CT Scans and Cancer Risk, with Rebecca Smith-Bindman, MD

October 30, 2014
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In this podcast, Dr. Rebecca Smith-Bindman explains the cancer risks associated with computed tomography, or CT, scans and the importance of discussing the risks and benefits of this imaging test with your doctor.



ASCO: You're listening to a podcast from Cancer.Net. This cancer information website is produced by the American Society of Clinical Oncology, known as ASCO, the world's leading professional organization for doctors that care for people with cancer.

In this podcast, Dr. Rebecca Smith-Bindman explains the cancer risks associated with computed tomography, or CT, scans and the importance of discussing the risks and benefits of this imaging test with your doctor. Dr. Smith-Bindman is a Professor in Residence of Radiology, Epidemiology and Biostatistics, Obstetrics, Gynecology and Reproductive Medicine at the University of California, San Francisco. ASCO would like to thank Dr. Smith-Bindman for discussing this topic.

ASCO would like to thank Dr. Smith-Bindman for discussing this topic.

Dr. Smith-Bindman: Hi, my name is Rebecca Smith-Bindman and I'm a Professor of Radiology and Biomedical Imaging, Epidemiology, and Biostatistics, and Health Policy at the University of California, San Francisco. I am primarily a radiologist who focuses on evaluating the risks and benefits of medical imaging.

 So to help guide what tests we should use more of because they're really helpful, and what tests we should use fewer of because they can be associated with some harms, today I'm going to give you a little bit of background on computed tomography, or CT scans, and what you really need to know about these tests in terms of do they have any associated risk.

A CT scan is basically a very sophisticated new type of x-ray we've been using for about 25 years, and it basically takes an x-ray circumferentially around the body so you get a lot of images that get put together to create very detailed images of internal organs. X-rays use ionizing radiation, and ionizing radiation is basically energy, and it's energy that's strong enough to change DNA. It's defined as the type of energy in a certain spectrum that has the capacity to cause damage. Most of that damage is relatively minor and can be fixed internally. Your own repair mechanisms can fix it. But some of the damage cannot be fixed, and that ends up leading to future cancers down the line.

There have been many studies of the harmful effect of radiation in a whole lot of different populations. Basically, the exposures that we use in medical imaging are enough that they will cause cancer in some individuals. Not a large number of individuals, but it's been estimated in the ballpark of 3 to 5% of cancers in the United States that come from radiation from medical imaging. So whenever you're using imaging tests, CT scans in particular, you need to balance the benefit of that test, how much information you're going to gain, how it's going to change your management, against the risk.

The risk is very well known. The doses of radiation that are used in a CT scan can be 500 or 1000 times higher than a plain x-ray. The doses are higher, and therefore the risks are higher. And what I advise my patients, and what I conduct our research studies on, is to try to understand how to maximize the benefits of imaging while minimizing the harm.

On the one hand, I don't want patients to be afraid of CT scanning. CT scanning is very helpful in many situations. It's become one of the mainstays of medical imaging, and it's very helpful in cancer patients to understand where disease may be located, where their cancer has spread to other parts of the body, whether cancer is responding to a particular treatment or if it's not responding, if we need to switch treatments.

It can be very helpful, but at the same time that it can be helpful, we probably overuse medical imaging and CT scanning. We image too much. And so the trick for the patient and the oncologists and all caring physicians is to determine how to balance. How to use imaging when it's going to be helpful, and how to avoid imaging when it's probably not going to add much to the patient's care, and therefore only delivers a small risk of radiation related carcinogenesis.

What I would advise patients is every time you're going to be getting a medical imaging scan, ask your physician why. Do I need this test? Why do I need this test? How is it going to help me in terms of your changing my management? If I need this test, do I need this test now or can I wait a longer period of time? We often image repeatedly in patients who have cancer before really that information is likely to change. So I've just imaged a month ago, I'm going to image again now, and nothing really has changed. Or when the information is not really going to change what you do. Sometimes a tumor will respond, but from an imaging perspective, it may not change on the image. And so having another image may not help information. So talk to your physician about whether you need the test. If you do need the test, do you need it now or can it wait? And sometimes, there are exams that don't use radiation, such as ultrasound or MRI, that can be used instead of CT scanning.

The other point that I wanted to add is, if you're having a CT scan, I think it's important to ask that that CT scan be done using the lowest radiation dose possible to answer the clinical question that's being asked in your case. But some of my research has focused on documenting the incredible variation in radiation dose that patients receive depending on where they go for evaluation. So if they go to one hospital, they may get a much higher dose than if they go to a lower hospital, and that extra dose won't really add to the care. It'll just lead to unnecessary risk. So I think it's really important that patients start raising this issue with physicians, with the technologists, with the radiologists, so that we in healthcare become aware that it's important to you to have the lowest dose possible for diagnosis.

So again, ask, is this study being done using the lowest dose possible to make the diagnosis that you need to make for me? So the bottom line is, yes, there is real risk of cancer associated with CT scanning, but that real risk is relatively small. However, we don't want to take any extra risks if we don't need to. Don't refuse imaging, but discuss with your physician what the best test is to have, and what the best timing is to do that test. Thank you very much.

ASCO: Thank you, Dr. Smith-Bindman. More information on imaging tests can be found at www.cancer.net. Cancer.Net is supported by the Conquer Cancer Foundation, which is working to create a world free from the fear of cancer by funding breakthrough research, sharing knowledge with physicians and patients worldwide, and supporting initiatives to ensure that all people have access to high-quality cancer care. Thank you for listening to this Cancer.Net Podcast.