Radiologists who use 3-D, also known as tomosynthesis, say its drawbacks are worth the greater accuracy. By itself, 3-D mammography delivers about the same amount of radiation as standard digital 2-D mammograms.
But when the FDA approved the new device, it said 3-D could be used only as an add-on to standard mammograms, essentially doubling the low radiation dose. The FDA made 3-D an add-on only because there is not enough information yet about whether 3-D screenings detect cancers as well as 2-D mammograms do. Therefore, 2-D remains the standard of care and provides unique benefits for clinicians, such as familiarity and the ability to compare images from previous years.
“The 3-D image doesn’t replace the standard 2-D mammogram,” says Julianne Greenberg, a radiologist at Washington Radiology Associates, which has begun telling women who come in for their standard 2-D screening that they can add a 3-D mammogram to it for $50. “Three-D is added value to an already existing, really good technology.”
In a conventional mammogram, the breasts are compressed and X-rayed four times: side to side and top to bottom, for both the left and the right breast. To take the 3-D images, an arm of the machine sweeps in an arc around the breast during each of the four compressions, taking anywhere from 20 to 60 pictures to produce a 3-D rendering of the breast. These images look almost like holograms; radiologists can spin and flip them around on a computer screen, searching for cancer in the tissue and lymph nodes.
When looking at a 2-D and a 3-D image of a breast together, radiologists showed a 7 percent improvement in their ability to distinguish between cancerous and non-cancerous cases, according to two studies that the FDA considered during its approval process.
More accurate detection reduces the rate of false positives. In the United States, about 10 percent of women who have a screening mammogram will be called back for additional imaging, such as a sonogram or more mammography, according to the FDA. The vast majority of those women do not have breast cancer (about four cases of breast cancer are found for every 1,000 women who are screened, Greenberg says), but they have to cope with the fear and anxiety of having abnormal mammograms and perhaps undergoing more invasive testing.
“It’s terrifying for a patient,” Greenberg says. “It’s anxiety-producing. It’s inconvenient. It’s additional radiation exposure. It’s potential for a biopsy for something that really is benign.”
Washington Radiology Associates began offering tomosynthesis in August 2011. Close to half of patients have been choosing to spend the extra $50, Greenberg says, which insurance does not cover. Aetna, for example, considers tomosynthesis “experimental and investigational because of insufficient evidence of its effectiveness.”