“Generally, if a patient is getting a one-time CT to address a problem, the risk of that CT is very, very low,” said radiologist Mustafa Bashir, MD, associate vice chair for research in the department of radiology at Duke University Health System in North Carolina.
“The times we might get concerned are in repeated screening — for example, if a patient needs repeated scans annually or more frequently over many, many years. In those cases, we would want to consider radiation-free techniques like MRI,” said Bashir, the former director of MRI at Duke. “This is particularly true for children.”
CT scan use has risen dramatically in recent years, prompting researchers to explore potential cancer risks — though these studies (including the one mentioned above) can’t prove a causal link.
“There are no proven cases of cancer arising from diagnostic medical imaging that uses ionizing radiation,” such as X-rays or CT scans, said radiologists Michael N. Hoff, PhD, Kimberly Kallianos, MD, and Javier Villanueva-Meyer, MD, in a joint statement to WebMD. All three are professors at the University of California San Francisco, where the lead author of the latest study also works.
For that study, researchers estimated how many people nationwide get CT scans each year and then used mathematical formulas to estimate lifetime cancer risk linked to radiation exposure. They proposed that of the estimated 61.5 million people who got CT scans in 2023, eventually 103,000 would develop cancer linked to radiation exposure.
Bashir called the estimate “unrealistically high” and was also critical of the methodology, noting that it relied heavily on data from atomic bomb survivors.
“Assuming that many small injuries over time add up to the same risk as one massive injury is a known issue with these kinds of calculations,” Bashir said.
Usually, the CT scan is the right choice. “If CT is clearly indicated, the benefits likely far outweigh the risks,” said radiologist Rebecca Smith-Bindman, MD, the author of that latest study.
But sometimes, “alternative imaging options like ultrasound or MRI might be more appropriate,” said Smith-Bindman, a UCSF professor and director of the university’s Radiology Outcomes Research Laboratory. “Most estimates are that a third or more of [CT] scans are not necessary.”
Your move: Have an informed conversation with your health care provider about whether a CT scan is needed, Smith-Bindman said. Consider these key points.
How to Ask if You Really Need a CT Scan
Start the conversation before you even reach your appointment: Write down your questions — you can use the note-taking app on your smartphone — and bring them with you.
Here are the essential questions to consider:
- Why do you want me to get this test?
- What are you expecting it will show?
- How will this test affect my treatment?
- Do I need to get this test now?
- What are the potential harms of the test?
- Is there an alternate test that might give the same information (like ultrasound or MRI) that does not use radiation?
“Feel free to call their office and ask about how to set up a phone conversation with them,” Smith-Bindman said.
Remember, your doctor wants you to feel “prepared and comfortable for your exam,” Smith-Bindman said. “By being an active part of the conversation with them, you can ensure that you receive the care and answers you need.”
It’s also important to ask yourself whether you’re the one pushing for the scan.
“Patients seeking reassurance from a CT scan, especially when their clinician has indicated a low likelihood of finding actionable information, should be aware of the small cancer risk associated with the scan,” Smith-Bindman said.
Request the Lowest Dose Possible
Generally, doctors try to give patients the lowest dose possible for a CT scan — while still getting the images needed for accurate diagnosis.
A low-dose option is typically recommended if you don’t have symptoms — such as for lung and colon cancer screenings or monitoring chest nodules, said Smith-Bindman.
Still, it can be useful to remember that what’s considered “low” or “high” is relative.
“‘Low-dose’ CT is somewhat of a misnomer,” Bashir said. “There are some very low dose techniques, like those for lung cancer screening. In the abdomen, there is low-dose technique for renal stones.”
But today’s doses are “very low compared to what they were 15 years ago,” Bashir said. “So a standard scan using a current-generation CT scanner would have been considered low dose in the past.”
That dose typically goes down every three to five years as new technology is adopted, Bashir added — meaning “in five years, average doses will be lower than they are today.”
Talk to the CT Scan Technician
You’ve probably been told never to ask the technician “how things look” as you’re finishing up a scan. Only your doctor can provide results.
Tell the tech about your symptoms so they make sure the selected scan protocol is appropriate, Bashir said.
Also tell your technician if you have any medical needs — like pain, difficulty lying flat, or allergies — that could affect the process.
It’s also OK to ask the tech about dosage, Smith-Bindman said.
“Specifically, they should ask how many phases of the scan are planned,” she said. Generally, more phases means more radiation exposure. “If more than one phase is indicated, patients should ask the technologist to consult the radiologist about potentially limiting the scan to a single phase.”
After you’ve said your piece, then it’s time to listen: Following the tech’s instructions as closely as possible, such as for when to remain still and when to hold your breath, can help you avoid repeat scans.
When to Reconsider a CT Scan
If you’re having a hard time figuring out why you’d need a CT scan, that could be a red flag. “It’s important to understand the [clinical] question [behind the] imaging,” Smith-Bindman said. If a scan is not clearly clinically indicated, it may not be necessary.
For example: “Undergoing imaging simply to see what’s going on with a chronic problem is generally not a strong indication for a CT scan,” Smith-Bindman said. “And CT scans for assessment of cancer are often done more frequently than needed.”
Likewise, seeking a second opinion is not a good reason to get another scan — just have the initial scan results transferred from your first consult, even if it’s tedious.
Doctors might also avoid CT scans for “people with genetic predisposition to cancer who require lifetime screening, often of the whole body or the abdomen,” Bashir said. “In those cases, we do MRI instead.”
What CT Scans Are Really Good For
According to Hoff, Kallianos, and Villanueva-Meyer, the medical goals that CT scans excel at achieving are:
- Finding problems early, like detecting cancer when it’s easiest to treat.
- Planning and monitoring cancer treatment. Scans can show where the cancer is and how it’s responding.
- Avoiding surgery or other invasive procedures, such as those with exploratory goals.
- Ensuring treatment is precise. Scans can help guide the placement of needles or tubes to the right place, so treatment is effective.
- Getting answers fast. In life-threatening emergencies, such as with strokes, internal bleeding, or appendicitis, CT scans can aid with timely decisions.
“In trauma settings, CT scanning is fast, accurate, and capable of evaluating multiple clinical questions simultaneously,” she said. “However, even in trauma, there are decision rules to help physicians minimize CT use.”
For instance, a patient with shortness of breath, low blood oxygen, and a positive D-dimer blood test indicating a possible blood clot should undergo a CT scan to confirm the presence of a clot. But if the patient has already been diagnosed with a clot and is receiving treatment, then a follow-up CT scan may not be necessary, Smith-Bindman said.
“If patients and referring physicians insisted on lower doses, radiologists could significantly reduce the radiation exposure,” Smith-Bindman said.