Radiation therapy is the use of radiation to injure or destroy cancer cells.
The rays penetrate the body from the outside, and deposit energy in the tissues in its path. Some are killed, some are injured and repair themselves, and some are not affected. Normal cells are injured, but are often able to repair themselves better than cancer cells. Radiation therapy is also administered by radiation implants. The implants are placed in the cancer itself, or right next to it, and are usually left in place for several hours or several days and then removed.