Definition of Therapy, external beam radiation

Therapy, external beam radiation: Radiation focused from a source outside the body on the affected area (a cancer) within the body. It's much like getting a diagnostic x-ray, but using a more potent x-ray beam and giving it over a longer period of time per dose with usually multiple doses given over multiple days.

Source: MedTerms™ Medical Dictionary
http://www.medterms.com/script/main/art.asp?articlekey=9831
Last Editorial Review: 9/20/2012