Study finds advantages in digital mammogram

More costly device works better for some women

September 17, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Digital mammograms are better at detecting breast cancer than traditional X-rays for some women, but most patients do just as well with a cheaper film X-ray, according to a large study released yesterday.

Researchers found that film and digital mammography were equally accurate for the general population. But for women in three groups - those with dense breasts, those under age 50 and premenopausal women - digital mammography was 28 percent more accurate.

The senior author of the $26 million study, which involved 50,000 women, said the results do not discredit film mammography and women should continue getting exams using either technology.

She pointed out that digital imaging is just as accurate for women in general and more accurate for some.

"Film mammography has been around for years, and it's still good. It's just that digital is better," said Dr. Etta Pisano, a radiology professor at the University of North Carolina.

The main issue now facing the medical community is that digital equipment as much as five times as expensive as film systems and still relatively rare. Only 8 percent of the nation's mammography centers have digital systems, according to the National Cancer Institute.

The Digital Mammographic Imaging Screening Trial compared breast exam results for 49,528 women who showed no signs of breast cancer when they enrolled in the study in October 2001.

The women were given both digital and film mammograms at 33 sites in the United States, including Johns Hopkins Hospital. Two certified radiologists interpreted the conventional and digital mammogram exams for each patient during an initial visit.

335 cancer cases

The women were given a single follow-up film mammogram one year later. About 335 women were diagnosed with cancer during the course of the study.

The results were released at a radiologists conference in Arlington, Va., yesterday and published online by the New England Journal of Medicine (www.nejm.org).

For the women who were most at risk for developing breast cancer, the researchers found no difference in accuracy between film and digital mammograms.

But some experts noted that for specific groups - such as those with dense breast tissue - the results showed striking differences. Digital mammography revealed evidence of cancer in up to 26 percent of the dense-breasted women when film mammography missed it, they said.

"Actually, I personally was stunned to see such a difference in outcomes," said Dr. Nagi Khouri, director of breast imaging at the Johns Hopkins Radiology Center, who conducted the trials here.

Khouri said there are very few digital mammography systems - nationally and in Maryland - because they're relatively expensive, costing up to five times as much as film-based systems.

"In my opinion, this will increase the move toward digital, but I think it's important to caution people against saying, `I don't want anything but a digital mammogram,'" he said.

Increase in sales

Companies that make digital mammography equipment - which first became available about six years ago - are gearing up for increased sales.

"I see this as an emerging market," said Vince Polkus, mammography product manager for GE Healthcare, which has been selling Full Field Digital Mammography equipment since 1999.

GE hopes to sell several hundred digital mammography devices over the next several years, he said. They cost $400,000 to $500,000 he said.

GE, Fuji Medical Systems, Fischer Imaging and Hologic digital mammography systems were all used in the trial. All except the Fuji system have been approved by the FDA and are available for clinical use.

Film mammography is based on traditional photographic techniques, in which an X-ray image is created directly on film. Once the film is exposed and developed, it cannot be significantly altered - which means that badly exposed images can't be adjusted.

Cancers overlooked

Previous studies have also shown that film can miss up to 20 percent of breast cancers detected by self-examination or a doctor's physical exam.

"With film, you can have some difficulty, from the way the cancer presents and from what surrounds it," Nagi said.

He explained that when a woman's breast is particularly dense, it presents a white background on an X-ray image that can make it hard to spot the tiny white dot that can signify the start of a cancerous tumor.

Like digital photography, digital mammography records an electronic image of the breast and stores it as data on a computer. Experts say that gives doctors the same flexibility that digital photographers have with snapshots.

"Digital allows you to adjust the brightness of the image and the relative contrast to enhance the image or any part of it," said GE's Polkus.

Advocates say digital images are also easy to transfer electronically between doctors' offices and require less radiation than film mammography.

No overnight change

But experts stressed yesterday that digital technology will not replace film mammogram overnight.

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