In 2009, the unexpected shutdown of the Chalk River nuclear reactor in Ontario, Canada meant that the global medical community was suffering from shortages of a critical diagnostic tool — radioactive isotopes used by clinicians to diagnose everything from heart attacks to thyroid cancer. Then doctors found out the situation would go from bad to worse. An aging nuclear reactor in the Dutch town of Petten, source of a third of the world’s supply of the most important medical isotope, Technetium 99m, was going off line in February for critical maintenance.
Until summer of last year, the world’s doctors watched waiting lists for diagnostic procedures grow, and in some cases did without otherwise routine medical tests, because the two reactors that each produce a third of the world’s supply of medically important radioactive isotopes were both off-line. It was an outage for which no one was prepared.
Isotopes 101
To understand why the outage was so critical, it helps to know a little about medical isotopes. More than 80 percent of all radioactive isotopes are Technetium 99m, which is spontaneously produced from Molybdenum-99 in a process called radioactive decay. Moly 99 is in turn typically produced inside a nuclear reactor by fission of highly-enriched Uranium 235.
After the Moly 99 is siphoned off, it can be transported to regional hospitals and pharmacies, where its half life of about a week means that it is continually producing Technetium-99m, which is then chemically attached to biologically active molecules. When the combination of Technetium and those molecules is injected into a patient, it accumulates in tissues that are making use of the biologically active portion of the compound. As a result, low levels of radioactive material accumulate in areas of the body that are of interest, for example, the heart, lungs or bone, and this radioactivity can be visualized with a SPECT (single photon emission computed tomography) camera.
The resulting images can provide clinicians with more detailed views than imaging technologies such as x-ray or MR alone, providing insights that can help clinicians detect disease earlier and more precisely monitor treatment..
Shutdown in 2016
At present, both the Dutch and Canadian reactors are operational again, and doctors have enough isotopes to carry out millions of routine nuclear medicine procedures per year, as they have in the past. But because both of these reactors, as well as all of the rest in the small fleet of research reactors that generate medical isotopes, are rapidly aging, a replacement for them is desperately needed.
The Canadian government has even given the world a hard deadline for this replacement. In 2016, it has pledged to shut down the 50-year-old Chalk River reactor forever.
“It’s not clear if they will follow through on that, because there could be enormous pressure to have the reactor stay on longer,” says Tom Ruth, an expert in nuclear medicine and a nuclear chemist at Canada’s TRIUMF subatomic physics laboratory. Ruth is heading one effort to find a way to produce medical isotopes that doesn’t rely on 60′s-era nuclear reactors fueled with weapons-grade Uranium-235.
Ruth and his team are working on a way to produce Technetium 99m with the same cyclotrons that are currently used to produce radioactive isotopes for PET scans, which are more detailed than SPECT scans but also significantly more expensive. One advantage of this method is that there are already many PET cyclotrons in the world, though not nearly enough to completely replace supplies of isotopes from nuclear reactors.
Another alternative is to bombard Moly-100 with high powered rays of light. This method is complicated and has yet to be demonstrated as a working system, says Ruth. Meanwhile, GE Hitachi Nuclear (GEH) is trying to make it possible to produce isotopes from the kind of nuclear reactors that are presently only used to generate power. (GEH is a global nuclear provider alliance created by GE and Hitachi; GE is the sponsor of this magazine.) Finally, the Dutch have pledged to build a replacement for their aging reactor, though it won’t come on line until long after the 2016 deadline.
Abandon isotopes?
The solution to the problem of shortages of Technetium 99m may be to simply abandon it, says Ruth. While the SPECT scans it enables are widespread, there is an alternative, PET, though it’s more expensive. The possibility of a transition to PET is one reason Ruth’s solution involves repurposing cyclotrons that will some day be useful for PET scans.
“I see it as a stopgap, because you can’t go from all SPECT to all PET overnight,” says Ruth. In Canada, where he is based, there are over a thousand SPECT scanners, and replacing them with PET scanners would cost $2 million each.
No matter what combination of solutions the world relies on for resolving future shortages of medical isotopes, the result will almost certainly be increased costs for already-overburdened medical systems. That makes resolving this issue as much a question of politics as nuclear physics.
Top image: The Chalk River Laboratories.
Christopher Mims is a contributor to Good, Technology Review and The Huffington Post, and is a former editor at Scientific American and Grist.org. His last article for Txchnologist looked at delays to the technology behind air traffic control. He tweets @mims.