- A new study suggests that CT scans may slightly increase the lifetime risk of developing cancer.
- The researchers say the cumulative effects of ionizing radiation over time should not be ignored.
- Other experts say the risk of cancer from CT scans is minimal, and these imaging exams are an important diagnostic tool for various cancers.
A commonly used computerized scan may slightly increase cancer risk over a person’s lifetime.
That’s according to a new study published in JAMA Internal Medicine, an online publication of the American Medical Association.
Researchers from the United Kingdom and the United States report that computed tomography (CT) scans could drive an estimated 103,000 future cancer cases.
If true, that would mean CT scans would account for 5% of all new cancer diagnoses in the United States.
Researchers reported that the number of CT exams performed each year in the United States has increased by more than 30% since 2007.
They said the technology can save lives by detecting cancer early, but they expressed concern over the potential dangers of low doses of ionizing radiation over time.
“CT can save lives, but its potential harms are often overlooked,” said Rebecca Smith-Bindman, MD, a radiologist and professor of epidemiology and biostatistics as well as obstetrics, gynecology, and reproductive sciences at the University of California San Francisco (UCSF), in a press statement.
“Given the large volume of CT use in the United States, many cancers could occur in the future if current practices don’t change,” added Smith-Bindman, the study’s lead author.
CT scans help detect cancer early
In response to the new research, the American College of Radiology (ACR) stated that no published studies directly link CT scans to cancer.
They added that there are many benefits to diagnostic tests such as CT scans.
“Medical imaging exams — including CT — are a primary factor in declining cancer death rates, and are directly linked to decreased hospital mortality rates and greater life expectancy. Scans reduce invasive surgeries, unnecessary hospital admissions and length of hospital stays,” the ACR said in a press statement.
“Americans should not forgo necessary, life-saving medical imaging and continue to discuss the benefits and risks of these exams with their healthcare providers,” the ACR added.
Richard Reitherman, MD, a radiologist and medical director of breast imaging at MemorialCare Breast Center at Orange Coast Medical Center in California, agreed. Reitherman wasn’t involved in the study.
“CT scans aid in the diagnosis and treatment of conditions that may otherwise lead to increased morbidity and mortality if CT scans are not used,” Reitherman told Healthline.
“Since the harms that patients would otherwise experience by not using CT scans is not addressed, the clinical application of these results [of the study] is not actionable,” he added.
Patricia Nguyen, MD, an associate professor in the Division of Cardiovascular Medicine at Stanford University in California, stressed the benefits of CT scans. Nguyen wasn’t involved in the study.
“CT tests are important for evaluating patients who present with symptoms and signs of cancer,” she told Healthline. “When the benefits outweigh the risks of a test and the test is clinically indicated and will inform decision making (e.g., lead to a diagnosis that then leads to treatment), then a CT test should be performed.”
Calculating cancer risks from CT scans
In their study, the researchers used data collected from 143 hospitals and outpatient facilities between 2018 and 2020 and catalogued in the UCSF International Dose Registry.
From that, the researchers estimated there were 93 million CT scans performed on nearly 62 million people in the United States in 2023.
The researchers said that based on associated radiation risks, they estimate that CT scans in 2023 could be linked to 103,000 future cancer diagnoses.
They reported that radiation-induced cancers would be at a higher rate in children and adolescents than in adults.
They also estimated that the most common cancers among adults would be lung cancer, followed by colon cancer, leukemia, and bladder cancer. In females, breast cancer was the second most common, while in children, the most frequently projected cancers were thyroid, lung, and breast.
The highest number of cancers in adults was projected to come from CT scans of the abdomen and pelvis, followed by chest scans. In children, cancers were linked to CT scans of the head.
The researchers acknowledged that the cancer risk from CT scans remains minimal and needs to be examined over decades of large-scale follow-up studies.
However, they said some changes should be considered in how often these diagnostic tests are used.
“Our estimates put CT on par with other significant risk factors, such as alcohol consumption and excess body weight,” Smith-Bindman said. “Reducing the number of scans and reducing doses per scan would save lives.”
Reitherman noted that the American College of Radiology has implemented value-based appropriateness criteria for CT scanning.
“Current practice includes measures of radiation dosage for each exam,” he said. “This process is reducing the number of examinations and dosages. This is an ongoing process that will reduce the theoretical impact of radiation-induced cancer.”
What to know about CT scans
CT scans combine a series of X-rays into 3-dimensional pictures.
These medical imaging tests use ionizing radiation to create cross-sectional images of selected areas of the body.
These pictures can show internal organs, bones, blood vessels, and soft tissues.
CT scans are used to detect tumors, blood clots, internal bleeding, and infections.
These scans usually require more exposure to radiation than common X-rays. However, they also provide medical professionals with a more detailed look inside a person’s body.
CT scans, for example, are considered the most beneficial exam for early detection in lung cancer.
“Lung cancer screening constitutes the largest proportion of screening examinations,” Reitherman explained.
“Lung cancer screening is performed on patients that have a significant risk for developing lung cancer due to chronic smoking histories. Screening CT scans in this group of patients has been shown to decrease the stage at diagnosis and therefore improve outcomes. Benefit far outweighs the risk.”
CT scans are also considered the “gold standard” for detecting pulmonary embolisms, blood clots that block blood flow within the lungs. They are also useful tools in getting accurate images of the brain.
Nguyen said that people should “always limit their exposure to radiation.” In addition, they should ask questions of their doctors, such as:
- What is the total radiation of this test?
- Is a dose report available?
- Is there an alternative test that doesn’t produce radiation?
Reitherman also urged people to be involved in their medical decision making.
“Patients should be advocates for themselves in discussing every form of diagnostic testing with their physicians. This would include CT scans as well as lab tests, etc.,” he said. “Conversations about risk and benefits are important so that individuals can optimize benefits and reduce potential risks.”
