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A radiologist examines breast X-rays after a regular cancer prevention medical check-up at a radiology centre in this file photo from November 5, 2012.ERIC GAILLARD/Reuters

Were you one of the patients notified by Trillium Health of possible errors in your CT scan or mammogram? Please e-mail health reporter David Andreatta at or call him at 416-585-5130 to tell your story.

The cited "performance issues" of a radiologist that prompted Trillium Health Partners to review 3,500 mammogram and CT scans for possible errors were related to discrepancies in interpreting the results of the scans, the hospital's chief of staff said Thursday.

Dante Morra said the radiologist, Ivo Slezic, had worked in Trillium hospitals for 33 years and that his interpretations of scans were called into question by the head of the radiology department during a routine quality assurance check of Dr. Slezic's work.

Dr. Morra stressed that the quality assurance check was not prompted by a complaint or by any unorthodox behaviour exhibited by Dr. Slezic. He added that the checks are done annually at the hospital and that none had ever raised doubts about Dr. Slevic's ability to read scans.

Doubts about Dr. Slevic's work were first raised by the head radiologist on March 28, Dr. Morra said, and Dr. Slevic was immediately restricted from reading scans pending a performance review from the hospital's board. The board rescinded Dr. Slevic's privileges to read scans on May 30, and he has since resigned, Dr. Morra said.

The hospital has since hired an outside radiologist, Brian Yemen, the chief of diagnostic imaging at Juravinski Hospital and Cancer Centre and McMaster University Medical Centre, to assemble a team of 15 to 20 radiologists to review Dr. Slevic's interpretation of 3,500 scans conducted between April 1, 2012 to March 31, 2013 at Mississauga Hospital and Queensway Hospital.

Dr. Morra said as part of that review Dr. Yemen would determine whether to expand to scans read by Dr. Slevic prior to April 1, 2012.

"It's impossible to speculate as to when performance issues moved forward," Dr. Morra said. "The key thing is this was caught proactively."

Attempts by The Globe to reach Dr. Slevic have thus far been unsuccessful.

Trillium said patients and doctors whose scans are involved in the review are being notified, and will be followed up with directly after their tests have been checked.

"We apologize for any concern the news of this review may cause and want our patients and community to know it is being done to ensure the highest quality of care at our hospital," Trillium president and CEO Michelle DiEmanuele said Wednesday night in a release.

Phone lines have been set up for patients and doctors concerned about the review of the scans.

"Delivering high quality care and patient safety is our top priority," Dr. Morra said in a release.

Earlier this year, it was revealed that about 1,200 cancer patients in Ontario and New Brunswick had received watered-down treatments, some for as long as a year.

An expert report prepared for the Ontario government called on Health Canada to regulate the preparation of all drug mixtures outside licensed pharmacies.

The report by Dr. Jake Thiessen also urged Ontario to bring in stronger rules for licensed pharmacies.

And in 2011, a Windsor, Ont., surgeon who performed two unnecessary mastectomies was cautioned by Ontario's medical regulatory college.

Dr. Barbara Heartwell became the subject of several investigations after it was revealed she mistakenly removed the healthy breasts of two women at Hotel-Dieu Grace Hospital.

A provincial report into pathology errors largely cleared Heartwell, but uncovered "significant concerns" with pathologist Dr. Olive Williams' work.

After reviewing more than 6,000 reports stretching back to 2003, investigators had moderate or major disagreements with the original diagnosis in 221 of the cases by Williams.

With a report from The Canadian Press