Digital Mammography: Direct Outperforms Computed Radiography

Laurie Barclay, MD

May 14, 2013

For breast cancer detection, digital direct radiography (DR) is more effective than computed radiography (CR), according to a cohort study published online May 14 in Radiology. However, DR is equivalent to screen-film mammography (SFM) for breast screening in women aged 50 to 74 years.

"Digital mammography was implemented progressively in Ontario starting in 2006, and since that time there's been no evidence in the literature to suggest that CR did not perform as well as DR," lead author Anna M. Chiarelli, PhD, senior scientist in Prevention and Cancer Control at Cancer Care Ontario in Toronto, Canada, said in a news release.

Recently, digital mammography has been in more widespread use than SFM; however, few studies have evaluated the type of detector used in digital mammography. DR is an online system that includes a detector as an integral part of the mammographic unit to allow reading of the digital image in real time. CR is an offline system using a cassette-based removable detector and an external reading device to generate the digital image.

Using data from the Ontario Breast Screening Program, the investigators identified concurrent cohorts of women aged 50 to 74 years who were screened with DR (n = 220,520), CR (n = 64,210), or SFM (n = 403,688) between 2008 and 2009. After a 12-month follow-up, the researchers compared performance between cohorts, using SFM as the referent cohort, and applied mixed-effect logistic regression to evaluate associations.

Detects 10 Fewer Cancers per 100,000

DR and SFM had similar cancer detection rates (4.9/1000 [95% confidence interval (CI), 4.7 - 5.2] vs 4.8/1000 [95% CI, 4.7 - 5.0]). For CR, however, the rate was significantly lower (3.4/1000 [95% CI, 3.0 - 3.9]; odds ratio, 0.79 [95% CI, 0.68 - 0.93]).

"CR was 21 percent less effective than DR," Dr. Chiarelli said in the news release. "This could result in about 10 fewer cancers detected per 10,000 women screened..... There may be several technical reasons reported by others for the lower effectiveness of CR, including loss of spatial resolution, or sharpness, and increased image noise, or granularity."

Compared with the recall rate for SFM (7.4%; 95% CI, 7.3% - 7.5%), the rate for DR was higher (7.7%; 95% CI, 7.6% - 7.8%), and that for CR was lower (6.6%; 95% CI, 6.5% - 6.7%). Although positive predictive value was lower for CR (5.2%; 95% CI, 4.7% - 5.8%) than for SFM (6.6%; 95% CI, 6.4% - 6.8%), the adjusted odds were not significant.

Study strengths include large sample size and use of concurrent cohorts. Limitations include nonrandomized design, lack of data on radiologists, inability to examine mammographic density using the standard Breast Imaging Reporting and Data System classification, and insufficient power in some of the stratified analyses. In addition, the findings may not be generalizable to symptomatic women or to those who are not aged 50 to 74 years.

"Although DR is equivalent to SFM for breast screening among women aged 50–74 years, the cancer detection rate was lower for CR," the authors conclude. "Screening programs should monitor the performance of CR separately and may consider informing women of the potentially lower cancer detection rates."

The Canadian Institutes of Health Research funded this study. The institution of the senior study author receives money from GE Healthcare for collaborative research in improved imaging techniques for breast cancer The other authors have disclosed no relevant financial relationships.

Radiology. Published online May 14 2013.

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