The risk of radiation posed when you undergo a computed tomography



It is often said: "What you do not know will not hurt you". But I've never understood the reason behind that. In fact, as a doctor, I would say the opposite: that what you do not know can hurt you.

I am thinking about this in light of recent studies on exposure to radiation from medical imaging tests such as computed tomography (CT) scans. Many of us do not know that we are exposed to ionizing radiation when we undergo computed tomography, that ionizing radiation is a carcinogen, or that the data links an increased risk of cancer with low doses that are commonly used in computed tomography images. .

And although that increase in risk may be small, it is also cumulative over time, a concern for patients who receive multiple exams.

The benefits of CT scans to diagnose illnesses and save lives are indisputable. But, like any medical test or treatment, CT scans carry potential risks that must be compared with the expected benefits. Unfortunately, we have paid little attention to radiation risks.

Putting risk in perspective is difficult, taking into account the various criteria by which significant exposure to radiation and cancer risks are measured. But, in general terms, we can consider the constant background radiation of the natural sources to which we are exposed every day. While a chest x-ray exposes us to a 10-day dose of background radiation, a CT scan of the chest offers a value of about 2 years. And the average 3-year dose that we get from a CT scan of the abdomen and pelvis more than doubles when the scan is repeated with and without contrast.

It is important to remember that the highest cancer risk from a single CT scan remains low for most people. Even so, the risk is accumulated with an additional scan, and constitutes an unnecessary risk if the scan is not medically necessary.

According to estimates, this last point deserves to be underlined because about 30 percent of the CT scans done in the USA. UU They are unnecessary. And, given that we perform more than 80 million CT scans per year, it is a surprise to consider the extraordinary unnecessary risk we badume as a population. In fact, taking this perspective of the population, researchers have estimated that almost 2 percent of future cancers could be related to CT scans.

Given the risks, our causal attitude towards CT scans is surprising. But they have become the basic element of Big Mac of modern medicine. As a matter of perceived need or convenience, too many doctors order them and many patients request them when they are not medically necessary.

The reduction of radiation risk could be pursued through several strategies, beyond the obvious one of reducing unnecessary explorations. Another obvious tactic is to minimize the amount of radiation per scan without sacrificing the quality of the image.

I would expect the radiation doses for optimal CT images to be somewhat standardized and applied in a predictable manner, given our concerns about risk and our extensive experience with CT imaging for four decades. But that is not the case.

In fact, it has been known for years that the doses used are very variable, both within and through the institutions. For example, a study in 2009 revealed a 13-fold difference between the lowest and highest radiation doses used for identical CT procedures at four clinical sites within the Bay Area.

Last week, the researchers reported on their efforts to discover what could be responsible for the ongoing variations in CT radiation dosing at 151 institutions. Published online in "The BMJ", they concluded that dose variations were largely due to choices made by individual institutions when setting the technical parameters for CT scanning, not to variables such as size of the patient or bad, or the brand or model of the scanner.

In other words, patients were exposed to multiple variations in radiation dose by the chance of idiosyncratic CT protocols.

The lead author of the study, Dr. Rebecca Smith-Bindman of UC San Francisco, concluded with optimism that, given these findings, "a single set of achievable quality standards for radiation dose should be established and applied in all hospitals and image installations. "

Even so, no organization in the United States is at the proverbial rudder, responsible for collecting or monitoring CT radiation doses. And although California pbaded a law that requires documentation in the patient's medical record of the radiation dose used in each CT scan, compliance has been inconsistent.

We can all help limit exposure to unhealthy radiation from medical images. But to do so, we must be aware of what can be hurting us.

Kate Scannell is a Bay Area physician and the author, most recently, of "Inmortales Heridas."


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