External beam radiation therapy (EBRT)

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on April 29, 2022.

External beam radiation therapy (EBRT) is the most commonly used form of radiation oncology treatment. It uses high-dose radiation to destroy cancerous cells or shrink tumors.

During an EBRT procedure, a machine directs external beams of radiation into cancerous areas inside your body with extreme precision. This method helps reduce damage to healthy tissues.

EBRT is designed and monitored by a radiation oncologist, a doctor who specializes in treating cancer with radiation.

Treatment is typically given daily, Monday through Friday, on an outpatient basis over the course of a number of weeks. However, treatment is tailored to the patient’s individual needs, so some may need to go more or less often.

Cancer Treatment Centers of America® (CTCA) is now City of Hope®, joining forces to expand patient access to personalized, comprehensive cancer care.

What is external beam radiation therapy?

Using a special X-ray machine called a linear accelerator, EBRT delivers high-energy rays to tumors. The machine delivers radiation from any angle and shapes radiation beams to the contour of the tumor. The machine moves around the body without touching the patient, aiming radiation at the cancer. Some types of focused EBRT target a tumor with higher, more precise doses of radiation, while reducing damage to healthy tissue and nearby organs. As a result, modern EBRT may help reduce the risk of side effects associated with traditional radiation treatment.

What should I expect during my EBRT? 

Every patient’s experience during EBRT varies depending on the type of cancer, the size and location of the tumor and the type of therapy being used. But there are some general rules and expectations most patients should consider. For instance:

  • You may be asked to change into a hospital gown for your therapy, so wear clothes that are easy to remove. If a hospital gown is not necessary, you still may be asked to expose the area being treated, so you should wear clothes that are loose-fitting and comfortable. Do not wear jewelry.
  • A mold of the part of the body that is being treated may be required to help keep you still during treatment. If you are undergoing radiation therapy to the head and neck area, you may be fitted for a mesh mask designed to keep your head from moving during treatment.
  • Your skin may be marked with dots to identify the treatment area. These dots should remain on your skin for the duration of your treatment. If a mold or mask is required, it will also be marked.
  • You will need to remain still during your treatment, which will only take a few minutes.
  • EBRT is painless.
  • Patients do not become radioactive during or after EBRT treatments.

How long does external beam radiation therapy last?

EBRT treatments are typically outpatient procedures. The length of your treatment depends on many factors, including your type and stage of cancer. EBRT may be administered over a period of  weeks. Patients typically receive treatment once a day for five days in a row, generally Monday through Friday. The actual treatments last only a few minutes, but each session requires time to set up equipment and ensure the patient is in the correct position for treatment.

Types of EBRT

 3-D conformal radiation

This radiation therapy technique allows doctors to sculpt radiation beams to the shape of a tumor and is typically used on tumors with irregular shapes or that lie close to healthy tissues and organs, and may limit radiation exposure to surrounding healthy tissue. 3-D conformal radiation also allows doctors to view tumors in three dimensions. Based on these images, the radiation beams are delivered to the tumor from several angles.

Intensity-modulated radiation therapy (IMRT)

With IMRT, advanced software plans a precise dose of radiation, based on tumor size, shape and location. A computer-controlled device delivers the radiation in sculpted doses that match the 3-D geometrical shape of the tumor, including concave and complex shapes. The intensity of radiation beams can be adjusted across the treatment area in fractioned, separate beams as precision accuracy. This means higher doses of radiation can be delivered than traditional radiation therapy methods, while reducing exposure to healthy tissues. Because of its greater degree of accuracy, IMRT may be a treatment option for patients who have reached the maximum allowable dose of conventional radiation therapy and have a recurrent tumor in the treated area.

Image-guided radiation therapy (IGRT)

Tumors can shift inside the body, because of breathing and other movement. Image guided radiation therapy (IGRT) may allow doctors to locate and track tumors at the time of treatment and deliver more precise radiation treatment. This technology also allows our radiation oncologists to make technical adjustments when a tumor moves outside of the planned treatment range. As a result, the radiation treatment is targeted to the tumor as much as possible, helping to limit radiation exposure to healthy tissue and reduce common radiation side effects.


TomoTherapy® combines a form of intensity modulated radiation therapy (IMRT), with the accuracy of computed tomography (CT) scanning technology, in one machine. With this technology, we sculpt radiation doses to match complex tumor shapes while avoiding sensitive structures. Using built-in CT scanning to confirm the shape and position of the tumor before each treatment, TomoTherapy may reduce radiation exposure to healthy tissues and organs. Before every treatment, scanning technology provides a 3D image of the treatment area, so the radiation beams can be targeted according to the size, shape and location of the tumor(s) on that specific day. The “slice therapy” approach treats tumors one layer at a time. Side effects are often reduced because less radiation reaches healthy tissues and organs. Some cancer patients who have reached their maximum tolerance dose of traditional radiation may be a candidate for TomoTherapy radiation.

