Radiation is a form of energy released in particles or waves. In high doses, radiation destroys cells or keeps them from multiplying.

Radiation therapy is a cancer treatment. Its goal is to kill cancer cells and shrink tumors. Unlike cancer cells, most of your normal cells recover from radiation therapy. Doctors try to protect normal cells by limiting the radiation dosage and spreading treatment out over time. When they use radiation machines, they shield as much of your body as possible while targeting the cancer.

The radiation for cancer treatment comes externally, from special machines, or internally, from radioactive substances that a doctor places in your body. Sometimes radiation is used with other treatments, like surgery or chemotherapy.