A picture better be worth a thousand words

My friend Michael (a.k.a. this crazy guy – would you please send him to New Zealand?) recently blogged about undergoing what he perceived as an unnecessary medical imaging procedure. He was concerned that this exposure to radiation might impact his fertility. A recent study suggests that Michael should add cancer to his list of concerns.

We’ve known for a long time that radiation is bad news. Scientists studied atomic bomb survivors and found that those who were closest to the blast had a higher incidence of cancer than survivors who were farther from the blast. While the evidence is conclusive, the atomic bomb delivered a much higher dose of radiation than medical imaging procedures. To tease out whether low-dose radiation from medical imaging procedures also increase one’s risk of developing cancer, a team of researchers from McGill University analyzed a group of over 80,000 patients who were admitted to the hospital for a heart attack. They perused the medical records of these patients and noted who received medical procedures involving radiation and who didn’t, and then followed-up by finding out who got cancer later on.

The researchers found that over 10,000 patients developed cancer later on. Interestingly, two-thirds of those cases of cancer were located in the abdomen, pelvis or thorax (presumably the areas that would be subject to medical imaging procedures aimed at the heart). After looking at each patient’s history of procedures, the researchers were able to determine that the more radiation one is exposed to, the higher the risk of developing cancer.

While the study looks at a large number of patients and shows a significant link between radiation exposure and cancer risk, the researchers were limited in that they only had the information available in the medical records. This means that while they controlled for variables like age and sex, they didn’t know everything about the patients: what they ate, how much exercise they did, what kind of environment they worked in. There may be a confounding variable that we don’t know about. As well, the researchers did not assess mortality as an end-point, and even write, “These patients most likely will die of cardiac-related causes”. So it’s important to remember that the scenario is not 1) patient has heart attack, 2) patient undergoes medical procedures, 3) patient gets all better heart-wise but develops cancer because of the procedures, 4) patient dies of cancer. It’s likely much, much more complicated than that.

That said, any medical procedure is all about risks and benefits. We need to weigh the risks of cumulative exposure to radiation (you’ll be glad to know that exposure to radiation from a single test does not substantially increase your risk of cancer) against the value of the information that the medical imaging procedure will provide. Not always an easy task. In Michael’s case, the physician was clear: she was running the test to appease his wife. Now what is that worth to you?

Reference: Cancer risk related to low-dose ionizing radiation from cardiac imaging in patients after acute myocardial infarction. (2011) Eisenberg MJ et al. Canadian Medical Association Journal. [Epub ahead of print].