Digital mammo proves better than film-screen for diagnosing DCIS

The largest population-based study to date comparing film-screen mammography and full-field digital mammography has found the digital approach is superior for visualizing microcalcifications deemed crucial to diagnosing ductal carcinoma in situ. No other significant difference in the diagnostic capabilities of the digital and analog approaches was identified.

Though previous studies have shown digital mammography is as good as film when it comes to detecting breast cancer, the current study is still important due to its size, according to Dr. Marcela Bohm-Velez, an assistant professor of radiology at the University of Pittsburgh.

The study solidifies previous findings, she said.

Out of 367,600 screening exams performed over five years in Utrecht, the Netherlands, 56,518 were digital. The researchers detected breast cancer in 1927 women; 317 of the cases were detected by digital mammography enhanced with computer-aided diagnosis software (Radiol 2009 July 31 e-pub ahead of print).

Screening was conducted at regular two-year intervals and each exam was double read. Both are pertinent factors in the study's importance, according to Dr. Nico Karssemeijer, an associate professor of radiology at Radboud University in Nijmegen, the Netherlands, and lead author of the study.

"A strong point of the study is the fact the same group of radiologists was reading both film and digital in parallel during the whole study period," he said. "This largely reduces risk of bias."

At initial screenings, digital detected cancer at a rate of 0.77% and film at a rate of 0.62%. At subsequent readings digital detected cancer at a rate of 0.55% and film at a rate of 0.49%.

The real difference between digital and film comes from the ability to detect ductal carcinoma in situ. Film-based screening detection of DCIS was 0.12% in initial exams and 0.08% in subsequent exams. Digital mammography DCIS detection was 0.22% in initial exams and 0.12% in subsequent exams.

The increase in DCIS findings relates to better detection of microcalcifications using full-field digital mammography, Karssemeijer said.

"We found better detection of microcalcification clusters led to increased detection of invasive cancers without visible sign of mass or density," he said.

Recalls based on microcalcifications found with digital mammography were double those for film-screen mammo. The percentage of invasive cancers with microcalcifications as the only sign of malignancy jumped from 8.1% with film-screen mammography to 15.8% with digital mammo.

"This shows that improved detection of microcalcifications with full-field digital mammography is beneficial for earlier detection of invasive cancers," Karssemeijer said. As a result of the study, the Netherlands is currently transitioning its screening program from film to full-field digital mammography, according to Karssemeijer.

"The new system uses a uniform and centralized screening environment, which is unique because of its size: two million women participate in the program," he said.