by Dr. C.H. Weaver M.D. updated 7/2021​

Diagnostic imaging can help accurately diagnose disease and contribute to effective treatment planning, but repeated exposure to radiation can increase risk of developing cancer.

X-rays and CT (computed tomography) scans may play an important role in diagnosis of cancer and other diseases and conditions as well as treatment planning. These diagnostic imaging techniques are painless and non-invasive and can create detailed images of the body in seconds. Both X-ray and CT scan, however, use radiation to produce images, and because exposure to radiation is a known cause of cancer, people who are exposed to large or repeated doses of radiation through diagnostic imaging may have an increased risk of developing cancer.

Concerns about cancer risks associated with diagnostic imaging are increasing as use of imaging, particularly CT scans, is becoming more frequent and widespread. CT scans deliver a higher dose of radiation than standard X-rays—doses may be 50 to 500 times higher. And because exposure to radiation adds up over a lifetime, people who undergo repeated CT scans are likely at a greater risk of developing cancer. Risk is also affected by other factors, including the area of body exposed and the patient’s age, with children being more sensitive.

How much may radiation exposure affect cancer risk?

Studies have indicated that 1.5% to 2% of cancers in the United States may be caused by radiation exposure.

How can risk be reduced?

Radiation exposure and associated cancer risks add up over a lifetime, making it important to use CT scans, as well as X-rays, only when there is a valid medical reason. This means that patients who are healthy and at low risk should not undergo excessive CT scans. As well, patients whose treatment plan is not likely to be changed by the results of a CT scan may want to avoid optional testing. In other words, it’s very important that patients and physicians carefully balance the benefits and risks when deciding whether or not to use a CT scan.

It’s also recommended that other diagnostic technologies be considered in order to reduce use of CT scans. Ultrasound and MRI (magnetic resonance imaging), for example, do not expose the body to radiation and may therefore be considered as alternatives to CT scans and X-rays.

Radiation exposure can also be reduced by adjusting radiation doses so that they are appropriate for the patient’s size. This is especially important in children.

CT scan is short for computerized tomography scan. CT scans are a type of X-ray that provide highly detailed images. CT, or CAT scans, are special X-ray tests that produce cross-sectional images of the body x-rays and a computer. CT scans are also referred to as computerized axial tomography.

CT scan images allow the doctor to look at the inside of the body just as one would look at the inside of a loaf of bread by slicing it. This type of special X-ray, in a sense, takes "pictures" of slices of the body so doctors can look right at the area of interest. CT scans are frequently used to evaluate the brain, neck, spine, chest, abdomen, pelvis, and sinuses.

CT is a commonly performed procedure. Scanners are found not only in hospital X-ray departments, but also in outpatient offices.

Questions to ask your doctor before a CT scan

What do you expect to learn from the CT scan and will it change the plan? In “other words” is it truly necessary?

Is a CT scan the best way to learn more about the condition being evaluated? Is there a lower-risk or better option, such as an MRI, PET scan or ultrasound?

Do CT scans cause cancer?

CT imaging exposes patients to higher levels of radiation than any other type of diagnostic radiology procedure. The ionizing radiation emitted from CT scans can harm DNA and cause tumors.

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Children are particularly susceptible to the potential adverse effects of radiation however the diagnostic information obtained by CT is often essential for treatment planning – the risk associated with the CT is worth the benefit, in most cases.

In addition, children’s rapidly dividing cells are vulnerable to radiation from any kind of X-ray. To make CT scans safer, providers use X-ray shields to protect sensitive areas and adjust doses to minimize the risk for younger patients.

Radiation is more dangerous if it takes place on the same part of the body several times and with very high doses. So, radiation doesn’t tend to accumulate if you have multiple CT scans on five different parts of your body.

What is the evidence?

CT Imaging in Kids Raises Cancer Risk

According to one Dutch study published by Dr. Michael Hauptmann, MD, of the Netherlands Cancer Institute in Amsterdam, and colleagues in the Journal of the National Cancer Institute pediatric patients who had CT scans have a higher-than-expected risk of developing cancer later in life.

Researchers at British National Health Service hospitals also reported a link between CT scans of the head and the development of subsequent cancers. They found a clear relationship between increase in cumulative dose of radiation and increase in cancer risk.

Their results indicated that children and young adults who received a cumulative absorbed dose to the head of 50 to 60 mGy had triple the risk of brain tumors and those who received the same dose to the bone marrow had triple the risk of leukemia. As a point of reference—using current scan settings, two or three CT scans of the head would yield a dose of 50 to 60 mGy to the brain and five to ten CT scans of the head would yield that same dose to the bone marrow in children under age 15.2

In the current report Dr. Hauptmann's group analyzed data from the Dutch Pediatric CT Study, which focuses on brain cancer and leukemia but also tracks other cancers. The analysis comprised 168,394 patients who were <18 years when they had CT scans (unrelated to cancer) between 1979 and 2012

The risk for developing any type of cancer was 47% higher and ranged from 11% to more than three times higher for specific types of cancer.

The authors offered a cautious interpretation of the findings, noting that "CT scans for children represent a potentially life-saving and quality of life-improving technique for many patients. In addition, the tumors evaluated here are associated with small absolute excess risks.

The risk is quite small and the benefits of CT scans typically outweigh the risks. CT scans can be useful diagnostic tools; however, it’s important to justify their use and strive to keep radiation doses as low as possible.

References:

  1. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. The Lancet, Early online publication: June 7, 2012. Available at: doi:10.1016/S0140-6736(12)60815-0