They're the backbone of nuclear medicine. Medical isotopes — tiny radioactive particles that can be injected into the body — have become the standard treatment for some cancers. They've also brought medical imaging to new levels.

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A sign warns of possible radiation outside the nuclear reactor at the Atomic Energy Canada Ltd. plant in Chalk River, Ont.

And much of the world's supply is produced in Canada.

The National Research Universal (NRU) reactor went fully online at Chalk River, Ont., on Nov. 3, 1957. It has been used for scientific research, including the development of nuclear medicine. It remains the biggest single source in the world of the isotope cobalt-60, which has been used in cancer treatment for more than half a century.

Chalk River's importance gained worldwide attention in 2007 when the reactor was shut down for maintenance, causing a worldwide shortage of medical isotopes. And it was underscored again in August 2008 when the other four major producers of isotopes — reactors in the Netherlands, Belgium, France and South Africa — all scheduled maintenance and refuelling stops within weeks of each other.

Reactors in all five countries are at least 40 years old — and showing their age.

Atomic Energy of Canada Ltd. was forced to close the NRU reactor again on May 14, 2009, after the power went out in parts of eastern Ontario and western Quebec. The next day, officials detected a heavy-water leak at the base of the reactor vessel in a place where there is corrosion.

AECL initially said repairs would take a month, then three. But on Aug. 12, 2009, AECL officials announced the NRU reactor would not be able to start producing medical isotopes until at least the following spring.

On July 7, 2010, the Canadian Nuclear Safety Commission said the reactor was ready to resume production again. It authorized Atomic Energy of Canada Limited to reload fuel into the reactor.

The prolonged shutdown led to a shortage of the isotopes used in medical imaging — it also led to spikes in the price of isotopes.

Canadian doctors expressed their concern about what they called the "prolonged" shortage of medical isotopes. At the annual meeting of the Canadian Medical Association in Saskatoon in August 2009, they passed a resolution calling on the federal government to conduct "open, meaningful and ongoing consultations" with the nuclear-medicine profession on the issue.

At its annual meeting in Salt Lake City, Utah on June 8, 2010, the U.S.-based Society of Nuclear Medicine chastized Ottawa for the ongoing isotope shortage and called on the American government to ensure that enough isotopes could be produced in the U.S. so the medical profession would not have to rely on foreign producers.

International isotope suppliers and distributors have turned to reactors in Poland as well as in Russia to expand their sources.

What's being done to address shortages of medical isotopes?

The International Atomic Energy Agency (IAEA) says the world is facing the risk of a supply problem as the demand for radioactive materials used in medicine continues to grow, and the reactors that produce them continue to age.

When it's operating, the Chalk River reactor produces enough isotopes to treat more than 76,000 people a day — more than 20 million a year.

Almost half the reactors worldwide are between 40 and 49 years old. Only 14 per cent of them are under 20 years old. The agency notes that no new isotope production facilities have been commissioned for years.

In November 2008, the IAEA released a collection of recommended practices, which was drafted to help the operators of research reactors run their facilities safely and reliably.

In February 2009, the agency brought together representatives of 16 countries to try to come up with strategies to address challenges to the reliable supply of technetium-99. The isotope is used in medical tests as a radioactive tracer that medical equipment can detect in the body.

While the participants were resigned to the likelihood of increased shortages of medical isotopes in the short-term, they did come up with recommendations aimed at minimizing supply disruptions. Among them, reactor owners and operators:

  • Need to share information and better co-ordinate reactor maintenance schedules. 
  • Should be encouraged to find ways to increase production from existing reactors in times of global shortage.

Are new facilities in the works to meet demand?

The IAEA says while improvements to some existing facilities around the world are in the works, no new plants have been commissioned for years. The agency notes that it would take years to get from the construction phase to isotope production at any reactor currently on the drawing board.

The National Research Universal reactor at Chalk River was scheduled to be decommissioned in 2005 and be replaced by two new reactors called Maple 1 and Maple 2. Those reactors were initially supposed to be completed in the early years of this decade and be dedicated solely to the production of medical isotopes.

