What Is External Beam Radiotherapy?

Jacquelyn Gilchrist

External beam radiotherapy, often called external beam radiation therapy, is a treatment method for cancer that uses focused radiation to shrink tumors. A machine called a linear accelerator delivers the x-rays directly to the tumor site, and avoids sending radiation to the surrounding, healthy tissues. External beam radiotherapy may also be used prior to the surgical removal of a tumor, to prevent the regrowth of a tumor, and to ease symptoms in patients with advanced, metastasized cancer that is not believed to be treatable. This type of cancer treatment is generally appropriate for patients with cancers of the breast, lung, and prostate, as well as the brain, bowels, and head or neck.

A linear accelerator can be used for external beam radiography to target cancer cells with radiation.
A linear accelerator can be used for external beam radiography to target cancer cells with radiation.

Prior to receiving external beam radiotherapy, the patient will undergo a simulation of the treatment with a radiation therapist. Temporary ink or permanent tattoos will be used to mark the area of the body that will be treated. The therapist will then place the patient in the correct position on the scanner to allow the beam of radiation to focus directly on the tumor. He may provide the patient with pads, a body mold, or other objects to aid the patient in remaining completely still in that position. Once the correct position has been determined, alignment lasers and imaging will record it for later use.

For the actual external beam radiotherapy session, most patients will be asked to change into a hospital gown. Depending on where the radiation is focused, some people may need to wear a special mask over their faces. After the patient is positioned on the scanner, the technician will go into an adjacent observation room to operate the equipment.

Most patients will receive external beam radiotherapy once daily, five days a week, for approximately two to 10 weeks. Some patients may benefit from smaller doses of radiation given twice daily. Each session will take no longer than 30 to 60 minutes, although the radiation is only emitted for a handful of minutes. For the majority of the session, the radiation therapist will work to ensure the patient is in the correct position so that the radiation does not focus on the wrong area of the body.

During the external beam radiotherapy treatment, patients will not feel pain, but they may see colored lights and hear buzzing noises. The machine may also emit a faint smell, but this is not a cause for alarm. This type of cancer treatment does have potential side effects, such as fatigue, urinary changes, and bowel changes. Since external beam radiotherapy targets the tumor specifically, rather than the healthy tissue, the potential for side effects tends to be greatly reduced compared to other types of cancer treatments.

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