Newer digital mammograms may deliver significantly lower radiation doses than conventional film mammograms, especially for women with larger and denser breasts, U.S. researchers said on Thursday.

A study of nearly 50,000 women that compared digital mammography systems to film mammograms found the radiation dose was about 22 percent lower on average with the newer digital mammography exams.

"The ability to reduce the radiation dose for many women is another step forward for breast cancer screening with mammography - which saves thousands of lives each year," Edward Hendrick of the University of Colorado-Denver and a consultant to General Electric's GE Medical Systems, said in a statement.

The results were part of the Digital Mammography Imaging Screening Trial of 49,528 women, which in 2005 found that digital mammograms detected up to 28 percent more cancers than film mammograms in women under 50 who have not gone through menopause and in women with dense breast tissue.

Dr. Carol Lee, chairwoman of the American College of Radiology Breast Imaging Commission, said the previous study showed that the performance of digital was equivalent or slightly better in certain groups.

What is new, she said, is "that can be achieved with overall a lower radiation dose."

Both film and digital mammograms make X-ray images of the breast, but digital mammograms are collected and stored on a computer, making them easier to access than conventional film mammograms.

Lee said generally, the radiation dose from film or digital breast mammograms is not large enough to be worrisome, and women should not skip getting a recommended mammogram if digital mammography is not available in their area.

But in general, she said, lowering the radiation dose is preferable. "We certainly want to keep radiation dose as low as possible and still achieve the desired goal of a good image," Lee said in a telephone interview.

In the study, researchers used digital mammography equipment made by Fischer Imaging Corp, Fujifilm Medical Systems, GE Healthcare and Hologic Inc.

Lee, who was not involved in the research, said only the systems made by GE and Hologic are still available, and said companies have made significant advances in the technology since the data in the study were collected, suggesting the newer machines may deliver an even lower radiation dose.

"Unfortunately, studies and information lag behind the actual practice," Lee said.

Besides lower radiation exposure and better performance for certain women, Lee said digital mammography offers the same kinds of advantages that digital photographs have over pictures taken with older film technology.

"You can zoom in. You can change the contrast level and things like that. When you took a picture with your old film camera, what you took is what you got," she said.

The study was funded in part by the National Cancer Institute and published in the American Journal of Roentgenology.