Radiation therapy is the use of high energy, penetrating radiation (x rays, gamma rays, proton rays, and neutron rays) to kill cancer cells.

The primary purpose of radiation therapy is to eliminate or shrink localized cancers (as opposed to cancers that have spread to distant parts of the body). The aim is to kill as many cancer cells as possible, while doing as little damage as possible to healthy tissues. In some cases, the purpose is to kill all cancer cells and effect a cure. In other cases, when cures are not possible, the purpose is to alleviate pain by reducing the size of tumors that cause pain.

For some kinds of cancers (for example, Hodgkin's disease, non-Hodgkin's lymphoma, prostate cancer, and laryngeal cancer), radiation therapy alone is the preferred treatment. However, radiation is often used in conjunction with surgery, chemotherapy, or both, and survival rates...