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Researchers warn that rates are comparable to alcohol consumption, excess weight.
In a nutshell
- CT scans performed in 2023 are projected to cause approximately 103,000 future cancer cases over patients’ lifetimes, potentially accounting for 5% of all annual cancer diagnoses if current practices continue.
- Abdomen and pelvis CT scans contribute most to cancer risk (37% of projected cancers), with lung cancer being the most common projected cancer type (22,400 cases).
- While children face higher risks per scan, adults receive 97% of all CT exams and account for 91% of the projected cancer cases.
SAN FRANCISCO — Millions of Americans undergo CT scans yearly for injuries, diseases, or health monitoring. While these scans are essential medical tools, alarming new research led by scientists at the University of California, San Francisco reveals they might cause about 103,000 future cancer cases from just one year’s worth of scanning in the United States.
If current practices continue, CT-related cancers could eventually make up 5% of all new cancer diagnoses yearly in America, putting CT scans in the same risk category as alcohol consumption (5.4%) and excess body weight (7.6%).
The Hidden Dangers of Medical Radiation
“CT is frequently lifesaving, yet its potential harms are often overlooked, and even very small cancer risks will lead to a significant number of future cancers given the tremendous volume of CT use in the United States,” the researchers write in their study, published in JAMA Internal Medicine.
The research team examined 93 million CT examinations performed on 62 million patients in 2023. Using data from multiple medical centers, they calculated the radiation doses for different scan types and patient groups.
For any individual patient, the risk from a single scan remains tiny. But with so many scans happening yearly, those small risks add up to a major public health issue. Adults receive 96.7% of all CT scans and would develop about 93,000 (91%) of the projected cancers.
Children face higher risks per scan because their developing tissues are more sensitive to radiation damage. The study found that “projected cancer risks per CT examination were estimated to be highest among children who underwent CT at younger than 1 year and decreased with age at exposure.”
Cancer Types and High-Risk Scans
The study identified lung cancer (22,400 cases), colon cancer (8,700 cases), leukemia (7,900 cases), and bladder cancer (7,100 cases) as the most common projected cancer types. For women, breast cancer ranked second highest with 5,700 projected cases.
Abdominal and pelvic scans were linked to the most projected cancers—nearly 40% of all cases despite being only 32% of CT exams. These scans expose several radiation-sensitive organs to substantial doses. Chest scans came in second, accounting for about 21% of projected cancer cases.
A practice called “multiphase scanning”—where multiple images are taken during a single CT appointment—substantially increases radiation exposure. According to the study, this occurs in 28.5% of examinations and “often these examinations could use single-phase scanning, which would lower doses without impacting diagnostic accuracy.”
Balancing Benefits and Risks
The study authors aren’t suggesting eliminating CT scans, which are crucial diagnostic tools. Rather, they emphasize the need for optimizing how we use them to minimize unnecessary radiation exposure while preserving their benefits.
This study’s projected cancer figures far exceed previous estimates. A 2009 analysis predicted about 29,000 future cancers from CT exposures in 2007. The jump comes from several factors: CT usage has increased 30% since 2007, researchers now have better data on scan types and radiation doses, and the current study included multiphase scanning, which earlier estimates missed.
Protecting Yourself
Medical groups have already launched initiatives to reduce unnecessary radiation exposure, including the Image Gently campaign for pediatric imaging and Choosing Wisely recommendations that identify overused tests.
Experts recommend asking these questions before a CT scan:
- Is this scan necessary?
- Could I have an ultrasound or MRI instead, which don’t use radiation?
- Has a similar scan been done recently that could be used?
- Will the scan use the lowest reasonable radiation dose?
The medical community now faces a challenge: maximizing the benefits of CT technology while minimizing its risks. As the study concludes, “Justification of use and optimization of dose, including consideration of the need for multiphase examinations, are the tenets of CT imaging and must be applied uncompromisingly to mitigate potential harm.”
Paper Summary
Methodology
Researchers used data from the University of California San Francisco International CT Dose Registry, which collected information from 143 U.S. hospitals and outpatient facilities across 22 healthcare organizations. They analyzed detailed information about CT examinations, including patient age, sex, body measurements, scanner type, and technical parameters. Using this data, they estimated organ-specific radiation doses for different types of CT scans categorized by body region and clinical indication (26 categories total). They then applied these findings to estimate the total number of CT scans performed in the U.S. in 2023 using the IMV Medical Information Division CT Market Outlook Report data. Finally, they projected lifetime cancer risks using the National Cancer Institute’s Radiation Risk Assessment Tool, which is based on risk models from the National Research Council’s Biological Effects of Ionizing Radiation VII report.
Results
The study found that approximately 93 million CT examinations were performed on 61.5 million patients in 2023, with adults accounting for 96.7% of scans. These CT examinations were projected to result in approximately 103,000 future cancers over patients’ lifetimes. Although children have higher risk per scan, adults account for 91% of projected cancers due to much higher scan volumes. The most common projected cancers were lung cancer (22,400 cases), colon cancer (8,700 cases), leukemia (7,900 cases), and bladder cancer (7,100 cases). Abdomen and pelvis CT scans contribute the most to cancer risk (37,500 cases, or 37% of projected cancers). The researchers conducted several sensitivity analyses, with projected cancer numbers ranging from 80,000 to 127,000 under different assumptions.
Limitations
The study relied on modeling rather than direct observation of cancer outcomes, which would require decades of follow-up. The risk models are based primarily on Japanese atomic bomb survivors, raising questions about transferability to the U.S. population. The researchers note they made conservative assumptions in several areas, such as using a lower percentage of pediatric examinations than some sources suggest. The study also didn’t account for patients’ underlying health conditions that might affect their life expectancy and thus their lifetime cancer risk, though they did exclude examinations performed in patients’ last year of life.
Funding and Disclosures
The research was supported by awards from the National Cancer Institute, the Patient-Centered Outcomes Research Institute, and by residual class settlement funds from a legal case (April Krueger v. Wyeth Inc). Dr. Smith-Bindman disclosed being a co-founder of Alara Imaging Inc, a company focused on improving clinical and operational aspects of health systems, including radiation dose monitoring. She noted that Alara Imaging played no role in the study and that this work doesn’t overlap with Alara’s commercial activities.
Publication Information
The study, “Projected Lifetime Cancer Risks From Current Computed Tomography Imaging,” was published online in JAMA Internal Medicine on April 14, 2025. It was authored by Rebecca Smith-Bindman, MD, and colleagues from the University of California San Francisco, University of California Davis, University of Florida, and other institutions.
