Radiation therapy (also called “radiotherapy,” “irradiation,” or simply “radiation”) is another standard treatment that many patients with a brain tumor will receive. Radiation therapy involves the use of x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors by damaging their DNA. Radiation sources can be placed within the brain at the time of surgery to target residual tumor cells (internal radiation therapy or brachytherapy through applications such as GammaTile or Xoft). Radiation may also come from a machine outside the body (external-beam radiation therapy). As with surgery, there are now many newer and emerging radiation technologies, tools, and techniques, including radiosurgery (also called stereotactic radiosurgery) and proton beam therapy.