Questions raised about X-ray emissions
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
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
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.”