of reactors capable of producing medical isotopes without using HEU, providing up to $25 million in matching funds for the peer-reviewed development and demonstration of new technologies. Under development are low specific activity reactors from GE/Hitachi, Babcock & Wilcox Enterprises and NorthStar Medical Radioisotopes LLC.

The report's mandate includes recommendations on how to shift away from weapons-grade HEU — an initiative that has been underway since 1999 as part of the government's nuclear non-proliferation policy. AECL's MAPLE reactor development program (in conjunction with MDS Nordion) explored the use of LEU but it was abandoned as too expensive.

Canada has agreed to take its HEU out of circulation and has already begun repatriating the material to the US as part of a US-Canada agreement signed in 2010.

"Canada will ship HEU to the US and store it in the Savannah River, returning it to where it came from," says Ruth. "The report recaps what has happened in the past five years with the removal of HEU."

Loss for research community

For the research community, the loss of the 59-year-old NRU — a hybrid HEU-powered reactor used by government, academic and industry — marks the first time in decades researchers won't have access to a domestic nuclear reactor. The Canadian Neutron Beam Centre has been used by hundreds of scientists annually, even as its management was shuttled between AECL and the National Research Council.

Ruth says that Canadian scientists will now have to negotiate access to foreign reactors.

"They'll have to do their research elsewhere. It's difficult but feasible. The NRU represented an enormous resource for the field. It's absence will be missed but hopefully not be felt too much in the long term," he says. "It's an unfortunate situation that has come about but it's primarily a political situation."

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