No woman wants to hear the words, "We'd like you to come back for another mammogram," but many do. Typically 10 to 15 percent of the tens of millions of women screened for breast cancer each year are asked to return for more thorough diagnostic mammograms because of a suspicious finding on the first set of images.
But a technology called digital tomosynthesis, now being evaluated at several U.S. medical centers, could slash the recall rateand possibly reveal tumors that don't appear on a mammogram or are too small to be picked up by a radiologist, researchers reported at this week's annual meeting of the Radiological Society of North America.
Mammography relies on two X-ray views of the breasttop to bottom and side to side. In conventional mammography, the X-ray images are stored on film. Digital mammography, recently approved by the Food and Drug Administration for general use, converts the images to data that can be analyzed, but the number of views is unchanged. Digital tomosynthesis, by contrast, creates a series of 15 to 20 images, stored as digital data, as a moving X-ray beam travels in a semicircle from one side of the breast to the other. The images are then combined to produce a series of 3-D pictures that can be viewed one by one or as a sort of movie.
In a study of 98 women who received digital tomosynthesis as well as a repeat mammogram following an abnormal initial mammogram, the new technology was as effective as or better than mammography 88 percent of the time. In fact, if tomosynthesis had been used to screen the women originally, 40 percent of the recalls might have been avoided, reported lead study author Steven Poplack, associate professor of diagnostic radiology and obstetrics and gynecology at Dartmouth-Hitchcock Medical Center in Lebanon, N.H.
At Dartmouth-Hitchcock, said Poplack, about 100 women are called back out of every 1,000 screened, and 20 then have a biopsy. Five of the 20 have cancer. If digital tomosynthesis were used to screen them, 40 of the 100 callbacks might not have to be made, eliminating untold emotional stress.
In the study, tomosynthesis also exposed a cancer in one woman that had been missed initially and could not be found on the mammograms even when the images were carefully re-examined by imaging specialists. That's not unusual. Mammography misses 10 percent to 20 percent of cancers in women without symptoms, according to the American Cancer Society.
The study was funded by Hologic, one of the companies developing tomosynthesis systems. Others include GE Healthcare, which displayed a model at the radiology meeting that has been undergoing trials at Massachusetts General Hospital.
The GE machine has appeal beyond technical capability. Many women do not go for regular mammograms because of the discomfort they experience when the breast is compressed to allow the X-rays to penetrate uniformly and to spread out the breast tissue. GE's system, according to a company representative, applies about half the usual force. "The breast must be kept from moving, but it does not have to be compressed," he said. The Hologic system employs a typical amount of compression, according to Poplack. "Adequate compression is the key to good data," he said.
See our guide on breast cancer for more information.