Despite lacking FDA approval, breast digital tomosynthesis is already making waves in the breast imaging community. A recent study from the University of Pittsburgh Medical Center published in the American Journal of Roentgenology shows combining breast digital tomosynthesis with full-field digital mammography lowers recall rates. The modality could also be especially helpful in imaging women with dense breasts, according to several radiologists. The FDA is still testing and collecting data on digital tomosynthesis, so only a handful of sites in the U.S. are using the modality. Siemens, Hologic, and GE have installed their machines at institutions around the country to gather the information they will need to gain FDA approval. Digital tomosynthesis has already been approved for use in Europe. Even though breast digital tomosynthesis can be found only in scattered places in the U.S., mammographers are already buzzing about the new approach because it enables 3D reconstruction. This capability allows cross-sectional visualization of breast tissue and reduces the difficulty caused by superposition, the overlapping of tissue when viewed in projection mammograms. With breast digital tomosynthesis, the breast is compressed in standard fashion while an x-ray tube arcs over the breast, capturing images at every angle. Typically, 10 to 20 exposures are made during a scan of five seconds or less. The individual images are projections through the breast at different angles that are reconstructed into slices. Besides reducing recall rates, as the AJR study showed it can (AJR 2009;193:586-591), other potential advantages of the modality include improving cancer detection in women with dense breast tissue and reducing the number of negative biopsies. Combining digital breast tomosynthesis with full-field digital mammography reduced recalls by 30% in the University of Pittsburgh study. Use of digital breast tomosynthesis alone reduced recalls by 10%, although the researchers said the observed decrease was not statistically significant. The studies were read by eight radiologists, all of whom performed at a higher sensitivity (93%) and specificity (64%) when viewing and rating the digital tomosynthesis studies of the 125 subjects. Using full-field digital mammography alone they had substantially lower sensitivity (88%) and specificity (60%). Readers require extensive training in digital breast tomosynthesis to recognize abnormalities as well as widely varying normal tissue that can cause negative findings.
“Even radiologists quite familiar with the procedure who have substantial experience in viewing digital breast tomosynthesis images may have difficulty with a correct diagnosis in a fraction of actually negative cases, generating recommendations for recall about sites not seen as abnormal on FFDM images,” said Dr. David Gur, a professor of radiology at the University of Pittsburgh and lead author of the study. However, the radiologists' performance levels-particularly recall rates-will improve with increasing experience and appropriate feedback, he said. An area with enormous potential is in imaging women with dense breasts, according to Dr. Stamatia Destounis, an attending radiologist at Elizabeth Wende Breast Care center in Rochester, NY. Destounis is testing a digital tomosynthesis system by Hologic. “I'm hoping digital tomosynthesis is the next frontier after digital mammography because it could answer all the questions about very dense breast tissue that I can't answer with mammography,” she said. The modality could be used in the screening population for women with dense breasts, replacing mammography altogether, according to Destounis. “I think we'll able to reach higher sensitivity and make the mammogram more accurate for them by using digital tomosynthesis,” she said. It also allows the radiologist to see masses and microcalcifications in very fine detail, according to Destounis. Digital tomosynthesis has the potential to replace mammography altogether, according to Dr. Joseph Lo, an associate professor of radiology and biomedical engineering at Duke University. Lo uses a digital tomosynthesis machine provided by Siemens. “Mammography is the standard when it comes to breast cancer screening because it still has the best sensitivity, lowest cost, and highest throughput.” Lo said. But it's got a lot of problems, missing in the range of 30% of cancers and producing a high number of false positives, he said. “Very often mammography will result in false alarms that require bringing the patient back for further studies, which requires more radiation, more compression, and then, in some cases, more procedures-biopsies and so on,” he said. “We've known about all of this for a long time, but we haven't had the technology to do anything about it.” Because of the potential advantages associated with digital tomosynthesis, both scientists and clinicians are anxious to get it in the marketplace as soon as possible, Lo said.
FIGURING IT OUT Digital tomosynthesis also comes with drawbacks. Most of the kinks seem to stem from learning how to use the machine, Lo said. All are relatively easy problems to solve. Another question is whether there should be one or two views of the breast. Mammograms are traditionally done from two different angles per breast. But if tomosynthesis is a truly 3D technique, theoretically the radiologist shouldn't need to look at the breast from two different angles. However, digital tomosynthesis is not truly 3D. “There's a lot of anecdotal evidence, none of it published yet, that suggests you do see more cancers by taking a second look,” Lo said. The problem is that a second look doubles the radiation dose, scan time, and interpretation time, Lo said. Still, he suggests that all these glitches associated with digital tomosynthesis will be worked out as more people use it and conduct research. Despite the small research base to date, there is an emerging consensus on the modality's value. “For something that's not FDA-approved, the preliminary results from each of the three major vendors and countless academic groups have all shown very similar improvements in performance,” Lo said. “I don't think a lot of people realize how unusual that is.” Lo thinks the number of false positives will be drastically reduced. “[That] is going to completely change how we do things,” he said. Current clinical practice dictates that if a radiologist sees anything that cannot definitively be ruled out as cancer, the patient must have a workup. “That's a really very different way of practicing medicine than if you had the kind of tools that would tell you, 'Well no, this is really nothing. Don't worry about it. I can show you in 3D this is nothing.' We're just not able to make these kinds of decisions today,” Lo said. As of Aug. 3, Hologic chair and CEO Jack Cumming said there were no updates regarding FDA approval for digital tomosynthesis. The firm postponed its panel meeting with the FDA, which had been slated for June. “We feel this is appropriate for several reasons, such as to augment our clinical information, and, ultimately, to strengthen the technology's position in the marketplace,” he said. Hologic wants to have multiple, phased clinical indications for use approved, which may encourage the modality's adoption process, he said. “We believe we will enhance our market position,” Cumming said. “We believe this process will culminate with a version of the product and indications for its use with broad clinical utility.” Though the FDA seems to be dragging its feet on approving breast digital tomosynthesis, it will happen eventually, Lo said. “It's taken a lot longer than all of us thought, but I think there's a groundswell of support that's beginning to build,” he said. “People just need to be patient and hang on.”