OTTAWA - Natural Resources Minister Lisa Raitt isn't making any promises to hospitals that they'll get all the isotopes they need.

Raitt told MPs Tuesday it's hard to promise something that's in such short supply these days.

"There's going to be a shortage of supply of medical isotopes. And as such you can't promise something that you simply don't have," she said.

Raitt said there's no need to panic because Canada is negotiating with other isotope-producing countries to get alternative supplies and hospitals are performing different diagnostic tests that don't need isotopes.

The federal and Ontario governments have advised doctors to time procedures so patients who need higher doses of radiation go first, to work evenings and weekends before the isotopes decay, to use fewer isotopes but run tests longer, and prioritize scans so urgent tests are done first.

Raitt also refused to characterize the shortfall as a "life and death" situation like other Conservatives - including Prime Minister Stephen Harper - did when the Chalk River reactor was shut down in late 2007.

Not that opposition MPs didn't try to goad her into saying so.

New Democrat MP Nathan Cullen asked why the situation was so dire last time - when all five of the world's isotope-producing reactors were running - while this time only one reactor is running and no one knows how long Chalk River will be shut down.

"How I characterize or don't characterize a situation is not as important as how I deal with a situation," Raitt retorted.

Crown-owned Atomic Energy of Canada shut down the aging reactor May 15 after finding a heavy-water leak.

Officials say the reactor - which supplies a third of the global supply of isotopes used in cancer and heart scans - will be off-line for at least three months.