Medical isotopes: What are the alternatives?
Atomic Energy of Canada (AECL) officials said on Aug. 12, 2009, that Ontario's Chalk River nuclear reactor will not be able to restart producing medical isotopes until the spring of 2010, at the earliest.
A spokesman for AECL said by early January 2010, only 24 per cent of the work had been completed. But — despite the pace — things are progressing well.
"It's coming along and we are on target to start the reactor near the end of March," Dale Coffin said.
The 52-year-old reactor was shut down in May of last year after officials discovered radioactive water leaking inside it. AECL says that nine sites at the reactor are in need of repair and the list of concerns includes wall thinning and localized pitting that suggests different corrosion effects.
The world's other main isotope-producing nuclear reactor — in Petten, Netherlands — is scheduled to be taken offline for repairs in February — for the second time in a year. The shutdown is expected to last until August.
In February, an isotope supplier announced that the Institute of Atomic Energy in Poland will increase the worldwide supply of medical isotopes at its Maria Reseach Reactor. The plan still needs regulatory approval in Canada and the U.S., and will only produce five to 10 per cent of the world's needs.
With Chalk River's reopening delayed, some medical officials are wondering when the all clear will really come.
"It's analogous to your sitting at the airport and hearing that your plane's delayed three hours, and then four hours — and then next, it's cancelled," said Dr. Kevin Tracey of the Ontario Association of Nuclear Medicine.
Chalk River produces about a third of the world's supply of medical isotopes, handling most of North America's demand. Petten produces a little more than 30 per cent of the world's supply.
So, where could isotopes come from? While both facilities are down, reactors in South Africa, Belgium and France will be hard-pressed to meet worldwide demand.
The prospect of a limited isotope supply has medical officials worried.
"We want to see some action by the federal and provincial governments to assist in really getting ready for what could be an extremely critical time," Tracey said.
Medical isotopes can be the most effective — and cheapest — tools in diagnosing cancers such as breast, lung and prostate cancer. The detailed information they provide — what's happening at the cellular level — helps patients and health-care providers determine the most effective way to treat an illness.
Technetium-99 is the most widely used isotope for diagnostic imaging. It accounts for as many as 20 million diagnostic nuclear medical procedures every year. It is used for getting a detailed look at the heart, kidneys, lungs, liver, spleen and bones as well as for blood-flow studies through single-photon emission computerized tomography (SPECT) scans.
Forty per cent of technetium-99 is used for cardiac purposes. Another 40 per cent is used for cancer assessment. The remaining 20 per cent is used for everything else.
There are alternatives for some of the tests. Not all are ideal, and not all are readily available.
Turning to older technology
When the isotope supply is low, a CT, or computerized tomography, scan may be an option. A CT scan is similar to an X-ray, except it reveals much more detail.
A CT scan will provide pictures not only of bones and organs but also their inner structure and detailed shots of the pancreas, adrenal glands, kidneys and blood vessels.
It is useful in diagnosing cancer. But it's not for everyone. Some are allergic to the "contrast fluid" patients must either drink or have injected before undergoing a CT scan. The reaction can be severe. Also, CT scans might not be able to detect cancer as early as nuclear medicine scans that use the isotopes that are now in short supply.
It's similar for magnetic resonance imaging, or MRI — a technique that uses a magnetic field and radio waves to create detailed images of organs and tissues. This process creates 3-D images that allow health-care professionals to examine organs, tissues and the skeletal system.
It can be used to diagnose tumours in the lungs, liver, kidneys, spleen, pancreas, uterus, ovaries, prostate and testicles. It can also be used, in addition to mammography, to help detect breast cancer, especially in women who have dense breast tissue.
While the test is non-invasive, people who suffer from claustrophobia can have difficulty with MRIs. Patients have to lie fairly still for up to an hour inside a small, cylindrical chamber.
Like CT scans, MRI images may not be able to detect cancer as early as nuclear medicine scans. After Chalk River went down in 2007, Health Canada and provincial health ministries recommended that in the event of another isotope shortage, where possible, hospitals should switch to thallium 201 for cardiac imaging.
A thallium stress test, in which a small amount of thallium is injected into the patient's bloodstream, is used to detect blocked arteries, causes of chest pain, whether a patient has had a heart attack and the level of exercise a patient can safely perform.
It's a very effective test, and the production of thallium does not rely on a nuclear reactor. The isotope is produced in individual hospitals in cyclotrons, a type of particle accelerator.
But there is a problem: only a limited number of hospitals have access to cyclotrons. So, thallium can be expensive.
The same is true of iodine 123, which is primarily used to generate images of the thyroid. It's also produced in a cyclotron, so it's expensive and can be difficult for some hospitals to acquire.
SPECT scans rely on isotopes produced in nuclear reactors. Dr. O'Brien says positron emission tomography (PET) scans are a good alternative — except they're not widely available in Canada, and they're expensive. They use isotopes produced by cyclotrons — not aging nuclear reactors.
Thomas Ruth, a research scientist at the Vancouver-based TRI-University Meson Facility (or TRIUMF), Canada's national particle and nuclear physics lab, says he believes the future lies with PET, "primarily because PET has better resolution and sensitivity in human scanning."
But widespread use of PET scans is still a few years away since the necessary infrastructure is not yet in place, he said. Currently, only a few dozen hospitals — and a few private clinics — across the country have PET scanners.
"If we could use PET, there is a network of cyclotrons developing that could cover approximately 75 per cent of the Canadian population," Ruth said. "This network is still months to a bit more than a year away."
Ruth noted that the isotopes PET scanners rely on have even shorter half-lives than the isotopes SPECT scanners use, so each PET scanner should be located close to a cyclotron.
At the end of May, the federal government announced it was setting up an expert panel to study other ways to produce isotopes.
"We would like to have seen something sooner," O'Brien said. "We are happy it's here finally, but at the same time, we've lost a year and a half getting things organized."
The Canadian affiliate of International Physicians for the Prevention of Nuclear War says there's another reason to get away from isotopes produced at reactors like the one at Chalk River. The reactor uses highly enriched uranium to produce the molybdenum-99 that is used to produce medical isotopes.
It's the only grade of uranium from which it is possible to produce a plutonium bomb directly.