But in May 2008, the AECL scrapped the plan because of continuing problems with the reactors, putting more pressure on NRU to continue to supply the bulk of the isotopes.

There are other reactors that can produce medical isotopes in Canada. For instance, McMaster University in Hamilton, Ont., has operated a small reactor for 48 years. It's capable of producing a few medical isotopes including iodine-125, but not enough to pick up the slack caused by the extended shutdown of the NRU reactor.

On November 30, 2009, the Expert Review Panel on Medical Isotope Production established by Natural Resources Canada released its report. It called for less reliance on Chalk River by diversying into other sources of medical isotopes.

The four other main reactors in the world producing medical isotopes are the BR-2 reactor at the Belgian Nuclear Research Centre, the Osiris reactor in France, South African operator Nesca's Safari-1 reactor and the High Flux Reactor at Petten in the Netherlands. These four and NRU combined to produce 85 per cent of the world's supply of cobalt-60 and almost all of the molybdenum-99 and technetium-99. They're all over 40 years old.

How are medical isotopes useful in diagnosing illness?

Put simply, medical isotopes give off energy that can be detected by imaging equipment. When isotopes are injected into your body, a doctor can — for example — get a clear picture of how your heart is working. The doctor can see whether you're a heart attack waiting to happen. They'll see enough to know whether you should go straight to the hospital for bypass surgery.

The isotopes provide far more information than an ultrasound. They make bone scans far more effective than X-rays. In a bone scan, radioactive material is injected into a vein in the arm. The material travels through the bloodstream and eventually settles in the bones. This will give doctors information on cell activity from which they can tell if you have stress factures in your feet or whether the cancer in another part of your body has spread to the bones. Bone scans can detect problems days or even months before X-rays.

How are medical isotopes used in cancer treatment?

Modern radiation therapy was pioneered in Canada in 1951 in hospitals in Ontario and Saskatchewan. Cobalt-60 was used in a treatment that allowed medical technicians to target a specific part of the body.

The energy given off by medical isotopes is effective at destroying diseased cells. When cancer cells are targeted and destroyed, healthy tissue is left alone.

Are there different types of medical isotope treatments?

Besides standard radiation therapy, there are three common types of treatment using medical isotopes.

Brachytherapy is a form of radiation therapy where radioactive isotopes in the form of small pellets (called seeds) are inserted into cancerous tumours to destroy cancer cells while reducing the exposure of healthy tissue to radiation. It is currently approved for treatment of prostate cancer and cancers of the head and neck. There are also studies underway to see whether it can be used in the treatment of lung cancer.

In radioimmunotherapy (RIT), doctors inject antibodies that have isotopes attached. The antibodies (called monoclonal antibodies) flow through the bloodstream and deliver the radioactivity by seeking out and latching onto proteins on the cancerous cells. Again, it allows doctors to spare healthy tissue while targeting diseased cells. RIT is being studied in several cancers, but has shown the most promise in the treatment of blood cell cancers, such as leukemia and lymphoma. It is also being looked at for treatment of prostate, colorectal and pancreatic cancers, and soft tissue sarcomas.

Medical isotopes can also be paired with carriers that are attracted to certain parts of the body. For instance, chemical phosphonates are naturally attracted to the bone.

Delivering medical isotopes to the bone by attaching them to phosphonates is now being used to treat pain associated with cancer that has spread to the bone. As well, iodine has been used for thyroid treatment for years because it is naturally attracted to the thyroid. The medical isotope iodine-131 is used to treat thyroid cancer.

What are some of the challenges in using medical isotopes?

One of the key problems is that many isotopes lose their radioactivity very quickly so they cannot be stockpiled. Cobalt-60 has a half-life of 5.26 years. However, molybdenum-99 has a half-life of 66 hours, which means it loses half its radioactivity in just less than three days — and half of what's left in another three days. That's critical because molybdenum-99 is used to produce technetium-99, which is used for eight out of every 10 nuclear medicine procedures.

Iodine-131 has a half-life of 8.02 days while iodine-125 loses half its radioactivity every 59.4 days.

The short half-lives of key isotopes means they have to be delivered quickly.