Should I “upgrade” to digital or 3D? A mammography guide


Susan Dudley, PhD, and Caitlin Kennedy, PhD
Caitlyn Brooks and Christina Silcox, PhD

 

Woman_receives_mammogramEvery year over 200,000 women in the U.S. are diagnosed with breast cancer, and every year breast cancer that has spread from the breast to other parts of the body (“late stage” or “metastatic” breast cancer) kills about 40,000 women.1 When breast cancer is detected early—before it has spread—it is easier to treat and women have a much better chance of surviving breast cancer. For now, mammograms are the best way of screening women for breast cancer.

Forty million mammograms are performed each year,2 but the technology is evolving. Depending on where a woman lives, she may be able to choose from among three different types of mammography. Does it matter what kind of mammogram she gets?

Digital vs. Film Mammography

Digital cameras have replaced the older, film-based cameras for most Americans. Mammography has also gone digital. As of October, 2015, over 95% of accredited mammography machines in the US were digital.2 For a patient, the mammography experience is about the same with 2D digital or film. But if you have a choice, is one better than the other?

2D digital and film mammography have been directly compared in several large studies. One, published in 2015 in the American Journal of Radiology, reviewed over 3 million screening mammograms performed in the US and found that the two methods are equivalent. Other studies have shown the same result.3,4,5 Since digital mammograms are stored as computer files, copying and retrieving them may be easier, and the images may be linked to your electronic health record.

A New Type of Digital Test: 3D Mammography

3D mammograms, also known as tomosynthesis or “tomo,” use the same x-ray technology as regular “2D” mammograms. The procedure is the same from the patient’s point-of-view, although it will take a few seconds longer. In both 3D and 2D mammograms, the breast is compressed between two plates. In 2D mammograms, which take images only from the front and side, this may create images with overlapping breast tissue. Because 3D mammography provides images of the breast in “slices” from many different angles, finding abnormalities and determining which abnormalities may be important may be easier with 3D tests. On the other hand, 3D mammography is more expensive than 2D, and your insurance may charge you more if you use 3D.

In 2013, the FDA decided that a low-dose 3D digital mammography was accurate enough to be used by itself, without also using 2D technology. 2D digital images can be obtained from the 3D mammogram data without the need for a separate test.

Differences between 2D and 3D Mammograms

Most research has compared the 3D mammogram findings combined with the 2D mammogram, compared to 2D alone. Most of that research was funded by Hologic and is performed on Hologic mammography machines, because theirs were the first to be FDA approved in the U.S. We do not know if the results would be similar with other companies’ mammography machines.

The results of the studies showed that the combination of 3D and 2D was more accurate than 2D digital or film mammograms, although the difference in accuracy was tiny for each patient.6,7,8,9,10,11 Just as importantly, women who undergo screening with 3D+2D mammography are less likely to be called back for more testing due to a suspicious finding that turns out not to be cancer. This means fewer false scares.7,8,12

The results of combining 3D and 2D are not very relevant today, since most women will undergo one or the other, rather than both. Experts no longer recommend undergoing both at the same time, since that increases the dose of radiation, which could potentially increase the risk of developing cancer in the future.

Comfort

Film, 2D digital, and 3D mammography involve the same amount of physical discomfort.

Cost

2D screening mammograms are free for patients covered by healthcare insurance under the Affordable Care Act. Some insurers will not cover 3D mammograms, and others charge women a surcharge. However, Medicare began covering 3D mammography in 2015 and some states are beginning to mandate coverage.13

Radiation exposure

The 3D test takes a few seconds longer than 2D digital or film mammography (adding a few seconds of discomfort). The amount of radiation exposure is slightly higher for combining 3D and 2D mammograms. The newer, low-dose 3D-only mammograms use less radiation than a 2D mammogram.

Because digital mammography—2D and 3D—is relatively new, no one has really figured out what all the health risks and benefits are, including the added cancer risk for women with larger breasts who may need additional images and therefore get more exposure to radiation.

Even if 3D mammography is more accurate, does it save lives?

Mammography detects cancer but it also can detect abnormalities, many of which are not dangerous. Detecting those abnormalities often results in unnecessary anxiety, testing, and even treatment. These issues are being considered by experts from across the U.S. as they debate whether lesions called Ductal Carcinoma in Situ (DCIS), for example, should be considered cancer or not, and whether they should be treated or just monitored closely.14

One large study7 in 2014 that was funded by the 3D mammography device company did not show an increase in DCIS detection rates using 3D+2D mammography versus 2D alone. However, a new, smaller study that was independently funded did show an increase in DCIS detection.8 This is an issue for patients to consider, because when doctors and patients discover abnormalities, even if they present very little risk or an unknown risk in the future, they usually undergo treatment. That unnecessary “over-treatment” has risks.

The Bottom Line

There is no evidence of any difference in cancer detection with 2D digital versus film mammograms. Combining 3D+2D mammography is very new and most of the published research was conducted by the company that is selling the machines. Based on their studies, 3D + 2D may be better at detecting cancer, and reduce call-backs for more testing with abnormalities that turn out not to be cancer. Although potentially important when millions of women are undergoing mammography, those differences are very small for individual patients (perhaps 2 in 1,000 instead of 1 in 1,000). Although most women today will undergo either 3D or 2D but not both, there is very little information on the accuracy of low-dose 3D mammography alone.

It is important to remember that experts now agree that most women under 50 do not need annual screening mammography. See our 2015 Update: When should women start regular mammograms? 40? 50? And how often is “regular”? for more information.

 


Related Content:
2015 Update: When should women start regular mammograms? 40? 50? And how often is “regular”?
DCIS: Mostly good news
Breast implants and mammography: what we know and what we don’t know

 

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  10. U.S. Food and Drug Administration. “Summary of Safety and Effectiveness Data (SSED): Selenia Dimensions 3D System.” http://www.accessdata.fda.gov/cdrh_docs/pdf8/P080003S001b.pdf (Accessed November 20, 2013).  
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