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External Beam Radiation
External beam radiation therapy (EBT) is a method for treating cancer that involves directing a beam of high-energy x-rays at the patient's tumor. The beam is generated outside the patient, usually by a linear accelerator. The goal of EBT is to destroy or shrink the cancer while minimizing damage to the surrounding normal tissue (1, 2).
Delivery of EBT requires a treatment team, composed of a radiation oncologist, a radiation physicist, a dosimetrist and radiation therapist. The administering of EBT is divided into three parts: simulation, treatment planning, and delivery. In the simulation stage, the radiation therapist takes x-rays or CT scans to assist the radiation oncologist in determining the size and dimensions of the tumor. The dosimetrist and the radiation oncologist next determine the ideal arrangement of beams to best treat the tumor. The patient is precisely positioned on the treatment couch using alignment lasers, and the radiation therapist may make marks on the patient's body to use as guides (1).
In the treatment planning stage, the specifics of the radiation delivery process is determined by the dosimetrist, radiation physicist, and the radiation oncologist. They will determine the precise amount of radiation both the tumor and the normal tissue will encounter, which involves several factors, including how long the beams should be left on. They may make a 3-D computer mapping of the tumor or utilize intensity-modulated radiation therapy (involving a moving treatment couch) to assist in treating the tumor with precision (1).
After the simulation and treatment planning have been completed, the treatment can begin. The treatment process takes from 10 to 30 minutes, and most often the bulk of the time is spent positioning the patient. The patient is positioned on the treatment couch in the same manner as determined in the simulation. Certain immobilization devices may be utilized to help the patient remain still (1).
The patient's diagnosis determines the treatment schedule, but typically it is once or twice a day, for about five days a week, lasting for two to nine weeks. The treatment itself is painless, and side-effects will vary depending on the area being treated and the doses of radiation involved (1, 2).
- "External Beam Therapy." From the Radiological Society of North America, Inc.'s (RSNA) website. Available: http://www.radiologyinfo.org/en/info.cfm?pg=ebt&bhcp=1 (Accessed July 29, 2007).
- "Detailed Guide: Prostate Cancer Radiation Therapy." From the American Cancer Society's website. Available: http://www.cancer.org/docroot/CRI/content/CRI_2_4_4X_Radiation_Therapy_36.asp (Accessed July 29, 2007).