External beam radiation therapy uses penetrating beams of high-energy waves to attack cancer cells. External beam radiation targets the radioactive waves directly at the cancer. A machine outside the body delivers the radiation. High doses of radiation kill cells or keep them from growing and dividing. Cancer cells are more susceptible to radiation because they can’t repair the damage.

 
Radiation therapy can be used to treat many kinds of cancer in almost any part of the body. In fact, more than half of all people with cancer are treated with some form of radiation. Some cancers, however, are resistant to radiation. For some cancers, radiation therapy alone is the only treatment necessary. It can also be used as an adjuvant therapy, given after or used in combination with surgery or chemotherapy.

The radiation that destroys cancer cells can also destroy nearby healthy tissue. This results in side effect, such as skin changes and fatigue. Most side effects will subside after treatment is completed. The risk of side effects is usually less than the benefit of destroying the cancer cells.