Can we trust imaging scans? High-levels of radiation could cause cancer Tom Blackwell, National Post Published: Friday, April 11, 2008 They are among the wonders of modern medicine: Machines that peer deep inside the human body and capture pictures of striking and invaluable clarity. It is not surprising that the number of Canadians who receive computed tomography (CT) scans, MRIs and other diagnostic imaging tests -- often with life-saving results -- has exploded in recent years. But as the numbers soar, experts are increasingly concerned that, for some patients, CT scans are actually doing more harm than good. Delivering radiation doses far greater than conventional X-rays, CT tests sow the seeds of hundreds of cancer deaths a year in Canada, by some estimates. At the same time, patients are sometimes getting the tests when they do not need them. Lack of knowledge among non-radiologist doctors, pressure from patients and a generally over-burdened system mean that as many as a third of CT scans are prescribed unnecessarily, some experts argue. "Quite often the physician, they're ignorant of what test to order for the patient's condition, and end up ordering every test under the sun, just to cover their butts," says Craig Wilson, president of the Ontario Association of Medical Radiation Technologists. For the first time, the Canadian Association of Radiologists' annual scientific meeting next month will be devoted almost entirely to addressing such radiation safety issues. CT scanning is now virtually unregulated in Canada, although studies have shown different hospitals can deliver widely divergent radiation doses from the machines. A report commissioned by the Ontario government urged almost two years ago that the province set up a new oversight system for the technology, a recommendation later echoed by the provincial auditor-general. The government has yet to act on the proposal, while other provinces have done even less. Experts stress that CT scans play a crucial role in medicine; the benefit easily outweighs the risk for most people who receive them. But specialists say that some patients simply do not need the scans, and could receive a lower dose of radiation or undergo a different, safer type of imaging. "Physicians who are not radiologists, whether they be GPs or emergency docs or whoever, need to be a little more aware - a lot more aware - of radiation exposure of their patients," said Dr. David Vickar, president of the Canadian Association of Radiologists. About 2.7 million CT exams were administered in 2004-05, up 8% from the year before, according to the Canadian Institute for Health Information. A study at a major B.C. hospital found the number of CT tests had more than tripled between 1991 and 2002. Dr. Richard Semelka, a Canadian radiologist who teaches at the University of North Carolina and has been outspoken about the risks of CT scans, said that with statistics ballooning, now is the time to act on radiation concerns. "I'm hoping ... we'll all be thinking much more carefully when we order CTs so we don't see 10, 15, 20 years down the road this bulge of new cancers that come from our aggressive, halcyon use of CT studies," he said. "[But] I'm afraid it might be litigation that forces change." CT scanners are dazzling tools. The machines rotate a thin X-ray around the patient's body, then use computers to generate three-dimensional, cross-section images of a body part. They expose the anatomy of organs, bones and blood vessels the way regular X-rays never could, and are the gold standard for diagnosing certain cancers, planning surgeries and finding internal injuries and bleeding in trauma patients. But that clarity comes at a cost. An abdominal CT scan generates 500 times the radiation of a conventional abdominal X-ray. An oft-cited report by the American Academy of Sciences estimates the 10 milliSieverts of radiation from each abdominal CT exam will trigger an extra one cancer case per 1,000 people. A 2004 study concluded that diagnostic radiation overall accounted for one in a hundred cancers in Canada - or 784 cases a year. However, the estimate was based on data from the early 1990s, before the recent surge in CT use. An internal Health Canada document in 2005 suggested that radiation from diagnostic imaging causes 2,500 cancer deaths annually. "If only a 5% dose reduction could be achieved, this would translate in the saving of 125 lives per year," the government report notes. In fact, exposure to CT scans could be limited much more than that if the technology was more properly used, some experts argue. An article last November in the New England Journal of Medicine suggested a third of the scans in the U.S. are not medically justified, meaning 21 million Americans "are being irradiated unnecessarily." Dr. John Mayo, radiation safety chair of the radiologists' association, believes the problem is more modest, but allows that 10% to 20% of the tests done in Canada may be unwarranted. Part of the problem is that physicians, other than those who specialize in radiology, receive little training in medical school about the technique and its uses, says Mr. Wilson, who supervises CT scanning at an Ontario hospital. "They order the wrong test first, where, for example, an ultrasound of the abdomen and pelvis could have been tried," he says. "If they do that and it's positive, they don't have to do the CT. There's a lot of frustration there." As well as analyzing the eventual images, radiologists are supposed to vet requests from other physicians and suggest changes when they receive an inappropriate order. But the growing doctor shortage is leaving them with less time to carry out such screening. More training for the ordering physicians would certainly help, agreed Dr. Mayo, a radiologist at Vancouver General Hospital. He noted that studies have found doctors are often ignorant of the relative radiation doses from CT scans. "General practitioners ... are overwhelmed with the amount of material they have to understand: disease states, pharmacology etc. Then diagnositic imaging comes along and changes every six months," says Dr. Vickar, based in Edmonton. "It becomes more difficult for non-radiologists to figure out what is the best test." When CT scans are done repeatedly, sometimes even the patients complain, said Mr. Wilson, who added that prescribing doctors tend not to welcome his questions about necessity. Radiation levels are important in CT, as the resolution of the pictures increases with the X-ray dose. Though the field has long been dedicated to the principle of using the least amount of radiation necessary, a 2006 study by Dr. Mayo and colleagues found that some hospitals in B.C. employed as much as eight times the dose of radiation in their abdominal CT scans as others. A 2006 report by the Ontario auditor-general noted that half the physicians the office surveyed wrongly used higher, adult doses of radiation in CT scans of children. Young people are a particular concern, since their tissue is more sensitive to radiation damage, and, with more life ahead of them, they are in greater danger of contracting cancer down the road. But if physicians sometimes choose CT scans incorrectly, patients themselves bear part of the blame, experts say. Robin Hesler blames it on television: Just as it seems every patient on the TV shows Grey's Anatomy and House requires a CT or MRI, viewers have begun to demand the same for themselves in real life, says Dr. Hesler, CEO of the Ontario radiation technologists' group. "Some physicians are seeing a number of patients a day who are requesting these things and say, ‘Well, it's just easier to do the test than argue with them,' " Dr. Vickar says. Professional groups like the radiologists' association have developed guidelines on dosage use in CT scans, but no government has made them the standard across any province, let alone the country. By contrast, the European Union adopted guidelines for the whole continent about four years ago. A June, 2006, report called on the Ontario Health Ministry to set up a CT safety committee and develop standards for radiation exposure and testing of scanners. There is little regulation or inspection of the diagnostic tool now, concluded the report, commissioned by the ministry. As another possible solution, Dr. Vickar points to a pilot study at a children's hospital in Winnipeg, where doctors are using a computer program that analyzes information on individual cases, then suggests the best diagnostic imaging technology based on accepted guidelines. Meanwhile, for doctors afraid of missing anything in their diagnosis, the draw of sophisticated imaging like CT scanning remains powerful, says Dr. Mayo. "We believe our eyes so much," he said. "That's why ‘show me' is such an important thing in life. You want to see it." National Post [EMAIL PROTECTED]
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