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Radiology

Questions raised about X-ray emissions and safety

X-ray-induced cancers kill as many as 2,500 Canadians a year, according to an internal Health Canada document that was provided to the CanWest News Service. The Health Canada analysis estimates that even a 5% reduction in radiation dose “would translate in the saving of 125 lives per year.”

Nearly three million Canadians will have a CT scan of their brain, lungs, joints, stomachs or other organs this year. Tens of thousands more will have an angioplasty or other X-ray-guided procedure to prop open clogged coronary arteries, shrink uterine fibroids and diagnose stomach ulcers and other illnesses.

“In general, these procedures are of benefit to Canadians since they allow a shorter stay in hospital and reduce the need for surgery. However, the risks of cancer and deterministic effects [injuries] are not negligible,” according to the Health Canada document, obtained by Ottawa researcher Ken Rubin.

Some abdominal CT scans expose people to 250 times the radiation of an ordinary X-ray. A single chest CT can deliver a radiation dose to the breast – one of the most radiosensitive tissues in the body – roughly equivalent to 10 to 25 mammograms, or 100 to 400 chest X-rays.

Researchers recently reported that chest X-rays may double or triple the risk of breast cancer in women genetically predisposed to the disease. The risk was highest in women who had five or more X-rays and in women exposed before age 20.

The use of CT scans for concussions has doubled or tripled over the past 10 years in large Canadian hospitals, and scans of the head and pelvis in children are also increasing rapidly.

The National Academy of Sciences estimates one in 1,000 people who receive 10 millisieverts of medical radiation exposure – roughly the equivalent of one CT scan of the chest or abdomen – will develop a solid tumour or leukemia.

But patients receive minimal information about CT scans, says Dr. Richard Semelka, professor and vice-chair of research in the University of North Carolina’s department of radiology. “They undergo a CT, but nobody says to them that there is a small but definite risk you could get cancer. And I think that is wrong.”

Writing last month in the British medical journal Lancet, Dr. Semelka and co-author Diego Martin say radiation cancer may take five to 20 years to develop.

Radiologists use as little radiation as necessary to get an answer to a clinical question, says Michael Bronskill, a professor in the department of medical biophysics at the University of Toronto.

But doses during interventional procedures can vary substantially, based on the procedure.

“A regular diagnostic angiogram exposed patients to about 2.5 to five millisieverts of radiation,” said Dr. Benjamin Chow, a cardiologist at the University of Ottawa Heart Institute. For angioplasties, it could be an extra 2.5 millisieverts, or as high as 20 millisieverts, during one procedure.

Experts such as Prof. Bronskill say concerns about radiation need to be put into perspective.

“We’re all exposed to ionizing radiation,” he said. The Earth is slightly radioactive. “The average dose to citizens of Canada from medical procedures is, I believe, lower than average background radiation.”

Dr. Semelka says hospitals should keep permanent records as a way to track how much radiation people are exposed to from CT scans and X-ray-guided procedures and to consider alternative tests, such as ultrasounds or MRIs, where appropriate.

“What I don’t want the public to come away with is the concept that CT is terrible. It’s not. It’s a terrific modality. It’s very fast, it’s very accurate,” Dr. Semelka said.

“The risk is small, but think twice about getting the second one. Think three times about getting the third.”

 

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