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Wrong Radiation Dose Given to Skin Cancer Patients

April 24, 2008

Hundreds of skin cancer patients in Ottawa were given lower-than-prescribed doses of radiation over three years because a hospital employee incorrectly calibrated the radiotherapy unit.

An Ottawa Hospital official said 326 patients who were treated at the hospital's Civic Campus between November 2004 and November 2007 for basal cell and squamous cell cancers were affected.

The two skin cancers, unlike melanoma, rarely metastasize and are primarily the result of overexposure to the sun. None of the patients is believed to have died as a result of the reduced therapy, Chris Carruthers, the hospital's chief of staff, said in an interview yesterday.

"These are skin cancers which are less serious, less aggressive, usually grow over a slow time- so that's fortunate." Dr. Carruthers said.

The error wasn't discovered until last November, when a physicist, as part of an annual inspection of all the hospital's radiation units, decided to do a more thorough review of the machine. None of the hospital's other units was affected, Dr. Carruthers said, and the employee responsible for the error has since retired for an unrelated reason.

The hospital says it immediately began an investigation to determine the scope of the underdosing and later hired a Toronto expert medical reviewer to determine the clinical impact.

In all, 640 patients received 1,000 radiation treatments from the machine. The Toronto expert determined 296 patients were underdosed, 30 fewer than the hospital's own investigation concluded. The underdosages ranged from 3% below the recommended amount of radiation to a few as low as 17% below. The normally accepted variation in dosage is 5% to 7%.

During treatment, radiation energy is directed at the cancerous tissue to damage and destroy genetic material in the cancer cells, which triggers cell death.

Cancer Care Ontario, which has been given the Toronto expert's report, has been asked by the Ottawa Hospital to independently review what happened and make recommendations to prevent it from happening again.