CT Scans May Increase Cancer Risk

Is it really an issue? Recent news reports are based on a new publication in the New England Journal of Medicine. Let’s take a look at that report.

CT scans (also called computed tomography scans) have been in use since the 1970s. The rate of CT use has increased rapidly, from 3 million tests in 1980 to about 62 million a year currently (4 million of these in kids). No wonder, as the test is quick, in most cases it is easy for the patient, and it gives the physician a clear 3 dimensional view inside the body.

The largest increases in use have been seen in the areas of adult screening and pediatric diagnosis. Adult screening has become quite popular, and includes virtual colonoscopy, lung cancer screening for current and former smokers, assessment for cardiac disease, and whole body screening. In kids, the increase is attributed to the fact that the speed of the test (about 1 second) allows it to be performed without sedation. The concern about CT scans is greatest for kids because in theory, kids have a long life ahead, and the more years they have to live, the more time there is for any potential damage to their body (cells) from radiation to show up and cause health problems.

While in most cases, the risks will outweigh the medical benefit, researchers point out that about one-third of the CT scans performed are not medically necessary. In some cases, a test that does not use radiation could be an option (i.e. ultrasound, which uses sound waves or MRI, which uses magnets to produce the image). Perhaps for some, a good old-fashioned medical examination may be an alternative. The researchers feel that some of the unnecessary testing may be due to physicians ordering scans in order to avoid missing anything and cover themselves legally, or due to a lack of communication.

So, is one scan actually dangerous? Let’s take a look at the amount of radiation a particular organ receives with common radiologic studies. An x-ray at the dentist’s office results in the brain receiving 0.005 milligrays (or mGy- the measurement used to describe radiation doses). A routine chest x-ray results in the lung receiving 0.01 mGy, while a mammogram gives 3 mGy to the breast. An abdominal CT scan gives the stomach 10 mGy. In a baby, the exposure level is 20 mGy- 100-200 times the amount of radiation received with a typical x-ray.

But there is more. One study reported that almost all patients undergoing a CT of the abdomen or pelvis had more than one scan taken. Perhaps it was because the film quality was not good enough or the person moved during the scan, but whatever the reason, this results in multiple doses of radiation.

How do they know this dose can result in cancer? Using the long-term follow up of people exposed to atomic bombs in Japan in 1945, researchers can extrapolate the risk of cancer after a certain amount of radiation exposure. Many of these survivors were exposed to a similar amount of radiation (although to the whole body), and an increased risk of cancer has been seen in this group.

What does this mean for the individual? Studies like this one are not easily applied to an individual, as the research is evaluating trends in an entire population, and so there is no need to panic. The risks to any one individual who has a few tests done over in a lifetime are very minimal. That being said, a bit of common sense could go a long way. This study has made physicians more aware of the radiation exposure involved in a CT scan, and may encourage some healthy hesitation before doctors jump to order these tests.

As a patient, you are your own advocate. If you see more than one doctor, as many of us do, be the main communicator between them. If you had a CT scan a month ago and another specialist orders one, tell him or her of the test you had and see if that will suffice. Request that the radiology imaging center share your results with all of your physicians. Ask your healthcare provider if another type of test could substitute, or if the CT test is really necessary.

As for people with known or suspected cancer, CT scans provide a wealth of information for both diagnosis and response to treatment. As for people with known or suspected cancer, CT scans provide a wealth of information for both diagnosis and response to treatment. And when needed, the risk far outweighs the benefit, but we must consider how it will change the treatment course. For example, after starting a new chemotherapy regimen, it is typical to wait 3-4 cycles before repeating a CT scan in order to give the tumor a chance to respond. A test done too soon would give us little additional information, and give the patient needless exposure. It can be hard to wait for that next scan, but you can see your team has your overall health in mind.

The American College of Radiology (ACR) has information for both physicians and their patients. They recommend that patients keep a record of their x-ray and CT scan history and talk with their doctor about the rationale for the CT scan, if one is recommended. The ACR also provides accreditation of facilities with x-ray technology and defines criteria for providing the most appropriate imaging scan.

Brebber, DJ & Hall, EJ Computed tomography--an increasing source of radiation exposure. New England Journal of Medicine. 2007 Nov 29; 357(22) 2277-2284.