Breast center tests nation's first approved 3-D mammography device
By Debbie Bolles / April 1-10, 2011
Staying on top of the latest in imaging technology, UT Southwestern participated in trials of the nation’s first approved mammography device that takes three-dimensional images of the breast.
The Selenia Dimensions Systems device was used in clinical trials here for the past two years. These trials and others nationwide led to the Food and Drug Administration’s approval of the system Feb. 11.
“Even though the technology is now FDA-approved, it remains unclear whether it will replace conventional digital mammography,” said Dr. Phil Evans, professor of radiology and director of the Southwestern Center for Breast Care at the Harold C. Simmons Comprehensive Cancer Center. “The real issue is how big a game-changer this is in detecting breast cancer.”
Based on trial findings reported to the FDA, the device sometimes helps radiologists pinpoint cancer not detected in two-dimensional mammograms. Weighed against that benefit is the device’s higher radiation dose — about twice that of a conventional mammogram, but still below FDA limits.
“It is less useful in women whose breast tissue is fatty, and more useful in women with dense breast tissue,” said Dr. Evans of the 3-D device marketed by Hologic Inc. of Bedford, Mass., which also makes conventional digital mammography units.
In its approval process, the FDA evaluated results from two studies in which board-certified radiologists were asked to review 2-D and 3-D images from more than 300 mammography exams. According to the FDA, radiologists viewing both sets of images were better able to distinguish cancer compared with viewing 2-D images alone.
The combination of Selenia’s 2-D and 3-D images doubled the radiation dose the patients received. The FDA said the increase in cancer risk from having both types of mammograms is expected to be less than 1.5 percent compared to natural cancer incidence, and less than 1 percent compared to the risk from conventional 2-D mammography.
Though the device is still being used in one trial at the breast center, Evans said no decision has been made whether to purchase the device and use it for routine screening. Up to now, it has been used for research on loan from Hologic.
UT Southwestern concluded one trial with the machine in which women with dense breast tissue, including some who had been diagnosed with breast cancer, were scanned. In a second trial that is ongoing, 3-D mammograms are being offered to some women called back for additional evaluation after screening. In all, about 80 women have participated in trials of the device at UT Southwestern.
Dr. Evans said the 3-D mammogram takes only two to three seconds longer than a conventional mammogram. Some women have said the procedure is a bit more comfortable than a conventional mammogram, he added.
The imaging technology, called tomosynthesis, is best described as a combination of a mammogram and CT scan. The Selenia machine rotates to a 45-degree angle from either side of the top of the breast, taking 75 individual image slices. According to Hologic, these multiple-angle images reveal the inner architecture of the breast free from distortion typically caused by tissue shadowing or density. These images are then synthesized to show “slices” of breast tissue similar to a CT scan. The machine also takes conventional 2-D images for comparison.
The Selenia machine isn’t the first 3-D imaging device used for breast cancer screening at UT Southwestern. A 3-D breast ultrasound machine was evaluated in a research trial but its use was discontinued because “it was not a significant improvement over standard imaging,” Dr. Evans said.
As with that device, the tomosynthesis will have to prove its worth as a screening and diagnostic tool. “We need to see more of the data before making a decision,” he said. Standard imaging techniques for breast cancer detection and diagnosis include digital mammography, ultrasound, magnetic resonance imaging, and image guided biopsy.
Nearly 200,000 women will be diagnosed with breast cancer this year, according to the National Cancer Institute. The chances of a woman getting breast cancer are 1 in 8 over her lifetime.
But the survival rate is 98 percent when cancer is detected early and localized in the breast, according to NCI. That makes early-detection tools such as advanced imaging all the more important.
Dr. Evans holds the George and Carol Poston Professorship in Breast Cancer Research.