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Radiation Therapy for Brain Tumors in Adults
Radiation therapy uses high-energy rays or small particles to kill cancer cells. It’s often part of the treatment for brain tumors and spinal cord tumors. This type of treatment is given by a doctor called a radiation oncologist.
Radiation therapy may be used in different situations, such as:
External radiation therapy
Most often, the radiation is focused on the tumor from a source outside the body. This is called external beam radiation therapy (EBRT). This type of radiation therapy is much like getting an x-ray, but the dose of radiation is much higher.
Before your treatments start, the radiation team will determine the correct angles for aiming the radiation beams and the proper dose of radiation. This planning session, called simulation, usually includes getting imaging tests such as CT or MRI scans.
Most often, radiation is given daily, usually Monday through Friday, over several weeks. But the schedule depends on the reason it’s being given, how it’s being given, and other factors.
At each treatment session, you lie on a special table while a machine delivers the radiation from precise angles. The treatment is not painful. Much of each treatment session is spent making sure you’re in the right place and that the radiation is aimed correctly. The actual treatment time is much shorter.
High doses of radiation therapy can damage normal brain tissue, so doctors try to deliver the radiation to the tumor while giving the lowest possible dose to normal surrounding brain areas. Several techniques can help doctors focus the radiation more precisely:
3D-CRT uses the results of imaging tests such as MRI and special computers to map the location of the tumor precisely. Several radiation beams are then shaped and aimed at the tumor from different directions. Each beam alone is fairly weak, which makes it less likely to damage normal tissues, but the beams converge at the tumor to give a higher dose of radiation there.
IMRT is a more advanced form of 3D-CRT. It uses a computer-driven machine that moves around you as it delivers radiation. Along with shaping the beams and aiming them at the tumor from several angles, the intensity (strength) of the beams can be adjusted to limit the dose reaching the most sensitive normal tissues near the tumor. This may let the doctor deliver a higher dose to the tumor. Many hospitals and cancer centers now use IMRT.
This newer technique is similar to IMRT. For this treatment, you lie on a table that passes through the machine delivering the radiation. The source of the radiation (the linear accelerator) rotates around the table in an arc, delivering the beams from different angles. A computer controls the intensity of the beams to help keep the radiation focused on the tumor.
It’s not yet clear if this approach results in better outcomes than IMRT, although it does allow the radiation to be given over less time in each treatment session.
This type of treatment delivers a large, precise radiation dose to the tumor area in a single session (SRS) or in a few sessions (SRT). There is no actual surgery in this treatment. It may be used for some tumors in parts of the brain or spinal cord that can’t be treated with surgery or when a person isn’t healthy enough for surgery.
In the past, a head frame was often attached to a person’s skull to help aim the radiation beams. But frameless techniques are now available that make this unnecessary. Sometimes a face mask is used to hold the head in place.
Once the exact location of the tumor is known from CT or MRI scans, radiation is focused at the tumor from many different angles. This can be done in 2 ways:
- Machines like Gamma Knife aim hundreds of thin radiation beams at the tumor from different angles for a short time. Each beam alone is weak, but they all converge at the tumor to give a higher dose of radiation.
- Machines such as CyberKnife, Linac, Zap-X, and ExacTrac use a single, computer-controlled beam from a movable linear accelerator (a machine that creates radiation). Instead of delivering many beams at once, the machine moves around the head to deliver a thin beam of radiation at the tumor from many different angles.
SRS typically delivers the whole radiation dose in a single session, though it may be repeated if needed. For SRT (sometimes called fractionated radiosurgery), doctors give the radiation in several treatments to deliver the same or a slightly higher dose.
For IGRT, an imaging test such as a CT or MRI scan is done just before each treatment to help better guide the radiation to its target.
IGRT is typically used along with some of the more precise techniques for delivering radiation described here. It is most useful when the radiation needs to be delivered very precisely, such as when a tumor is very close to vital structures.
Proton beam radiation therapy is different from standard radiation therapy because it uses a beam of protons instead of x-rays. A proton beam delivers radiation to the tumor by releasing its energy at a specific distance, causing less damage to the healthy tissue it passes through. This is unlike x-rays, which release energy both before and after they hit their target.
Proton beam therapy can be given using approaches like 3D-CRT or IMRT.
This approach may be more helpful for brain tumors that have distinct edges, such as chordomas, especially when they’re near vital structures. But it’s not clear if it is as useful for tumors that typically grow into or mix with normal brain tissue, such as astrocytomas or glioblastomas.
There are a limited number of proton beam centers in the United States at this time, but more are being built.
If tests like an MRI or lumbar puncture find a tumor has spread along the covering of the spinal cord (meninges) or into the surrounding cerebrospinal fluid (CSF), radiation may be given to the whole brain and spinal cord.
Some tumors such as ependymomas and medulloblastomas are more likely to spread this way and often require craniospinal radiation.
Brachytherapy (internal radiation therapy)
In brachytherapy, radioactive material is inserted directly into or near the tumor. This can be done during surgery to remove the brain tumor, or it might be an option if the tumor comes back after treatment.
An example of brachytherapy is GammaTile. These are small tiles made mainly of collagen with small radioactive “seeds” in them. They are placed in the lining of the space created when a brain tumor is removed. The radiation they give off travels only a short distance, so it’s not likely to affect other parts of the brain. Over time, the tiles are absorbed by the body, while the seeds lose their radioactivity and can be left in place.
A possible advantage of this approach is that it allows radiation to be given to the area right after surgery, instead of having to wait several weeks, which is often the case with external radiation. However, it also has limits, such as not being able to reach tumor cells farther from the original tumor.
Possible side effects of radiation therapy for brain tumors
Radiation can damage normal brain tissue, which can lead to side effects.
Side effects during or soon after treatment: Some people become irritable and tired during the course of radiation therapy. Nausea, vomiting, and headaches are also possible side effects but are uncommon. Sometimes dexamethasone (a corticosteroid) or other drugs can help relieve these symptoms. Some people might have hair loss in areas of the scalp that get radiation. Other side effects are also possible, depending on where the radiation is aimed.
Problems with thinking and memory: A person may lose some brain function if large areas of the brain get radiation. Problems can include memory loss, personality changes, and trouble concentrating. There may also be other symptoms, depending on the area of the brain treated and how much radiation was given. These risks must be balanced against the risks of not using radiation and having less control of the tumor.
Radiation necrosis: Rarely after radiation therapy, a mass of dead tissue (necrosis) can form at or near the site where the tumor was treated. This may happen months or even years after treatment and can cause swelling and pressure on nearby healthy brain tissue. The swelling can often be controlled with corticosteroid drugs, but sometimes surgery is needed to remove the necrotic tissue.
Increased risk of another tumor: Radiation can damage genes in normal cells. As a result, there is a small risk of developing a second cancer in an area that got radiation — for example, a meningioma of the coverings of the brain, another brain tumor, or less likely a bone cancer in the skull. If this happens, it's usually many years after the radiation is given. This small risk does not outweigh the benefits of radiation for those who need it.
More information about radiation therapy
To learn more about how radiation is used to treat cancer, see Radiation Therapy.
To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: January 5, 2026
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