Medical officials in Ottawa say that they're being careful with their use of medical isotopes because of a shortage as two of the world's nuclear reactors are shut down for maintenance.

The reactor in Chalk River, Ont., about 180 kilometres northwest of Ottawa, was shut down in mid-May because of a small leak of the heavy water used in the nuclear reaction process.

And next week, a reactor in South Africa will also be shut down for maintenance, leaving only one reactor in the Netherlands to fuel the world's supply of medical isotopes.

Medical isotopes are used in diagnostic imaging to detect diseases such as cancer and heart disease.

The Chalk River reactor produces one-third of the world's radioactive materials.

Alan Thibeau, manager of nuclear medicine at the Ottawa Hospital, said hospital staff have been working hard to ration the isotopes they do have.

"Up to now, we have slightly reduced the total amount of radioactivity that we're injecting in each of our patients to conserve radioactivity," he said.

Waiting period 'very difficult'

Thibeau said he had almost cancelled 70 per cent of his diagnostic tests because of the shortage, but got a last-minute call from his suppliers to say they had found more isotopes to get him through the next few days.

"We have no way of really knowing what the next two or three weeks will mean for us, since I'm only given information about our supplies at the end of a week for the upcoming week," said Thibeau.

Francoise Turcotte, director of nuclear medicine at the Gatineau hospital, said she's had to cancel bone and cardiac tests for the next two weeks.

Patients whose cancer has already been diagnosed won't be affected by this shortage yet, she said, but people who still don't know if they have cancer will have to wait.

Ottawa-area cancer survivor Dianne Hartling said that for many, that period of uncertainty is the most difficult.

"That waiting period of not knowing is very difficult for patients. Your cancer is not going to wait. It's going to continue spreading and you want to treat it as soon as possible," said Hartling, who helps run a support network for women with breast cancer.