Research reveals that overuse of CT scans could account for one of 20 new US cancers

A groundbreaking study reveals that the vast amount of CT scans in the United States could cause more than 100,000 future cancer cases, posing urgent questions about when medical imaging can do more harm than good.

study: Risks of lifespan cancer from current computed tomography imaging. Image credits: Radiation Imaging/Shutterstock

New research published in Jama Internal Medicine The radiation dose currently used in US routine computed tomography (CT) trials is revealed using modeling to reveal that ultimately it will account for 5% of all new cancer diagnoses each year. This study estimates the range of 80,000 to 127,000 projection cancers based on sensitivity analysis, and a median estimate of approximately 103,000 future lifetime cancers from CT scans performed in 2023 provides a 90% uncertainty limit for these projections.

background

Computed Tomography (CT) is a widely recognized medical imaging test used for diagnostic purposes. CT scans are important imaging techniques used to diagnose cancer, detect bone damage, and guide treatment, but patients are exposed to certain levels of ionizing radiation that can increase the risk of cancer.

In this context, evidence shows that exposure to CT may increase the risk of blood and brain cancer in children. In adults, CT-related radiation exposure can cause DNA damage, which may increase the risk of cancer.

The risk of cancer from CT exposure depends on multiple factors, including radiation dose, body imaging, patient age, gender, weight, and acquisition technique.

In the US, routine CT scans performed in 2007 are predicted to cause approximately 29,000 future cancers in 2009. Since these estimates were made, routine CT scans have increased by more than 30% per year. The new study will use an updated modeling approach and more detailed test-level data to improve these risk estimates.

A team of researchers from the Cancer Institute at London, Washington, Seattle and the University of California, San Francisco, used up-to-date data on CT scans and doses to update previous predictions on lifetime cancer risks associated with CT.

The researchers used a publicly available radiation-induced cancer risk model developed by Professor Amy Bellington, the leader of the Clinical Cancer Epidemiology Group, to estimate the number and type of cancer expected in both children and adults for CT exposure. This prediction is based on the widely accepted National Academy of Sciences BEIR VII risk model in the field of radiological epidemiology and incorporates adjustments for latency, range of uncertainty, and differences in organ dose by age and gender.

Cancer risks associated with CT scans

Research forecasts for future cancer risk were based on CT scans of 93 million people in the US in 2023. These scans were predicted to cause around 103,000 cancer cases in the country, ranging from 96,400 to 109,500 uncertainty. Sensitivity analysis using alternative assumptions gave a broader range of 80,000-127,000 projection cancers.

Considering CT scans performed in 2.5 million children in 2023, approximately 9,700 cancer cases are predicted, with a 90% uncertainty range of 8,100-11,600. Although the risk of CT radiation-induced cancer was higher in children and adolescents, these tests were performed more frequently in adults and resulted in more predicted cancers in older adults.

Importantly, this study was excluded from risk prediction. This is because these patients have a limited life expectancy and are not at risk of developing radiation-induced cancer.

Model predictions show that the most common cancers between men and women are lung cancer, colon cancer, leukemia, and bladder cancer. However, in women, breast cancer was predicted to be the second most common cancer.

The most common cancers in adults were predicted to be attributable to abdominal and pelvic CT (reflecting 37% of projected cancer), followed by chest CT (reflecting 21% of predicted cancer). In children, projected cancer was more likely to be associated with brain CT scans.

With each scan, the risk of cancer is highest in younger ages, especially children exposed in children under 1 year old, but the majority of predicted cancer cases occur in adults due to the much higher frequency of CT use in that age group.

The importance of research

The study revealed that if CT scan usage frequency and radiation dose remain unchanged in the US for the next few years, it will be responsible for about 5% of all new cancers diagnosed annually in the country. This estimate refers to future lifelong cancers that are expected to arise from a year's worth of CT scan (2023) rather than an immediate diagnosis of the same year.

CT scans are potentially life-saving techniques used to monitor diagnosis and treatment. Considering the benefits, potentially harmful consequences are often overlooked in clinics.

The researchers emphasize that CT scans can have advantages that outweigh risk when they are clinically justified, doses adjusted to the patient's age, and organs are targeted.

The UK has strictly regulated CT scan usage. The radiologist reviews each scan request and performs scans only at clinically justified and optimized doses. These strict regulations result in scans of more than 250 people per 1,000 people in the United States, with fewer than 100 people per 100 people.

In this context, evidence shows that the benefits of CT scans can mask risk when used in target screening in healthy individuals such as lung cancer. However, researchers argue that cancer risk outweighs the potential benefits of full-body scans private clinics offer to healthy people.

“While CT scans are immensely beneficial in diagnostics and detecting many conditions, including cancer, they do involve exposure to ionising radiation that has been shown to increase the risk of developing cancer. It's important to note that for the individual patient, this increased risk is small, and the benefits far outweigh the risks if the scan is clinically justified. But when millions of CT scans are being carried out across the population, these small risks do add up. In the US, CT-related cancers now account for 5% of all cancers. Some of these cancers can be prevented by avoiding unnecessary scans and ensuring that the correct dose is used.”

“The UK's NHS has a much better system to ensure that CT scans are clinically justified, but we should not be satisfied. Many other countries in Europe and Australia also run scans. These numbers are on the rise.

“These future cancer risks can be reduced by reducing the number of CT scans (low value scans used, especially in situations that are unlikely to help patients), or by reducing doses per trial, a radiologist and professor at the University of California, San Francisco.

The authors emphasize that these risk estimates are based on established models and the best available data. However, they are predictions rather than direct observations, and include a range of uncertainties that reflect the limitations and assumptions of the modeling approach.