Brain Tumors: Radiation Therapy

What is radiation therapy?

Radiation therapy uses energy to kill cancer cells. It helps control the growth of some types of brain tumors. In some cases, it can shrink the tumor fully. It’s often used with surgery or chemotherapy to treat a brain tumor. This type of treatment is done by a doctor called a radiation oncologist.

When might radiation therapy be used?

Radiation therapy may be used:

  • After surgery and sometimes with chemotherapy to try to kill remaining tumor cells in the brain

  • As the main (primary) treatment for the brain tumor, if surgery can’t be done

  • To help relieve symptoms caused by a brain tumor

Types of radiation therapy

There are 2 main types of therapy. Your doctor may give you both types. They include:

  • External beam radiation therapy (EBRT). For this type, a machine directs the rays of energy to the area of cancer. This treatment is usually done every weekday over several weeks.

  • Internal radiation (brachytherapy). This is also called interstitial therapy. Small pellets with radiation are placed inside or near the area with cancer.

External beam radiation therapy (EBRT)

There are several types of EBRT. These can target the tumor more closely. This can limit the effect that radiation has on other nearby healthy brain cells. Radiation can harm normal brain cells. To limit the harm, your doctor may use types of EBRT such as:

  • 3-D conformal therapy (3DCRT). For this treatment, imaging scans are used to match the radiation beams to the shape of the tumor from different angles. The scans may be done with computed tomography (CT). Or they may be done with magnetic resonance imaging (MRI).

  • Intensity modulated radiation therapy (IMRT).This is a similar method that lets the doctor control the intensity of the radiation beams pointed at different parts of the tumor.

  • Conformal proton beam therapy. This is similar to IMRT. It focuses beams charged particles called protons instead of X-rays on the tumor. Protons may be able to be focused more accurately. They may also stop more quickly than X-rays after hitting a target. This may lead to fewer side effects.

  • Stereotactic radiosurgery (SRS). This method can be used on small tumors. A high-energy dose of radiation is sent to the tumor from many angles. This type of treatment is given as a single dose. Or it may be given as several doses over a few days. Your doctor may use SRS as the main treatment or as an additional treatment. There are 2 types of SRS:

    • Gamma knife radiation. This uses radiation beams called gamma rays. The rays are sent from a machine and focused at the tumor from hundreds of angles at the same time. This treatment is usually done in 1 session.

    • Linear accelerator based. Instead of sending many beams at once, this machine moves around the head to send radiation to the tumor from different angles. Treatment is usually done in 1 to 5 sessions.

You'll have imaging tests to see if the cancer has spread to other parts of your brain and your spinal cord. If the cancer has spread, you may have radiation to your whole brain and spinal cord.


For this treatment, the radiation is placed very close to or inside the tumor. This may done with tiny plastic tubes, a balloon, or a fixed X-ray device. The radiation they give off travels a very short distance. This helps make sure it does not affect much nearby healthy tissue. This method may be used to send a high dose of radiation at the tumor site.

Possible side effects

Radiation treatment affects normal cells as well as cancer cells. It may cause side effects. These depend on how much radiation you get and how it's given. Possible side effects include:

  • Headache

  • Brain swelling (edema)

  • Skin irritation

  • Intolerance of cold

  • Nausea and vomiting

  • Tiredness

  • Trouble thinking and remembering

  • Side effects to the area treated, such as hearing loss

  • Problems with your thyroid, hypothalamus, or pituitary glands, which can affect hormone levels in your body

Radiation necrosis

In some cases, dead brain tissue will form at the site of the radiation. This is called radiation necrosis. The mass of dead brain tissue usually has both cancer cells and healthy cells. Radiation necrosis can take anywhere from months to years to develop.

Radiation necrosis may need to be removed with surgery if it causes problems such as:

  • Dementia

  • Headache

  • Seizures

It's not always easy to tell the difference between radiation necrosis and cancer that has come back. A brain scan called a positron-emission tomography (PET) scan can sometimes tell the difference. But often a biopsy is the only way to tell for sure.

Risk of future cancer

Radiation can also affect your genes. As a result, you have a small risk of a second cancer after radiation. This second cancer usually occurs many years later. Talk to your radiation oncologist about the risks and benefits of radiation therapy.

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Herold, David M., MD
Date Last Reviewed: 1/1/2018
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