Radiation Oncology or radiation therapy is a form of cancer treatment that uses radiation (strong beams of energy) to kill cancer cells or keep them from growing and dividing. Radiation therapy, including intensity modulated radiotherapy, may be used in conjunction with surgery or chemotherapy to treat cancer. Radiation is given either externally, through external beam radiation, or increasingly through internal radiation, also called brachytherapy.
Radiation therapy is sometimes used as the sole treatment for cancer, but it is usually used in conjunction with chemotherapy or surgery. Typically, radiation therapy involves small doses of radiation administered daily over a period of several days to several weeks. More than half of all cancer patients receive some radiation therapy as part of their treatment.