More than 80 million CT scans are done in the U.S. each year to help diagnose many medical conditions. In 2007, the National Cancer Institute predicted that 29,000 future cancer cases could be linked to the CT scans performed in the U.S. in that year alone, and doctors have ordered more CT scans every year since then. CT scans of the belly and pelvis are associated with increased risk for blood cancers over the next two years (JAMA Surg, 2021 Apr 1;156(4):343-351). A study of 825,820 people who had an appendectomy for acute appendicitis found that 306,727 had had a CT scan before their appendectomy while 519,093 did not have a CT scan. In the next two years, those who had had a CT scan were 26 percent more likely to develop a blood cancer, most commonly leukemia. Other studies come to the same conclusion: CT scans were associated with elevated risk of thyroid cancer and leukemia (NCI Cancer Spectrum, Feb 2020;4(1):pkz072); and a study of 12,068,821 people found significantly increased risk for cancer in those who had CT scans (JAMA Netw Open, 2019;2(9):e1910584).

What is a CT Scan?
A CT scan (Computed Tomography) uses multiple X-ray measurements taken from various angles to produce an accurate cross-sectional image of parts of the body. It does not require placing anything inside of your body and can be used in patients with pacemakers or metal implants.

CT scans can be used to visualize every organ in the body, and can help to diagnose heart, lung, muscle and bone diseases. CT scans have been used frequently during the COVID-19 pandemic, because the virus can cause clots, and CT scans can find clots to guide treatment with anti-clotting agents.

CT Scans Emit Far More Radiation than Routine X-rays
A single CT scan emits 200 to 300 times the amount of radiation that comes from a single chest X-ray (Am J of Roentgen, Aug 2001;177(2)). Radiation can damage the DNA genetic material in cells, kill some cells, and cause increased expression of genes involved in the repair or death of cells (J Amer Coll Cardiol, July 22, 2015).

Normal cells live only a limited time and then die. This is called apoptosis. For example, normal skin cells live 28 days and then die; cells lining your lips live 24-48 hours and then die; red blood cells live 120 days and then die. When radiation damages DNA, normal cells can forget to die and become cancerous.

Your immunity is supposed to search out and destroy these abnormal cells that do not die, but sometimes they continue to grow (as in a tumor), and may spread to other parts of your body. A localized cancer such as breast cancer does not kill as long as it is just in the breast, but breast cancer cells can travel to your brain, bones, liver, lungs and so forth, where they destroy essential functions and kill you.

The risk for cancer increases linearly with the dose of radiation. A CT scan of your internal organs can emit doses that are up to 500 times those of a single conventional X ray (0.01 to 0.15 mGy compared to 80-100 mGy for certain CT scans).

My Recommendations
Radiation damage is cumulative over your lifetime, and some treatments of diseases or trauma can require a lot of radiation exposure. CT scans are more of a concern than single X-rays because they emit so much more radiation. If your doctor recommends a CT scan, ask if there is an effective alternative with less radiation. Sonograms use sound waves which are harmless. MRIs do not produce radiation, but they are often not used because they are more expensive than CT scans, and they usually cannot be used on people with pacemakers or some types of metal implants.