A new radiation therapy can extend the lives of men with the most advanced form of prostate cancer, a large study has found.

The treatment is an isotope of radium that zeros in on cancer cells that have spread to bones. The radium, which mimics calcium, binds with minerals in a patient’s bones, where it delivers radiation that destroys cancer cells without inflicting as much damage to surrounding tissues as older radiation therapies.

The study, published in the New England Journal of Medicine, involved a large group of men with late-stage prostate cancer who were expected to live less than a year. Those who were given the drug, however, saw their median survival time increase to nearly 15 months, a “substantial 30 percent improvement,” said Dr. Chris Parker, the lead author of the new study and a consultant clinical oncologist at the Royal Marsden Hospital and the Institute of Cancer Research in England, both in London.