Population-based study finds digital mammography equal to film

Digital mammography is at least as good as screen-film mammography for detecting breast cancer, according to a population-based screening program study presented at the RSNA meeting by Irish researchers.

Dr. Niamh Hambly of the department of radiology at Mater Misericordiae University Hospital in Dublin and colleagues retrospectively reviewed the performance of full-field digital mammography for 26,593 women out of 163,031 women screened for breast cancer. The Irish National Breast Screening Program invites women between the ages of 50 and 64 for screening mammography every two years.

Though the program was implemented in 2000, it became the first fully digitized screening service in the world in April 2008. Hambly and colleagues performed a retrospective analysis on the women screened between January 2005 and September 2007 to compare the recall rate, biopsy rate, cancer detection rate, and positive predictive value for digital versus film. Results were presented at the 2008 RSNA meeting.

The researchers found a recall rate of 3.95% in women undergoing digital screening and 3.23% in those undergoing film screening. The cancer detection rate for digital was 6.24 per 1000 women and 5.48 per 1000 for film. Of the cancers detected by digital mammography, 22.3% were ductal carcinoma in situ. Of the cancers detected by screen-film mammography, 18% were DCIS. The positive predictive value for women recalled for assessment and subsequently diagnosed with cancer was 15.8% for digital and 16.9% for film, according to Hambly.

"This study shows the cancer detection rate is significantly higher in digital mammography. Both patient groups were drawn from the same population, and the only variable was mode of documentation," she said.

Digital is superior to screen-film mammography in women between the ages of 50 and 64, she said.

The findings intrigued session comoderator Dr. D. David Dershaw, director of breast imaging at Memorial Sloan-Kettering Cancer Center in New York City.

"I think it's valuable to have an increasing number of screening studies with digital that are all showing us essentially the same kinds of information: higher callback rate, higher diagnosis of cancer, much higher diagnosis of DCIS, and increased conspicuity of calcifications but really kind of a small difference between the two," he said.