gamma knife

External Beam Radiation Therapy

External beam radiation therapy is a type of radiation therapy that directs a beam of radiation from outside the body toward cancerous tissues inside the body.

Because of recent innovations that allow for customization of the angle and shape of the radiation beam(s), these treatments can be designed in such a way that they destroy tumor cells while sparing the surrounding normal tissue from adverse effects of radiation.

There are several types of external beam radiation therapy:

Intensity Modulated Radiation Therapy (IMRT)
3D Conformal Radiation Therapy (3DCRT)
Gamma Knife Radiosurgery
CyberKnife Radiosurgery

Depending on the specific treatment, external beam radiation therapy is typically administered daily over a period of 5 to 6 weeks. Most people get treatment once a day for five days each week. Patients do not feel anything during the treatment itself, which is given as an outpatient procedure.


This content was reviewed by UCSF radiation oncologist David Raleigh MD, PhD.