Digital Mammography: Is Newer Always Better?
By Rachel Walden
You may have noticed last time you got a mammogram that your facility uses digital imaging rather than traditional X-ray film. Why is that? And, is there any benefit to the newer techniques?
In 2009, when the U.S. Preventive Services Task Force (USPSTF) reviewed the evidence and updated its recommendations on breast cancer screening, it concluded there was not enough evidence to assess the benefits and harms of digital versus film mammography, due to a lack of studies on the effectiveness of the two methods. The USPSTF noted that both formats may detect some cancers that are not identified by the other, but that overall detection is similar for many women. It found that the chance of false-positives (indication of cancer where it doesn’t exist) is similar in both types.1,2
The USPSTF recommended that, for women with no increased risk of breast cancer, the decision to start screening before age 50 should be an individual one rather than a general recommendation. Normal-risk women were recommended to have breast cancer screening every two years from age 50 to 74.3
The Digital Mammographic Imaging Screening Trial (DMIST) is the most important trial of digital vs. film mammography for breast cancer screening to date.4 Published in 2005, the study compared the accuracy of breast cancer detection in film vs. digital mammography in almost 50,000 women. The researchers concluded the two methods have similar accuracy and that neither is clearly better, overall. Neither technology was able to detect 100 percent of the cancers examined.
The researchers found digital to be the better tool for women who have very dense breast tissue, are under age 50 (regardless of breast density), or are pre-menopausal or peri-menopausal. Digital mammography had no benefit in terms of accuracy for women with all three criteria (i.e., under age 50, with dense breast tissue, and who are still menstruating). There was no difference in accuracy by race, breast cancer risk, or type of digital machine used.
But, DMIST was not designed to compare any difference in mortality among women who had different imaging types — so it can’t answer whether digital mammography could save more lives than film. The National Cancer Institute notes that, while some health care providers recommend women with a very high risk of breast cancer (i.e., women with BRCA1 or 2 genetic mutations or extremely dense breasts) get digital rather than conventional mammograms, no studies have shown that digital is better at reducing these women’s risk of death.5 The Institute of Medicine (IOM) has named research to compare the effectiveness of film and digital mammography alone with that of mammography-plus-MRI for screening high-risk women as a priority for future comparative effectiveness research.6
Although the USPSTF found insufficient evidence to specifically address digital mammography, its recommendation suggests that, for normal-risk women, there is not much evidence of a big difference between film and digital mammography in detecting breast cancer.
When examining a new medical technology, one consideration is how much the technology costs compared to how many years of quality life may be gained by using it. The DMIST trial indicated that screening all women with digital mammograms was not cost-effective, because digital costs more and doesn’t improve health outcomes when used so broadly. Targeting women for digital mammography based on age (i.e., using digital for women under 50) appears to be more cost-effective than using film or digital for all women. The study concluded that a shift to all-digital mammography “has the potential to result in health gains for younger women (especially those with dense breasts) possibly at the expense of older women (especially those with non-dense breasts).”7
Unfortunately, providers may not give women a choice. Some health care systems have simply switched over to digital, and individual providers may refer women for a mammography without indicating which type they will receive. In some cases referrals for digital mammography may be linked to a provider’s investment in the machines, since evidence suggests that doctors are more likely to recommend expensive medical technologies when they have a financial stake in them, even if the procedure isn’t supported by medical evidence.8 Medicare also reimburses more for digital screening exams than for film, creating a financial incentive for clinics and hospitals to conduct digital scans instead of film ones.”9,10,11
But, digital mammography does have some benefits over film. Digital files can be enhanced and manipulated in ways film cannot. The electronic images can be readily shared with clinicians at other locations, which may particularly benefit rural and underserved communities using telemedicine for reading and interpreting these mammograms.12 Finally, digital mammograms may have a slightly lower radiation dose than film (although this may not be meaningful in terms of radiation-related risks, since the radiation dose with either type is very low).13,14
These potential benefits may not justify a switch to digital mammography for all women. The USPSTF notes: “Consumer expectations that new technology is better than old may obscure potential adverse effects, such as higher false-positive results and expense. No screening trials incorporating newer technology have been published.”15
When your doctor refers you for a mammogram, ask:
- Are you referring me for a digital or a film mammogram?
- If you are under 50 years of age: Why do you believe I need a mammogram at this time? Am I in a higher risk group? (This is important if you don’t know that you have any factors that may put you at increased risk).
- Do you have a financial stake in the mammography facility?
You can also ask your insurer if a film mammogram would cost you less. Many women’s screening mammograms are completely covered by insurance, but costs can vary widely, so it’s good to confirm what the charges will be in advance.16
Rachel R. Walden, MLIS is a medical librarian and blogger for Women’s Health News and Our Bodies Our Blog.