External Radiation (External Beam Therapy)

External beam radiation therapy is a treatment that precisely sends high levels of radiation directly to the cancer cells. The machine is controlled by the radiation therapist. Since radiation is used to kill cancer cells and to shrink tumors, special shields may be used to protect the tissue surrounding the treatment area. Radiation treatments are painless and usually last a few minutes. Radiation therapy may be given alone, or in combination with surgery and/or chemotherapy. Radiation may also be used to ease symptoms such as pain, bleeding, or blockage.

External beam radiation therapy device

With external radiation (external beam therapy), radiation is administered by a medical linear accelerator (invented at Stanford) that points the radiation directly at the tumor. You will lie on an X-ray table with the same immobilization devices in place that were used in the simulation process. A specially-trained radiation therapist controls the machine. Special shields may be made to protect the tissue surrounding the treatment area, or sometimes protective devices are incorporated into the "head" of the treatment machine.

External beam radiation therapy is delivered in multiple "fractions." Usually, treatments are delivered on a daily basis, five days per week. The duration will depend on the type of cancer and its location. At the outset, confirmatory X-rays are taken in the treatment position to confirm that the treatments have been designed properly. These are then reviewed by the radiation oncologist. Subsequently, each daily treatment requires only several minutes and you will not likely be in the treatment room any longer than 15 minutes.

External beam radiation therapy imaging

Radiation treatments are painless, you feel absolutely nothing during a treatment. Although you are alone in the treatment room while the machine is turned on, you will be monitored with audio and video by the radiation therapist.

The two major types of radiation beams are photons and electrons. Both are produced by the linear accelerator. In general, photons (X-rays) travel completely through a body or tissue. Electrons penetrate to only a defined depth. Photons or electrons are chosen depending upon the location of a tumor. They may be used, in combination.

External beam therapy includes:

  • 3-D conformal radiation therapy
  • Intensity modulated radiotherapy (IMRT)
  • Electron beam radiotherapy
  • Total body irradiation (TBI)
  • Total lymphoid irradiation (TLI)