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External Beam Therapy

What is external beam therapy and how is it used?
External beam therapy (EBT) is a method for delivering a beam of high-energy x-rays to the location of the patient's tumor. The beam is generated outside the patient (usually by a linear accelerator, see below) and is targeted at the tumor site. These x-rays can destroy the cancer cells and careful treatment planning allows the surrounding normal tissues to be spared. No radioactive sources are placed inside the patient's body.

Who will be involved in this procedure?
Delivery of external beam therapy requires a treatment team, including a radiation oncologist, radiation physicist, dosimetrist and radiation therapist. The radiation oncologist is a physician who evaluates the patient and determines the appropriate therapy. He or she determines what area to treat and how much radiation to deliver. Together with the radiation physicist and the dosimetrist, the radiation oncologist determines what techniques to use to deliver the prescribed dose. The radiation therapists are specially trained technologists who deliver the daily treatments.

What equipment is used?
Radiation oncologists use a machine, called a “linear accelerator,” that creates high energy radiation to kill the cancer. Your radiation oncologist will determine the equipment and strength most suited to your treatment.

How is the treatment delivered?
The radiation therapist brings the patient into the treatment room and places him/her on the treatment couch of the linear accelerator in exactly the same position that was used for simulation using the same immobilization devices. The therapist carefully positions the patient using the alignment lasers and the marks that had been placed on the patient during simulation. The therapist goes outside the room and turns on the linear accelerator from outside. Beams from one or more directions may be used and the beam may be on for as long as several minutes for each field.

The treatment process can take 10 to 30 minutes each day and most of the time is often spent positioning the patient. While receiving treatment, the patient is continually monitored and communicated with to ensure their comfort.

Patients usually receive radiation treatments once a day, five days a week for a total of two to nine weeks. The patient's diagnosis determines the total duration of treatment. Occasionally, treatments are given twice a day.


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