More than 60 million CT scans are performed every year in the United States. A CT scan uses a computer to assemble multiple x-rays taken in rapid sequence to produce a far more detailed image than a conventional x-ray. CT scans are helpful in the diagnosis and management of many medical conditions.
All tests have a risk-benefit ratio. With a CT scan it is important to balance the information the test may or may not yield and how that information might affect the management of your medical condition against the risk of the test. And CT scans have risk. Radiation from x-rays damages DNA, which can cause cancer and for women the radiation can also damage the ovaries. So many CT scans are performed every year in the US it is estimated they cause 1% of cancers in this country. While some doctors argue that estimate is too high, there is no denying that radiation has risks, and whether CT scans cause 0.4% of cancers or 2% of cancers is not really the point. The safest level of radiation is the lowest level of radiation.
The risk of cancer from a CT scan depends on age and the body part scanned; children and young women are at greatest risk. The breasts are especially vulnerable, so a CT scan to the chest carries the greatest risk. The risk of cancer for a women in her 20’s from a chest CT may be as high as 1%. The risk of cancer after a CT scan of the abdomen for a woman in her early 20’s is 1/1000.
Women also have the added risk of radiation damage to the ovaries, potentially affecting fertility. While you can’t shield your ovaries during a scan of your belly, make sure you are given a lead apron to place over your lower belly to protect your ovaries when any other part of your body is x-rayed. It is also important to not be pregnant during a CT scan as high levels of radiation may have consequences for the baby. If you are not using highly reliable contraception and are sexually active, you could be pregnant.
If you are critically ill a CT scan is a powerful tool that may help determine the type of urgent or emergent care that you need. CT scans identify bleeding and infection in the belly, blood clots in the lungs, and bleeding into the brain. There is no doubt CT scans are life saving for thousands of people, and in these situations the benefits far outweighs the risks. CT scans are also very useful for evaluating response of certain cancers to chemotherapy and helping to plan specific surgeries.
However, in evaluating a chronic symptom the benefit of a CT scan should be highly scrutinized. Some experts believe up to 1/3 of CT scans might not be justified (Brenner and Hall, NEJM; 2007). The reason behind all these extra tests isn’t really known, but it is probably a combination of factors: fear of missing something, medico-legal concerns, failure to realize another test without radiation could be used, and patient reassurance. It has also been suggested that doctors who have ownership in the center where the CT scan is performed (or the equipment) are more likely to order a scan.
So if you are sitting in your doctors office talking about a pain you have had for a long time and a CT scan is recommended, think about asking these four questions
- What are you specifically looking to find and how will those results affect my treatment? If there is not going to be any effect on treatment, then the test is probably not indicated. Also, if your doctor can’t tell you what they want to find or exclude then you should ask for another option or another doctor. Considering the risks of radiation, it’s hard to justify a fishing trip.
- How much radiation does this scan deliver? In my opinion, if an ordering provider doesn’t know that answer, they shouldn’t order the test. Doctor’s should know the benefits AND risks of every test they order.
- Is a test without radiation, such as an ultrasound or an MRI, an option?
- Do you have any ownership in the center where you have referred me for the scan?