Stereotactic radiation procedures

These procedures are designed to deliver precise, highly concentrated doses of radiation to small areas in the body, allowing our radiation oncologists to reduce exposure to surrounding healthy tissue and limit the number of treatment sessions required. We use two types of stereotactic procedures: stereotactic radiosurgery and stereotactic body radiation therapy.

  • Stereotactic radiosurgery (SRS) is a form of radiation therapy in which a high dose of radiation is delivered to a small area in the brain or head from many angles. Although it’s not technically surgery (because there are no incisions), the delivery of radiation is so precise that it’s referred to as radiosurgery.
  • Stereotactic body radiation therapy (SBRT) is similar to stereotactic radiosurgery, but it’s used in areas outside the brain, such as the lungs, spine and liver.

What types of cancer are treated with EBRT?

External beam radiation therapy is used to treat many cancer types, including some of the most common cancers.

  • Breast cancer: External beam radiation is the most common form of radiation used in the treatment of breast cancer. Depending on what type of breast surgery is performed and whether or not lymph nodes are involved, the breast chest wall or regional lymph nodes may be targeted. If a cancerous tumor was removed via breast-conserving surgery (BCS), doctors will conduct EBRT in the area where the tumor was removed, as well as to the entire breast. In cases where cancer is found in surrounding lymph nodes, they may also be treated with EBRT.
  • Lung cancer: EBRT is used to treat both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) and surrounding areas where the cancer has spread. Treatments usually take place every weekday for four to six weeks but may vary based on specific needs. The following EBRT techniques are used to target the treatment to cancerous lung areas (and may be used for other cancerous areas, too), while at the same time protecting healthy tissue:
    • SBRT is used in early-stage lung cancers and when surgery isn’t possible. It may also be used if cancer has spread to the liver or adrenal gland. During SBRT, targeted beams of high-dose radiation are delivered to the tumor from multiple angles.
    • Three-dimensional conformal radiation therapy (3D-CRT) provides a 3D model of a tumor’s exact location. Radiation beams are shaped to target the tumor from a variety of angles.
    • Intensity-modulated radiation therapy (IMRT) is often used in tumors that are near structures like the spinal cord. The radiation beams’ strength may be adjusted to limit damage to healthy tissues.
  • Prostate cancer: EBRT is used to target the prostate gland in early stages of prostate cancer, and when cancer has spread to the bone. IMRT is the most common form of EBRT used to treat prostate cancer. During IMRT, a computerized machine travels around the body while radiation targets the prostate from multiple angles. Some machines use scanners to take pictures of the prostate to increase the precision of radiation beams in a procedure called image-guided radiation therapy (IGRT).
  • Colorectal cancer: EBRT is the most common form of radiation therapy used in people who have colon or rectal cancer. The length of treatment depends on the patient, but may take anywhere from days to weeks. Forms of EBRT such as 3D-CRT, IMRT and SBRT are helpful if colorectal cancer has spread to the liver or lungs, and when surgery isn’t an option.
  • Melanoma: When it comes to treating melanoma, EBRT is the most common form of radiation used. Before treatment, a simulation is performed to take exact measurements of the location and size of the cancer. Treatment length varies with each patient.
  • Non-Hodgkin lymphoma (NHL): When radiation is used in the treatment of NHL, it’s most commonly delivered via EBRT. First, a simulation is performed to determine the radiation dosage plan and the best radiation beam angles to target the cancer. Typically, treatments are given daily from Monday to Friday over the course of a few weeks.
  • Uterine cancer: EBRT is commonly used to kill uterine cancer cells. Before treatment, the skin is marked with permanent ink and a mold of the pelvis is made so the patient’s body is in the same position for every treatment session. Typically, treatments are 20 minutes long and take place every weekday for four to five weeks. Uterine cancer is often treated with an internal form of radiation, called brachytherapy.
  • Leukemia: When leukemia has metastasized to the brain, spinal fluid, bone or testicles, EBRT may be used to treat those areas. Treatment duration varies per patient.

External beam radiation therapy side effects

Standard radiation therapy treatments may damage some healthy cells, often causing unpleasant side effects. The side effects of EBRT may vary depending on the length of treatment and the part of the body being treated. A common side effect for EBRT for all cancers is fatigue. All other side effects only occur near the site being treated. For example:

  • Skin changes in breast cancer patients
  • Nausea in pancreatic or stomach cancer patients
  • Hair loss in head cancer patients
  • Difficulty swallowing in head and neck cancer patients
  • Tenderness and inflammation at the site of treatment

City of Hope approach to managing the side effects of EBRT

At City of Hope, we understand that many patients do not realize how the side effects of cancer treatments may affect them. That’s why we take the time to educate patients—before, during and after treatment—about how their bodies will respond and provide an array of supportive care therapies designed to help them maintain their strength, stamina and quality of life. Evidence-informed therapies that may help manage the side effects of EBRT include:

Expert cancer care


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