Reactor Shutdown Causes Delays In Medical Tests

A troubled Canadian nuclear reactor is causing delays in molecular imaging for thousands of patients who rely on the scans to guide life-saving diagnoses and therapies. Ontario's 50-year-old Chalk River reactor is the source of about half of North America's supply of molybdenum-99, a key component in nuclear medicine for patients with cancer, heart disease, and bone fractures.

The Toronto Star reports that the reactor was shut down for four days in mid-November for a routine monthly inspection, when reactor staff noticed that an emergency power supply was not connectedâ''a task that was supposed to have been completed two years ago.

According to the Canadian Society of Nuclear Medicine, about 400 000 patients in the United States and 30 000 patients in Canada receive such tests each week. â''Nuclear medicine services are now being rationed across Canada,â'' says the society. The Canadian Broadcast Corp. quotes a nuclear medicine specialist in Halifax, Novia Scotia, who says he has been canceling 100 tests a week.

The repairs are expected to extend into January 2008, and the Star reports that the reactorâ''s owner, Atomic Energy of Canada Limited, does not have all the parts necessary to perform the emergency upgrades. The fixes involve connecting pumps that circulate heavy water to a back-up power supply. In the event of a major earthquake, this measure would prevent the reactor from overheatingâ''an important step in safeguarding the facility from a core meltdown.

Radioactive isotopes have three main uses in medicine, the most common of which is diagnostic imaging. This branch of medicine uses radioactive tracers that emit gamma rays within the body, which are detected by a system and used to build up an image of, for example, an organ. A common source of such a tracer is molybdenum-99, a product of uranium fission. It has a half-life of 66 hours, which means that it cannot be stockpiled and must be shipped daily to hospitals across the continent. Molybdenum-99 decays into the isotope technetium-99, which is the end product that is used as an imaging agent in 80 percent of all nuclear medicine. It has a half-life of 6 hours.

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