It has been a decade since the world grappled with the challenge posed by Canada’s aging nuclear reactor, the NRU, which at one point was producing almost half of the global supply of Molybdenum 99, an isotope used in millions of medical scans every year. The reactor was finally retired in 2018, but a concerted effort in the preceding years had created a network of cyclotrons across the country to replace this lost capability and produce isotopes for clinical applications.The creation of this network was a major accomplishment, but it was matched by a parallel initiative to apply a different technology to the same problem. Instead of cyclotrons, which can be expensive and hard to manage, research groups in Saskatoon and Winnipeg examined the prospects of small-scale linear accelerators.
“For the same investment as a cyclotron, you can put in a linac and serve 10 radiopharmacies,” says Mark de Jong, Chief Technology Officer for Canadian Isotope Innovations (CII) Corporation, the Saskatoon-based enterprise that is introducing this technology to potential users with a need for isotopes.
CII is based in the same facility as the Canadian Light Source, the landmark synchrotron that de Jong helped to build and where he led the initial work on medical isotope production with linear accelerators. Although this work did not proceed at the same pace as that with cyclotrons, it is now ready to bring some distinct advantages to this specialized but important market.
“There’s a movement toward electron accelerator production of moly [Mo99] as being the most plausible alternative decision,” he explains. Whereas cyclotrons use molybdenum targets to create technetium99 — the isotope that is actually used in scanners — this product only has a six-hour half-life, which restricts the geographic area that can be served by this method. A linac, on the other hand, produces Mo99 with a 66-hour half-life, so it can be shipped much further before being converted for use at a medical imaging clinic.
Unfortunately, the concentration of Mo99 generated in this way is a tiny fraction of that generated by fission in a nuclear reactor, but the linac is much less hazardous to manage. “From a regulator’s perspective there is no question which would be preferred,” says de Jong, adding that the price differential between the two systems is just as profound.
That advantage provided the incentive to found CII in 2015 and begin working on the problem of how to enhance Mo99 output to meet the needs of the health care community. In the meantime, researchers have identified other isotopes of interest, such as Cu67, which can be used to target cancerous tumours and eliminate them with a short-lived, close-range radioactive probe.
“It turns out that the only clean way of producing it is with an electron linac,” de Jong explains.
In addition, the International Atomic Energy Agency (IAEA) facilitates collaborative research between various member countries, so that they can sample innovations that might be worth adopting. About 15 of these states have expressed interest in linear accelerator medical isotope production, but there are few places that have reached the point of being able to demonstrate this technology and enable others to work with it.
“The size of accelerator that we have fits nicely into the infrastructure of many of those countries, compared with a big research reactor,” he observes.
With IAEA’s help, teams from South Africa and Poland wound up in Saskatoon earlier this year, when CII offered them a rare opportunity to try out this hardware for themselves. Philip Pare, a senior electronic engineer with the South African Nuclear Energy Corporation, braved the dead of winter on the Canadian prairies in order to use CII’s linac to bombard a molybdenum target with photons and measure the yield of a gamma-N reaction that produces Mo99.
“We’ve taken certain reactions that we’ve found in the literature and we’re trying to verify whether the results that other people got maybe 14 years ago can be replicated,” he says. “It’s a wonderful opportunity for us to take a look at this technology.”
Pare adds that medical isotopes are currently produced in South Africa’s 16 MW Safari reactor, but as it approaches the end of its working life in the coming decade, the country is preparing to move to a different platform that will not require such a major investment. De Jong says that Canada could likewise move toward linac technology in much the same way.
“We’re looking at an accelerator facility that would be like a high-end cyclotron lab in terms of cost, but that would make enough Mo99 for all of Canada,” he concludes.