Computed tomography (CT) examinations (known more commonly as a “CT scan” or “CAT scan”) incorporate a series of x-ray images taken of areas inside the body and use a computer to create a 3-dimensional (3-D) view. Sometimes doctors inject dye into the patient before the scan, which can help visualize organs or tissues within the body.
While CT scans can help plan a treatment or evaluate how well a treatment works, physicians also use CT scans to diagnose several types of cancer, including colorectal and lung malignancies. Inevitably, patients undergoing a CT scan are exposed to radiation from X-rays. This radiation, known as ionizing radiation , is a type of energy that can cause changes in the cells of the body, potentially leading to cancer. Some basic medical imaging techniques, like an X-ray to diagnose a broken bone or a mammogram, use very low levels of ionizing radiation, but CT scans generate more radiation exposure. Cancer risk can increase from exposure to ionizing radiation used for medical imaging. Still, the risk is generally considered small and outweighed by the benefits of diagnosing and treating a disease.
In the United States, over 93 million routine CT scans occur annually. As a known carcinogen, past research has evaluated the cancer risk linked to CT scans. A 2009 study estimated that 29,000 cancers resulted from routine CT scans performed in 2007, which was about 0.04% of the total number of scans. At that time, experts estimated an annual 70 million CT scans, resulting in a 31% increase over about 15 years. A team of researchers from the University of San Francisco recently set out to determine how the increase in CT scans impacted cancer risk. Their recent report published in JAMA Internal Medicine suggests that radiation exposure from CT scans could have a greater impact on cancer risk than previously believed.
The new study, which evaluated CT scans and organ-specific radiation doses, utilized a comprehensive risk model. The researchers found that approximately 61,510,000 patients underwent the 93 million CT scans performed in 2023. About 96% of these CT scans occurred in adults. The study estimated that 103,000 radiation-induced cancers resulted from CT scans, making the updated risk about 0.11%. These findings provide a detailed and reliable assessment of the cancer risk associated with CT scans.
The study revealed that lung cancer (24,000 cases), leukemia (8,700 cases), and bladder cancer (7,100 cases) had the highest radiation-induced cancer risk. In female patients, breast cancer risk due to CT scans also increased notably (5,700 cases). The researchers linked CT scans to the abdomen and pelvis to 37% of the radiation-induced cancer cases, while CT scans of the chest accounted for about 20% of the cases.
The study demonstrates a significant increase in CT scans and CT-related cancer cases in the United States over the past 15 years. The authors estimate that if the number of CT scans performed in the United States continues to increase at a similar rate, CT-associated cancer could end up accounting for 5% of cancer incidence. These findings underscore the future impact of CT scans on cancer rates, highlighting the need for continued research and careful consideration of the risks and benefits of medical imaging.
Sources: Arch Intern Med, JAMA Intern Med, JAMA