Breasts deemed "dense" in a mammogram tend to have less fatty tissue and more connective tissue, breast ducts and glands, doctors say. About 40 percent of women between the ages of 40 and 74 have dense breasts. Lester Lefkowitz/Getty Images hide caption

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Radiation therapy is effective in treating breast cancer but typically requires dozens of visits over five to seven weeks. A newer protocol takes just three weeks. Antonia Reeve/Science Source hide caption

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Life online is all about sharing images. Being able to share medical images would make health care a lot easier, patients say. Science Photo Library/Corbis hide caption

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