Introduction to Radiotherapy Radiotherapy is a type of cancer treatment that uses radiation to kill cancer cells. It is also used to shrink tumors, reduce pain, or help control symptoms. The radiation can come from a machine outside the body (external beam radiation) or from radioactive material placed in the body near cancer cells (internal radiation, brachytherapy). Radiotherapy has been used to treat cancer since the late 1800s. It is one of the most common treatments for many types of can...