(Symbol image). Computed tomography provides essential cross-sectional images, but works with ionizing radiation. A modeling calculation first organizes how frequently CT scans could contribute to the cancer risk of an entire population in the long term.
(Photo: © Forschung und Wissen)
Computed tomography (CT) is one of the most important diagnostic procedures in modern medicine, saving lives daily. However, a recent model study from the USA brings attention to a rarely discussed downside of this procedure. Researchers estimate how many future cancers could stem from the enormous number of annual CT scans. The calculated magnitude is significantly higher than previous estimates, raising questions about the responsible use of radiation doses in healthcare systems and for individual patients.
CT scans, which utilize X-ray radiation to produce detailed images of the body’s internal structures, uncover injuries, tumors, or bleeding that are often hidden in standard X-ray images. The diagnostic benefits are indisputable, as many treatment decisions in emergency medicine, oncology, and surgery rely on these images. However, each examination exposes the body to ionizing radiation, which is known to potentially trigger cancer by damaging cellular DNA. The radiation dose of a single CT scan often exceeds that of a traditional X-ray by several times. Experts make a strict distinction between the low risk of an individual scan and the cumulative exposure faced by millions undergoing examinations each year. This relationship between individual dose and societal impact is central to new calculations, making this a significant public health issue.
The foundation of this discussion is a statistical model that links known radiation exposures from various procedures with established risk estimates for radiation-induced cancer. Such models are based on data from large cohorts, including studies on survivors of high-dose radiation, and extrapolate the risk to lower dose settings. Thus, the results are not counted cases, but rather predictions over a long timeframe during which radiation-induced tumors could emerge. In radiation medicine, a precautionary principle suggests that every additional dose slightly increases risk, even if exact individual values cannot be measured at low exposure levels. The value of such a calculation lies not in the precise number but in the magnitude it reveals. It demonstrates how a seemingly small risk to an individual can accumulate to a relevant size across a population, thereby advocating for more mindful research on cancer and its preventable causes.
Why the Model Provides High Estimates
A research team led by radiologist Rebecca Smith-Bindman from the University of California, San Francisco, relied on data from an international CT dose registry containing information from over 140 facilities, using a risk assessment tool from the U.S. National Cancer Institute to translate radiation exposure into cancer predictions. For the year 2023, researchers assessed approximately 93 million CT scans performed on about 62 million patients in the United States. This data set led to the estimation that CT scans for that single year could result in about 103,000 additional cancer cases over the lifetimes of the examined patients. This figure is three to four times higher than older estimates, attributed to an increased number of scans and broader data foundations. If current dosage and usage practices continue, CT-induced tumors could account for about five percent of all annual cancer diagnoses, placing this issue in the same realm as alcohol consumption or severe obesity.
Children Particularly Vulnerable, Adults Comprise Majority
A key takeaway involves the unequal risk distribution across age groups. Infants and children face a higher risk per individual examination because their tissues are more sensitive to radiation and they have more years ahead in which a radiation-induced tumor could develop. The calculated risk is highest for children in their first year of life. Nevertheless, researchers expect most projected cancer cases to occur in adults, simply due to this group receiving a vastly greater percentage of all CT scans. Models predict lung cancer, colon cancer, leukemia, and bladder cancer as the more common tumor types in adults, while childhood cancers such as thyroid, lung, and breast cancers are highlighted. Abdomen and pelvic exams account for nearly forty percent of the calculated cases. This breakdown underscores the necessity for radiation protection strategies aimed at both the most sensitive populations and the broader array of examinations to be effective.
Implications for Germany
While the calculations are based on U.S. data, the topic holds immediate relevance for Germany. According to the Federal Office for Radiation Protection, about 130 million X-ray examinations are conducted annually in Germany, with computed tomography accounting for only a small portion. Nonetheless, CT and similar high-dose procedures contribute almost ninety percent to the medical radiation exposure of the population, despite representing only a fraction of all examinations. The average effective dose per individual per year is significantly shaped by these procedures, and their numbers have increased over recent years. Simultaneously, the dose per individual examination has decreased due to technical advances and lowered reference values. Experts emphasize that medically necessary scans should not be avoided due to fear, as their benefits generally far exceed the minimal risks involved. The central message of the study targets unnecessary examinations and excessive doses. Doctors should weigh the necessity of CT scans carefully, avoid medically unwarranted images, and consistently choose the lowest dose that still yields interpretable results.
Published in JAMA Internal Medicine, Projected Lifetime Cancer Risks From Current Computed Tomography Imaging; doi:10.1001/jamainternmed.2025.0505
