Philly researchers say most women have a low risk of developing breast cancer from radiation exposure during a digital mammogram. But women with large breasts receive  more than twice as much radiation and require more views per examination.
 
The University of Pennsylvania study found that screening every 2 years instead of yearly and beginning at age 50  instead of 40 or 45,  lowers the likelihood of breast cancer induced by radiation in all women.
 
The group found that screening 100,000 women, ages 50 to 74, every two years, prevented 627 deaths. The radiation exposure from these screening exams, and any subsequent diagnostic work-ups, caused 27 breast cancer cases and 4 breast cancer deaths. 
 
Although screening 100,000 women annually from 40 to 74 years prevented 968 deaths, it also raised cancer risk five-fold, causing 100 additional radiation-induced breast cancers and 12 additional breast cancer deaths compared with screening every two years from age 50 to 74.