OTTAWA - Smaller hospitals across the country will run out of medical isotopes this week, leaving many cancer and heart patients scrambling to find alternatives.

That sobering news came Tuesday amid demands that Natural Resources Minister Lisa Raitt resign for calling the isotope shortage a "sexy" issue that could boost her political career.

The head of the Ontario Association of Nuclear Medicine said smaller hospitals have been told they won't receive expected isotope shipments.

"There is a marked reduction in availability of medical isotopes this Thursday and Friday, where the shipments that we were hoping would be coming in from South Africa and the Netherlands will not be arriving," Dr. Christopher O'Brien said.

"For some of our smaller hospitals, there will be absolutely no medical isotope availability Thursday and Friday of this week."

O'Brien said that means some patients booked on those days for diagnostic scans to detect cancer and heart ailments may have to be rescheduled.

Uncertainty about hospitals getting their isotopes over the weekend and into next week has left doctors and patients in limbo, he added.

"This will be across Canada and it'll be a patchwork effect as well," O'Brien said.

"Some centres will be a little better off than others. We tend to see the rural centres are the ones that are impacted significantly moreso than the urban centres that can pool their medical isotopes more effectively based on the geography that they're in."

The shortage is due to the emergency shutdown of Canada's aging nuclear research reactor at Chalk River, Ont., which produces a third of the world's medical isotopes.

The latest crisis comes as Raitt is being buffeted by indiscrete comments caught on tape. In a tape of a private conversation between Raitt and an aide, the minister calls the isotope issue "sexy."

The head of the Canadian Association of Nuclear Medicine took exception to that.

"The chronic and acute shortage of medical isotopes is neither a funny nor sexy story," Jean-Luc Urbain said.

"It is a real drama that we have to live with our patients on a daily basis."

He added it's unclear if doctors will be able to do tests later this week.

Raitt has refused to resign -- or even apologize for her comments. She also fended off calls for her resignation last week after the same aide left sensitive government documents about Atomic Energy of Canada Ltd. at a television studio.

An extended isotope shortage could further scorch Raitt.

She said progress has been made in global discussions to pick up the slack left by the Chalk River shutdown and credited "Canadian leadership" for the progress.

She said a reactor in the Netherlands has agreed to increase its supply of medical isotopes by at least 50 per cent, and a South African reactor is also ramping up production.

And, she said, an Australian reactor is now expected to come online "much quicker than they had expected."

But New Democrat MP Nathan Cullen said it's unclear if Canadian clinics will actually get their isotopes.

"The sexy scandal that this minister was hoping for is becoming a true mess because these isotopes will not be here and Canadians are right to be afraid," Cullen said.

Neither Raitt nor Health Minister Leona Aglukkaq were available to comment.

A spokeswoman for Aglukkaq acknowledged there will be supply disruptions.

"Supply will vary -- week by week, shipment by shipment, hospital by hospital, province by province," Josee Bellemare said in an email.

"We know that each health care professional, each hospital, and each province is making maximum use of the available supply of the isotope Technetium-99."

The health minister has touted alternative procedures that don't rely on isotopes -- such as CT scans and MRIs -- as a stopgap for the shortage.

But O'Brien noted that not all patients can undergo those procedures.

"If you have an allergy to the X-ray dye that they use in CT scans, or if your kidneys are not functioning well, or you just can't hold your breath or you're moving a lot for the procedures because you're very ill, you will not be eligible for the CT scan because you're just at too high of a risk," he said.

AECL shut down its 52-year-old reactor May 15 after finding a heavy-water leak. Officials say it will be down for at least three months.