A Toronto-area widow was shocked to receive a letter from Trillium Health Services this week informing her late husband that there may have been a problem with the interpretation of his CT scan.

Grace, who did not want her last name published, lost her husband to stomach cancer in February. Eight months earlier, a radiologist told him that he was cancer-free.

The letter addressed to Grace’s husband is one of 3,500 notices being mailed out to patients who have had scans and mammograms done at two Trillium hospitals – Mississauga Hospital and Queensway Health Centre – between April 2012 and March 2013.

Patients with questions or concerns are urged to call Trillium's dedicated access line at: 905-848-7534

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Trillium Health said it’s reviewing tests interpreted by a veteran radiologist with “performance issues,” Dr. Ivo Slezic.

Slezic, who had worked at Trillium hospitals for 33 years, is no longer employed there.

Grace said receiving the letter about her husband’s scan was “upsetting.”

“First of all, it's addressed to my husband like he's still alive when he's not," she told CTV Toronto.

Had her husband been properly assessed last June, "I think maybe he would have lasted a little bit longer, maybe the treatment would have been different,” Grace said.

“I don't know.”

After Trillium Health made the review of Slezic’s work public on Wednesday, other patients have come forward with their stories.

One young woman said she was given a clean bill of health after a CT scan in March, only to find out later that a tumour had developed into Stage 4 cancer.

Another man who went to the hospital with chest pains was told that he had a simple inflammation of the airways. A different doctor later diagnosed him with lung cancer.

Jackie Manthorne of the Canadian Cancer Survivor Network said her organization has been hearing from “patients and ordinary members of the general public who are concerned that they can't trust their results.

"Once their tests results come back read erroneously, by the time the error is found some people will have with these cancers that were missed, will have gone on to develop advanced cancer,” she said.

Manthorne also questioned why it took so long for Trillium Health to notify patients of potential errors. Concerns about the radiologist’s work were first raised in March.

“The system may have worked eventually, but…from our point of view it’s not working quickly enough,” she said.

Manthorne’s group is calling for more training, more supervision and regular testing of radiologists.

In British Columbia, radiology tests are routinely reviewed for accuracy and Alberta is preparing to launch a similar program next year.

The Ontario Association of Radiologists has said that errors are rare in diagnostic radiology.

Ontario Premier Kathleen Wynne said that a review will make sure there are no systemic issues.

Dr. Brian Yemen, chief of diagnostic imaging at Juravinski Hospital and Cancer Centre and McMaster University Medical Centre, is leading the review of the potentially problematic scans and mammograms. The review will involve 16 to 17 radiologists.

With a report from CTV Toronto's Austin Delaney and CTV's medical specialist Avis Favaro