Film mammography has been the workhorse for more than 35 years to examine women for breast cancer. Of the 33.5 million mammographic studies completed each year, approximately 70 percent of those are obtained for screening purposes. At this time, the vast majority are acquired on analog imaging equipment because, according to the National Cancer Institute (NCI), only 8 percent of breast imaging centers currently use digital machines despite the first FDA clearance in 2000. But that is changing.
Five letters seem to have brought full-field digital mammography (FFDM) to the tipping point — that moment writer Malcolm Gladwell describes as when a trend crosses a threshold, tips and begins to spread like wildfire. While “wildfire” may be a bit strong to describe the adoption of medical technology, DMIST has served to validate the positives of FFDM: dramatically improved image quality with lower radiation dose, higher technologist and patient satisfaction, improved interventional efficiency and the benefits of image manipulation. DMIST has reassured many in the radiology community that this technology that has been gaining strength in smaller clinical studies now has the numbers of the masses behind it. That last push facilities needed to acquire it has arrived.
In October 2001, the Digital Mammographic Imaging Screening Trial (DMIST) began accruing more than 40,000 women study subjects who had no signs of breast cancer in 33 sites across the United States. The research protocol, sponsored by the National Cancer Institute (NCI) and coordinated by the American College of Radiology Imaging Network (ACRIN) was designed to compare film mammography with scans that were acquired on digital mammography units. The results, that were published in October 2005 in the New England Journal of Medicine, suggested three categories of women who appear to benefit from the use of digital mammography:
- Those under the age of 50, no matter the level of breast tissue density involved
- Those of any age with heterogeneously (very dense) or extremely dense breast tissue
- Pre- or peri-menopausal women of any age
The results of the DMIST study suggest that digital mammography may be better at detecting breast cancer than traditional film mammography for these specific categories of women. Approximately 65 percent of the women in DMIST fit into one of these three sub-sets — with 40 percent of those women classified as having dense breast tissue. During the course of the study, 335 women were diagnosed with breast cancer.
In terms of sensitivity, DMIST found that both digital and film mammography had the ability to tell if cancer is present about 70 percent of the time in the overall study population using conventional methods for measuring sensitivity in a breast cancer screening trial. However, for women with dense breasts, sensitivity was rated at only 55 percent for film mammography versus 70 percent for digital mammography.
The initial results of the DMIST study have certainly stimulated discussion of digital mammography technology among the women’s health and radiology communities and may encourage additional breast centers to purchase digital systems. Consumers, largely women, are more aware of the DMIST results and anecdotally many mammography centers say they are getting more requests for digital mammograms from a more educated public. According to the FDA Mammography Quality Standards Act (MQSA) website in February, of the 8,874 certified mammography facilities, 865 of them were using a total of 1,210 accredited FFDM units.
Personnel in these centers are quite enthusiastic in describing the adoption of this technology and report many affirmative experiences while offering cautionary and smart advice for those who choose to follow.
Positive aspects of digital adoption
The basic advantages of digital mammography as compared to film mammography include the improved ease of image management and storage, combined with a lower radiation dose that does not compromise diagnostic accuracy.
Steven Poplack, MD, co-director of the breast imaging center at Dartmouth-Hitchcock Medical Center in Lebanon, N.H., explains that with their Hologic Selenia system they have experienced better penetration through the dense breast giving them improved contrast within the image through use of digital technology. “When you look at a dense heterogeneously or extremely dense breast, digital to film screen side by side, the images of the digital just ‘wow’ you in terms