In film mammograms, the images of your breasts are recorded on large sheets of black and white film. In digital mammograms, the images are recorded into a computer. Digital mammograms are thought to offer two advantages over film mammograms:
Usually two images are taken of each breast (four total images) in both digital and film screening mammograms. Sometimes more images are needed to provide a good reading.
In the large study reviewed here, researchers analyzed how much radiation 5,102 women were exposed to during screening mammograms. The women were participating in a much larger digital mammography study called Digital Mammographic Imaging Screening Trials (DMIST). Nearly 50,000 women were part of DMIST from October 2001 through October 2003.
The researchers found that 21% of women who had digital mammograms needed more than four images taken while only 12% of women who had film mammograms needed more than four images. Among women who needed only the usual four breast images, women who had digital mammograms were exposed to an average 22% less radiation than women who had film mammography. But when the researchers evaluated the average radiation exposure of all of the women, including those who needed extra images, the average radiation exposure with digital mammography was only 17% lower than with film mammography.
There were large differences in the level of radiation exposure needed to produce a good breast image, depending on the manufacturer of the mammogram equipment.
Also, the average amount of pressure applied to the breast to produce a good image was less with digital mammograms.
The researchers also noted that advances have been made in digital mammogram technology, so the results of this study (from 2001 to 2003) may be different today. Still, these results may be important for researchers comparing the overall risks and benefits of different breast cancer screening approaches.
When developing your breast cancer screening plan, you and your doctor will likely discuss the availability of digital mammography in your area and whether it offers advantages for you. Here are some questions you may want to ask your doctor:
Together you and your doctor can decide on the best screening approach for you based on your unique situation. To learn more about mammography techniques, visit the Breastcancer.org pages on Mammograms.
Digital mammography exposes women to a lower radiation dose than standard film mammography, but digital imaging is likely to require more than four normal views in about 20% of women screened, according to a subset analysis of data from a study of almost 50,000 women.
The mean glandular dose per view was 2.37 mGy for film mammography versus 1.86 mGy for full-field digital mammography, a difference of 22%, R. Edward Hendrick, PhD, of the University of Colorado-Denver, and colleagues reported in the February issue of the American Journal of Roentgenology.
But only 12% of women screened with traditional mammography required more than four normal views compared with 21% of the women imaged with digital systems.
When the need for additional views was factored in, they wrote, the difference in radiation exposure between the two modalities dropped to 17%, 4.14 mGy for digital versus 4.98 mGy for standard mammography.
Furthermore, these differences were not standard -- there was a wide variation across manufacturers. For example, the average mean glandular dose per view was 3.77 for Fischer digital versus 5.03 for Hologic Selenia, which was also the only manufacturer in which the digital dose was higher than the standard film dose.
Doses were compared on a manufacturer basis -- film mammography versus digital:
The analysis of parameters and radiation dose was culled from data collected by the American College of Radiology Imaging Network Digital Mammographic Imaging Screening (DMIST) trials, which enrolled 49,528 women from October 2001 through October 2003.
The primary goal of DMIST was to compare the accuracy of the two technologies. The results, reported in 2005, found that digital mammography was superior for younger women and for women with dense breasts, but when results from all 50,000 women were considered there was no significant difference.
This latest study was based on technical data compiled on 5,102 women of which 4,366 cases yielded "clean" data that were included in the analysis.
The researchers did find a significant difference in the pressure each modality exerted on the breast. "Mean compression force was 10.7 dN for screen-film mammography and 10.1 dN for full-field digital mammography (5.5% difference, P<0.001)," they wrote.
There was also a 1.7% statistically significant difference in mean compressed breast thickness -- 5.3 cm for screen-film mammography versus 5.4 cm for digital.
But the difference in breast compression, while statistically significant, was "likely clinically insignificant," Hendrick and colleagues concluded.
The authors noted that the study was limited by the advances in imaging technology -- since the study was conducted, film manufacturers have introduced "new screen-film combinations, such as double-sided screens and double-emulsion films that were not available during DMIST."
For that reason, "breast dose along with image quality and other parameters should be carefully compared between existing screen-film mammography and any new [digital] system being considered for integration into a breast imaging practice."
The DMIST trial was supported by the National Cancer Institute and by the Lynn Safe Breast Cancer Research Foundation.
Hendrick disclosed that he is a consultant to GE Healthcare on digital breast tomosynthesis and other breast imaging projects not related to DMIST.
Primary source: American Journal of Roentgenology Source reference: Hendrick RE et al "Comparison of Acquisition Parameters and Breast Dose in Digital Mammography and Screen-film Mammography in the American College of Radiology Imaging Network Digital Mammographic Imaging Screening Trial" AJR 2010; 194: 362-369
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