Doctors have known that radiation exposure from computed tomography – also called a CT scan – comes with cancer risk. But the risk seems to be higher than previously expected. CT can save lives, but its potential harms are often overlooked.
Researchers analyzed 93 million CT scans done in the United States. They found that the CT scans done in 2023 alone could result in over 100,000 extra cancer cases – around 5 per cent of all new cancers diagnosed every year. The projected number is much higher than previous assessment partly because CT use is 30 per cent higher today than in 2007, according to the study. Lung cancer was projected to be the most common radiation-induced cancer, followed by colon cancer. The researchers highlighted that estimate put CT on par with other significant risk factors, such as alcohol consumption and excess body weight. CT scans use ionizing radiation, which can increase the risk of cancer. However, cancer risk from radiation exposure during a CT scan is quite low
compared to the natural lifetime risk of cancer. Children and teenagers may be especially vulnerable because their bodies are still developing. In adults, cancer risks from low to moderate radiation exposure are largely based on studies of atomic bomb survivors and radiation therapy.
Some evidence suggests that CT can damage DNA. A chest X-ray delivers around 0.1 mSv (millisievert) of radiation, while a CT scan can deliver around 10 mSv, which is 70 to 100 times more radiation in one scan. Exposure to ionising radiation can cause breaks in the DNA strands of cells, which one’s bodily mechanisms may not be able to repair perfectly, leading to mutations that can be passed on when the cells divide. Over time, these mutations can accumulate and cause cells to grow abnormally into a tumour, often leading to cancer. For a single CT scan, the risk is generally low, but cancer risk increases with repeated exposure.
JAMA Internal Medicine, 2025
