Radiation therapy is used to treat breast cancer painlessly and noninvasively. During treatment, high-energy X-rays are delivered to a patient’s breast cancer safely and effectively. Side effects are usually minimal, and most patients return to routine activities immediately after each treatment. Radiation therapy serves as an effective treatment for breast cancer, working within cancer cells to damage their ability to multiply. Several factors determine candidacy for radiation therapy treatment including the stage of the cancer, potential side effects, age and overall health. Sometimes a combination of treatments is the best plan for treating breast cancer.