External beam radiation therapy: How it works, what it treats and side effects

Radiation therapy is a common type of cancer treatment that uses high-energy beams to target and destroy cancer cells.

External beam radiation treatment (EBRT) is the main type of radiation therapy. It can be used alone to treat cancer or along with other therapies, such as surgery or chemotherapy.

Here, I’ll explain more about external beam radiation and answer common questions about this type of cancer treatment.

How does external beam radiation work?

Most external beam radiation uses focused, high-energy photon (X-ray) beams to attack cancer cells. The radiation is delivered into the body using a machine called a linear accelerator, or LINAC. 

External beam radiation is a local therapy. This means that it is given only to the part of the body where it’s directed. For example, if you have breast cancer, you will only get radiation in your breast and nearby at-risk areas.

Which types of cancer does external beam radiation treat?

External beam radiation is used to treat many different cancers, including

• Breast cancer
• Prostate cancer
• Head and neck cancers
• Lung cancer
• Brain tumors
• Colorectal cancer
• Cervical cancer
• Endometrial cancer
• Bladder cancer
• Kidney cancer
• Melanoma
• Lymphoma

How do I prepare for external beam radiation?

First, you’ll meet with your radiation oncologist and other members of your care team. They’ll go over your treatment plan and discuss the benefits and possible side effects of radiation therapy.

Simulation

After the initial visit with your doctors, you’ll have a radiation treatment planning appointment, known as simulation.

During the simulation, doctors will place you in the position you’ll need to be in for radiation. Once they determine the proper position, your radiation oncologist will perform a CT scan. This allows them to specifically target and map out where the radiation needs to go and identify healthy tissue and structures to protect during radiation. Information from other scans, such as an MRI or a PET-CT, is also used to map out where the radiation needs to go.

Simulation will take about an hour, depending on your treatment plan. You will not receive any treatment during the simulation.

In the days after the simulation, your radiation care team will work together to develop your radiation treatment plan.

Your doctor may ask you to prepare before radiation, depending on what part of your body is getting treated. For example, you may need to drink enough fluids to fill your bladder before radiation to the pelvis or avoid eating heavy meals before radiation to the abdomen. Your care team will let you know what preparation, if any, is needed.   

What happens during external beam radiation therapy?

When you arrive for treatment, you’ll first check in with the receptionist. Then, you’ll be taken to a changing room where you’ll change into a gown. A radiation therapist will take you to the radiation treatment room and position you on the radiation treatment table. Your care team will then take images and compare them to the images from the simulation to make sure everything is aligned appropriately.

Once you’re properly in position, the radiation will be delivered. The treatment machine generates high-energy beams and aims them at the area mapped out by your doctor. You’ll need to lie very still during this time.

You won’t feel the radiation while it’s being administered, and it does not hurt.     

How long does external beam radiation last?

Each visit will last about 30 minutes to an hour. This includes check-in and getting you positioned on the radiation table. The radiation itself is delivered for just a few minutes. But visit times can vary, depending on your treatment plan. Your doctor can tell you what to expect.

How long you need radiation treatment depends on the type of cancer and how it will be treated. Most treatments are daily, Monday through Friday, for several weeks. However, some patients only need one treatment, while others may need 20 to 35 treatments. Your doctor will give you your treatment timeline.

Radiation oncologists at UT MD Anderson have conducted clinical trials comparing longer radiation treatments to shorter radiation treatments. Our goal is to reduce the number of radiation treatments, so we can lessen disruptions to patients’ daily schedules. 

Can you be around people after external beam radiation?

Absolutely. You are not radioactive after external beam radiation therapy. You can be around the elderly, babies and pets. You will not cause them any harm.

What are the side effects of external beam radiation?

The side effects of radiation tend to build up slowly over the course of treatment.

The most common side effect of radiation treatment is fatigue. Other side effects depend on what part of the body receives radiation and how much radiation you receive. For example, you may have:

• Skin irritation or redness in the treated area
• Hair loss in the area receiving radiation
• Throat irritation when swallowing
• Diarrhea
• Frequent urination or discomfort while urinating

You will meet your doctor each week while you’re undergoing radiation treatment. They’ll check to see how the cancer is responding to treatment and answer any questions you have. They’ll also check to see how you’re feeling. Tell them if you’re having any side effects, so they can find ways to help you manage them and keep you as comfortable as possible. 

After your treatment ends, your care team will continue to have follow-up visits with you. These visits are important to monitor the cancer, ensure your side effects are getting better and watch for any long-term effects that may develop after radiation.

What are the different techniques to administer external beam radiation?

There are many different techniques used to deliver external beam radiation therapy.

3D conformal radiation therapy

This technique uses three-dimensional scans to determine the exact shape and size of the treatment target. The treatment target is the part of the body we treat with radiation. This may be the tumor or the area where it was removed, along with nearby areas at risk for containing microscopic cancer cells. The radiation beams conform to the size and shape of the target, which helps minimize side effects to healthy tissue.

Image-guided radiation therapy (IGRT)

IGRT uses imaging before and sometimes during treatment to confirm the position of the treatment target and help guide the radiation beam. This can improve accuracy and allow adjustments in how the patient is positioned and, when needed, treatment planning.

Intensity modulated radiation therapy (IMRT)

IMRT focuses multiple radiation beams of different intensities directly on the tumor to deliver a highly conformal dose while protecting surrounding normal tissue.

MR-Linac radiation therapy

MR-Linac radiation therapy combines the imaging precision of an MRI scanner with a linear accelerator. It provides high-resolution images of the tumor and nearby tissue in real time during treatment, which can improve precision and help protect nearby normal tissue.

Proton therapy

Unlike other types of external beam radiation techniques that use photon beams, proton therapy uses positively charged particles called protons. Protons can deliver their maximum amount of energy to the treatment target with a minimal exit dose. This can reduce radiation beyond the target, which may help spare nearby healthy tissue and reduce side effects.  

Stereotactic radiosurgery (SRS)

Despite its name, this technique is not actually surgery. Instead, stereotactic radiosurgery uses many highly focused radiation beams to treat tumors and other conditions in the brain, often in a single treatment or a small number of treatments.

Stereotactic body radiation therapy (SBRT)

SBRT precisely targets tumors with very high doses of radiation. It’s used against smaller tumors, often as a treatment for lung cancer, prostate cancer and kidney cancer. It can also treat other cancers that have spread to different parts of the body, or when surgery isn’t an option.

Stereotactic spine radiotherapy

This technique uses guidance from CT scans to deliver the highest possible dose to tumors on the spine.

Volumetric modulated arc therapy (VMAT)

VMAT is a form of IMRT in which multiple radiation beams of different intensities are directed at the tumor through a rotating radiation treatment machine.

The difference between external beam radiation and brachytherapy

People often ask about the difference between external beam radiation and brachytherapy. The difference is where the radiation comes from.

External beam radiation uses a machine outside the body to send radiation beams to the tumor.

Brachytherapy is not external beam radiation. It’s a type of internal radiation therapy. This means radioactive sources are placed in the body at or near the tumor site. These radioactive sources then deliver radiation to the tumor. The radioactive sources can be left in permanently to release radiation over time or inserted for several minutes, hours or days and removed afterward.

If external beam radiation therapy is part of your cancer treatment plan, your doctor and care team will work to determine which type is right for you. 

Karen Hoffman, M.D., is a radiation oncologist who specializes in treating patients with breast and genitourinary cancers.

Request an appointment at UT MD Anderson online or call 1-877-632-6789.