Digital mammography lowers dose to breast

The average dose of full-field digital mammography is less than that of screen-film mammography, according to a March report by the FDA.

Facilities with digital mammography scanners reported an average dose of 1.52 mGy from measurements taken between 2000 and 2003, the Average Glandular Dose in FDA-approved FFDM Systems report said.

Another FDA report listed the average screen-film dose for 2003 as 1.76 mGy. The screen-film dose might be higher in 2005, however, as the trend has seen doses increase, said the 2003 report, Dose and Image Quality in Mammography: Trends during the First Decade of MQSA.

In 1995, the average dose for screen-film mammography was 1.5 mGy, increasing to 1.6 mGy in 1997, 1.65 mGy in 1999, and 1.76 mGy in 2000 and 2003. Statistical testing by the FDA showed that facilities inspected in 2002 were actually administering higher doses on average than facilities inspected in 1995, despite improved techniques and image quality.

The report noted, however, that the technical aspects of screen-film mammography are fairly optimized and that the recent modest increase may not be significant. It added that digital-based mammography technologies including computer-aided detection may offer further dose improvements.

Although the FDA approved the first FFDM unit for marketing in January 2000, it had no mechanism in place for accrediting the new technology. Temporary measures allowed for facilities already certified for screen-film mammography to prove themselves for FFDM by verifying training requirements and performing physics tests.

One phantom test involved measuring the average glandular dose for a craniocaudal view of the standard breast. The dose could not exceed 3 mGy.

Records compiled by the Division of Mammography Quality and Radiation Programs from June 2000 to September 2003 show that the FDA extended the certificates of 264 screen-film facilities to cover 337 FFDM units.

The agency compiled a summary of the average glandular dose for 318 of those units:

• maximum dose: 2.98 mGy

• minimum dose: 0.57 mGy

• average dose: 1.52 mGy

• standard deviation: 0.36 mGy

In February 2003, the FDA granted permission for the American College of Radiology to accredit the GE Senographe 2000D digital mammography unit, followed by the Fischer SenoScan in August and Lorad Selenia in September.

As of May 1, 2005, there were 631 certified facilities with FFDM units and 855 accredited scanners.

For more information from the Diagnostic Imaging archives:

CAD's role in breast screening shifts from quantity to quality

Report urges sweeping changes to quality standards

Facilities save money with digital mammography

Breast centers tune up for peak performance