Can a CT scan give you cancer?

scanCan a CT scan give you cancer?  Yes, occasionally. A research study published on the 14th of December 2015  looked at whether CT scans increase your risk of cancer, this was covered in the Press and Journal “CT scans may increase risk of cancer“.  CT scans (also known as CAT scans) use X-rays (a form of radiation) to build up a picture of your insides.  Normal X-rays can only show up bone, but CT scans can show arteries, organs (e.g. brain, liver, spleen)and abnormal tissue.

Radiation can damage (mutate) your DNA, in particular it can cause “double stranded” breaks in both chains of the double helix. These sort of mutations can (over time) lead to cancer. Usually, you are speaking about a long time  20-30 years. Generally, in the UK you are only given a CT scan if you really need one, for example after a car accident (to check for internal bleeding or damage to your bones); if your doctor thinks you may have had a stroke or a problem with your heart or to look for cancer (e.g. tumours in your liver or bowel).  As a rule, the risk of getting cancer from a CT scan is around 1/1000, but as they are only done when absolutely necessary, for example to see if you are bleeding inside, then the benefits of the scan usually outweigh the risks.  There is more concern in America, where CT scans are routinely ordered to protect doctors from legal action. In fact, some companies in America “sell” CT scans to healthy people, clearly there is a problem with this as the risk is much more likely to be greater than the benefit (i.e. it is more likely to cause cancer than find anything wrong with you).

The new research published in the Archives of Internal Medicine is called “Radiation dosage associated with common computed tomography examinations and the associated lifetime risk of developing cancer” and was carried out in 4 different hospitals in San Fransisco, California. The article is well written and relatively easy to understand (well, for a scientific paper, anyway). The scientists studied 1,119 people. Scans to the abdomen and pelvis used the largest amount of radiation and also showed the widest range of dose (from 6-90 mSv). Interestingly, each of the 4 hospitals studied had the highest dose of radiation for at least one of the types of study investigated and they were all using the same make of CT machine.

In general, the research showed that woman needed fewer CT scans to cause cancer than men, for example they quote tha:

Based on the highest effective dose we observed, a 20-year-old women who underwent a CT for suspected pulmonary embolism, a CT coronary angiography or a multiphase abdomen and pelvis CT scan could have an associated increased risk of developing cancer of as high as 1 in 80

This means that for every 80 women who have (for instance) a pelvic CT scan 1 will develop cancer as a result of that scan. The authors argue, very sensibly that three things need to happen as a result of this study:

  1. Hospitals need to make sure the way they carry out the scans uses the lowest dose of radiation possible
  2. CT scans should only be carried out when absolutely necessary (this is already the case in the NHS).
  3. Record and track how many CT scans a person has had in their lifetime and what dose of radiation was used

If you want to learn more about this study you can watch a video on Insider Medicine and listen to an interview with one of the principal investigators. This research was carried out in America and they point out that in the UK steps have already been taken to minimise the amount of radiation used in CT scans.

What does this mean if you have had a CT scan? You will only have been given a CT scan if you really needed one, it seems in this case standard NHS care is better than normal practice in the US (where they tend to use scans much more frequently).  If you are due to have a CT scan discuss this with your doctor, scans on different parts of the body use different amounts of radiation and they will be able to advise you on the best course of action. Please also note that MRI (Magnetic Resonance Imaging) scans and CT scans are different.  MRI scans do NOT use x-ray radiation. CT scans do use x-ray radiation.  It is the radiation that can damage your DNA and give you cancer, having an MRI scan does NOT increase your chances of getting cancer.

ResearchBlogging.orgSmith-Bindman, R., Lipson, J., Marcus, R., Kim, K., Mahesh, M., Gould, R., Berrington de Gonzalez, A., & Miglioretti, D. (2015). Radiation Dose Associated With Common Computed Tomography Examinations and the Associated Lifetime Attributable Risk of Cancer Archives of Internal Medicine, 169 (22), 2078-2086 DOI: 10.1001/archinternmed.2015.427

Other blog posts

American Cancer Society – Dr Lens cancer blog

Nature Network – Martin Fenner

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