AYESHA RASCOE, HOST:
X-rays and CT scans have revolutionized medicine. Doctors can look inside the body and diagnose diseases even before people feel ill. But medical imaging that uses radiation comes at a cost. A new study published in the journal JAMA Internal Medicine has found that the 93 million CT scans performed in 2023 in the U.S. are projected to cause about 100,000 future cancers. Dr. Rebecca Smith-Bindman is the lead author of the study, as well as a radiologist and a professor of epidemiology at the University of California at San Francisco. Thank you so much for joining us.
REBECCA SMITH-BINDMAN: Thank you so much for the invitation.
RASCOE: So can you explain briefly, how do CT scans work?
SMITH-BINDMAN: Absolutely. So a conventional radiograph, like an X-ray of the chest or the arm - you have X-rays that come from the front and go to the back of the person and just go in one direction to take an image. A CT scan, by its very design, uses much more X-rays than a simple radiograph 'cause the X-rays basically are emitted going around the patient in a full circle in a machine that looks like a doughnut. And it uses many, many more X-rays 'cause the X-rays are continuously surrounding the patient. Inherently, it uses a lot more X-rays than conventional imaging does.
RASCOE: So how did you determine that CT scans will cause about 100,000 cancers in a year?
SMITH-BINDMAN: So the study is a modeling study, and such a study is only as good as the inputs. We had very accurate inputs on the number of scans that were performed annually. We know the types of scans that were performed based on the UCSF International CT Dose Registry that collected dose information of about 10 million scans, and we calculated the future cancer risk from each study using a National Cancer Institute model.
No model is perfect, but based on the results, I don't believe the uncertainty changes our overall conclusion, which is that a small proportion of cancer - perhaps 5%, give or take - comes from CT scanning. Reducing unnecessary scans or reducing the doses per scan could reduce this number.
RASCOE: And so this is a model because it's very hard, if someone gets cancer, to say, you got it from this place, right?
SMITH-BINDMAN: That's impossible. There's no radiation signature where we could say, oh, you have a cancer, and we can tell where it came from. So what we're estimating is how many extra cancers would come from radiation for CT, but we can't say from an individual patient what their cancer came from.
RASCOE: A lot of people hearing this may be like, I just got a CT scan, and you're telling me that now it could cause cancer. I guess, like, are you suggesting that we don't get CT scans?
SMITH-BINDMAN: So I'm suggesting perhaps we don't get so many. And in many instances, it's absolutely the right and best test to make a rapid and accurate diagnosis. But the use of CT continues to rise. There's been about a 35% growth in CT imaging in the last 10 years. And most physicians agree that CT scanning is overutilized, but we haven't done very much to reduce overuse.
And part of the way to reduce overuse is for patients to ask their doctors if a CT scan is ordered, do I really need the scan? Is it this important? How is it going to change the treatment that I get? Do I need it now? Can I postpone it to later? Or is there another test like an MRI or an ultrasound that could replace this test? And when CT is the right test, then this risk is worth it.
RASCOE: You know, I mean, doctors can be very intimidating to some people, and if the doctor says you need a CT scan, you'll go, well, I want to be safe.
SMITH-BINDMAN: First, I want to apologize for my entire specialty. Sorry that we are intimidating. Second, the lab that I work with at UCSF created a website, KnowYourDose, to help patients with that question. And we have a whole bunch of videos and scenarios to help patients ask their physicians these questions exactly. Do I really need these tests? And if I need the test, can we do it at a lower dose? But basically, you're not so much pushing back and saying I don't want the scan, but you're rather asking to understand why you need the scan.
And I completely understand that patients want to get the best care they can, and I'm sort of arguing that we need a little bit more dialogue between patient and physician. As a field, we will respect our patients. And so if our patients say, we want you to use less dose, most radiologists will be accommodating.
RASCOE: Dr. Rebecca Smith-Bindman is a professor at the University of California at San Francisco Medical School and the lead author of a new report on CT use and cancer. Thank you so much for joining us.
SMITH-BINDMAN: Thank you so much for having me. Transcript provided by NPR, Copyright NPR.
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