How much cancer risk is there in getting a CAT scan?By- Dr. Joan PellegriniThis is a very difficult question to answer. However, there is a growing concern about what that answer may be because of the extensive use of x-rays in medicine. There is a growing concern that the increasing use of radiologic studies may lead to an increase in our cancer rates. Plain x-rays do not use much radiation but CT scans use much more. Since the 1980’s there has been a rapid rise in the use of CT (Computed Tomography) scanning in the medical field. CT scans use a form of radiation in order to produce images. Doctors order CT scans frequently in order to give us information to aid in diagnosis or to prepare for a surgical procedure. A CT scan can tell a medical professional about what an organ or tissue may look like without actually performing surgery to look. There are obvious benefits to using x-rays and CT scans. Unfortunately, there is also a risk because of the exposure to radiation. The Radiological Society of North America (www.radiologyinfo.org) publishes information on how much radiation exposure happens with various x-ray studies.To put the amount of radiation it in perspective, the average American is exposed to about 3 mSv (a mSv is a measure of a type of radiation) per year of background radiation (basically everything around us is at least a little bit radioactive). Most of our exposure comes from the radon in our homes. In contrast, a CT scan of the stomach exposes a patient to 10 mSv (about 3 years’ worth of ambient exposure). A chest x-ray only exposes us to 0.1 mSv (about 1/100th that of a CT scan). Cell phones have hit the news lately because of the accusation that extended use may cause brain cancer. Cell phones, power lines, computers, microwaves, etc emit a non-ionizing radiation which is less damaging than the ionizing radiation of x-rays because it does not penetrate the skin and cells as easily. Therefore, one cannot easily compare this type of equipment and radiation with medical imaging radiation.Another concern is airport x-ray machines. For the most part, these are used on the luggage and not on the passengers. The new total body scanners do use radiation that amounts to approximately 0.001 mSv (1/1000th of a chest xray). The type of radiation is called “backscatter” and is weak and bounces off the skin. It is not strong enough to penetrate tissues and therefore is no more risky than sun exposure. TSA states on their website that this amount of radiation is equivalent to two minutes of flying on a jet. Metal detectors use a magnet and no radiation. So, from the numbers above, it becomes clear that CT scanning exposes a patient to a significant amount of ionizing radiation. We know that too much ionizing radiation will increase a patient’s risk of developing cancer. What we don’t know is how much is too much and how increased is the risk? Some experts would contend we are seeing increasing rates of cancer in patients who frequently undergo CT scanning. Although this is debatable, I would suggest that caution be used. CT scans should only be ordered if there is likelihood that it will yield useful information and if that information will be used by a medical professional to tailor treatment. In other words, a CT scan should not be done just to see if it shows anything. This is an important concept because many patients and physicians have the mistaken belief that it won’t hurt to order a CT scan and see if it shows anything wrong. One CT scan is probably not worth worrying about. However, it may be concerning if someone has several CT scans over several years. A classic example would be a patient who gets a CT scan every year or two to look for a kidney stone, evaluate for appendicitis, or look for a cause of abdominal pain.The current recommendation from radiologists is that a patient and medical provider discuss why the imaging study is being ordered and what information is expected to be obtained. Also to be discussed is what other diagnostic modalities are available and how will treatment change based on the radiology results. A patient should understand the concept of accumulating radiation exposure and accumulating risk.