Cancer from X-rays kills hundreds a year

X-ray-induced cancers kill 780 to 2,500 Canadians a year and many new procedures that use X-rays to guide thin tubes and other devices into blood vessels and arteries have not been tested for radiation safety, Health Canada says.

And as the use of ionizing radiation in medicine grows, so do concerns that patients are not being told of rare but potential hazards.

An internal Health Canada document provided to CanWest News Service estimates that even a five-per-cent 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.

Interventional radiology allows doctors to do through tiny incisions what once required major surgery. People recover sooner, with less risk of infection and death.

In almost all cases, the benefit to patients far outweighs the potential risk of a downstream cancer, experts say, but as the procedures become more common, and more complex, concerns about excessive radiation exposure are increasing.

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

"With the increased complexity of these procedures, the irradiation time has also increased, giving rise to concern about patient doses."

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

Last week, researchers 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 or who were exposed before age 20.

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

The International Atomic Energy Agency says radiation doses could be reduced by half or more without jeopardizing safety or image quality.

The National Academy of Sciences estimates that one in 1,000 people who receive 10 millisieverts of medical radiation exposure -- roughly equal to 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 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, Semelka and co-author Diego Martin say radiation cancer may take five to 20 years to develop.

"That really explains why nothing really is told to patients, because people consider it so far in the future," Semelka said in an interview. "It's not like surgery. ... We're talking about something that may be 20 years down the road."

That may not be of concern to older people who may have only a decade or two of life left, but the risks are higher for children and young adults, Semelka says.

Every year in Canada, about 600,000 adults with a concussion are seen in emergency rooms. Eighty per cent were sent to radiology for a CT scan in 2002; in 1997, just 30 per cent were scanned.

The tests are ordered to detect blood clots in the brain, which are rare in patients who are "wide awake and talking," says Dr. Ian Stiell, professor and chair of emergency medicine at the University of Ottawa. Still, they can happen, and they can be disastrous.

The tendency has been to order a CT scan for every minor head injury, even though Stiell and his colleagues have determined only a third to half of concussion patients need one.

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," says 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.

Health Canada is also concerned about dental X-rays, although the radiation doses are substantially lower. Christian Lavoie, chief of Health Canada's medical X-ray and mammography division, says the dose from one dental X-ray is equivalent to a few hours of flying, and that there are "not that many cancer-sensitive organs" close to the teeth.

"Why do we care if it's that small of a dose? The reason is it's probably the single most numerous type of X-ray you could get."

It also comprises the largest number of X-rays given to children. "About 50 per cent of my calls are from parents who are concerned about dental X-rays."

The Canadian Dental Association says the number of dental X-rays should be kept to a minimum, and should be based on a clear medical need.

Chow says the small, one-in-1,000 risk of cancer in patients exposed to 10 millisieverts of radiation, needs to be put in perspective.

"Twenty-five per cent of the population will get cancer -- one in four. So you're increasing their risk of cancer from 25 per cent to 25.001 per cent," he says. "From a medical perspective, we don't think this is a significant increase in risk."

The risks of stroke, heart attack and death during angiography "are actually higher than the cancer risk, and they're also more significant. As physicians, we quote what we believe are the most significant and most relevant risks."

But Lavoie of Health Canada says the risk-benefit needs to be weighed as the procedures grow.

"We do uterine artery embolization (for fibroids), which means a woman doesn't have to have her uterus removed, but we're then putting a whole lot of radiation around the ovaries. Will it mean that we're going to actually create cancer in those women in 10 years?"

The U.S. Food and Drug Administration has passed regulations that will require all fluoroscopy equipment sold in the U.S. to be fitted with displays that monitor X-ray time and track the radiation dose to patients in real-time.

But Semelka says hospitals should also develop permanent patient 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 an MRI, where appropriate.

"First of all, the general public has the right to know. It may then also be beholden on them that they keep track of their radiation and going into emergency, maybe even having a card showing this is what I've had done before."

Adds Semelka: "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.

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

© The Edmonton Journal 2006