Scientists estimate the number of lives saved by finding cancer early through mammography screening far outweigh the number of lives lost through cancers caused by X-ray radiation from the scans, according to a new study.

Using models based on typical doses delivered by digital mammography units, researchers estimate that among a large population of women, screening results in a net gain of more than 10,000 life years. The results appear online and in the January issue of Radiology.

"Our study shows that the risk of cancer associated with routine screening in women age 40 and over is very low, especially when compared to the benefits associated with early detection," said lead author Martin J. Yaffe, a Stanford University-trained professor of medical biophysics with the University of Toronto.

With his colleague James G. Mainprize, Yaffe created a model based on 100,000 women receiving a radiation dose of 3.7 mGy delivered to both breasts, with each woman getting one annual scan from age 40 to 55, and then biannual screening until age 74.

According to the model, screening would result in 86 radiation-induced cancers, 11 of them fatal, with 136 life years lost. That is, 136 women would die one year sooner than expected, or about 13 women would die 10 years sooner than expected.

But screening would also save 497 lives, for a total of 10,670 life years gained by finding and treating the cancers early.

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