Doctors are looking for alternatives to maximize the supply of medical isotopes. (CBC)

As the supply of medical isotopes dwindles across Canada, specialists in nuclear medicine expressed concerns Wednesday that patients' appointments to undergo diagnostic scans may be cancelled.

"As we go further into this week, we're very concerned that we're going to have to turn patients away, look for alternate sites for them to be imaged," said Kevin Tracey, medical director of nuclear medicine at Hôtel-Dieu Grace Hospital in Windsor.

The concern is for some patients with life-threatening pulmonary embolisms — blockages in the arteries of the lung — who urgently need lung scans with isotopes because they are allergic to the contrast dye used in CT scans, the normal way of diagnosing the condition, Tracey said.

Without proper diagnosis, a patient without the disease may be improperly treated with a blood thinner, which could put them at long-term risk of bleeding complications. Occasionally, patients may have extensive clots in their lungs that were unexpected and could go untreated, with risk of sudden death.

"These kinds of situations are what I fear the most," Tracey said.

"As we go into the periods where the isotope is not available, these are the urgent and emergent scans that won't get done as isotope supply dwindles further."

The shortage of medical isotopes was caused by a shutdown last month of the nuclear reactor at Chalk River, Ont., which normally produces the bulk of the world's supply. It's expected to be out of service for months.

So far, some non-critical tests have been shifted or deferred, and all patients needing critical tests have received them, according to the Ontario Association of Nuclear Medicine.

Cancellation fears

Hospitals are concentrating activity to maximize supplies, said Tracey, who also oversees nuclear medicine at the Leamington District Memorial Hospital in Leamington, Ont.

Tracey said he sees "great pessimism in the medical community" over medium- or long-term solutions, given that a Dutch reactor — the second-largest supplier of the molybdenum-99 isotope used in imaging tests after the nuclear plant in Chalk River — will be down for a month in the middle of July, and will go offline again for six months in January.

Some hospitals have said they will not have any supply of medical isotopes by the end of the week, while others will have from 10 per cent to 70 per cent of their supply, said Dr. Jean-Luc Urbain, president of the Canadian Association of Nuclear Medicine.

"It's starting to look very bleak," Urbain said, noting that daytime appointments have not yet been cancelled.

Doctors have turned to older, alternative isotopes such as thallium-99 for heart scans, but the supply of thallium is also insufficient, Dr. Christopher O'Brien of the Ontario Association of Nuclear Medicine said Tuesday.

"We have to use 20th-century tools to practise medicine in 2009," Urbain said. "I'm afraid we're going to start hearing [of] more and more cancellations."