Radiation Therapy for Brain and Spinal Cord Tumors in Children

Radiation therapy uses high-energy x-rays or small particles to kill cancer cells. This type of treatment is given by a doctor called a radiation oncologist.

When might radiation therapy be used?

Radiation therapy may be used in different situations for brain or spinal cord tumors:

• After surgery to try to kill any remaining tumor cells
• As part of the main treatment if surgery is not a good option
• To help prevent or relieve symptoms from the tumor

Children younger than 3 years are usually not given radiation because of possible long-term side effects with brain development. Instead, they are treated mainly with surgery and chemotherapy. Radiation can also cause some problems in older children. Radiation oncologists try very hard to deliver enough radiation to the tumor while limiting the radiation to normal surrounding brain areas as much as possible.

Getting 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).

Before your child’s treatments start, the radiation team will take careful measurements to 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.Your child might be fitted with a plastic mold like a body cast to keep them in the same position so that the radiation can be aimed more accurately.

Most often, the total dose of radiation is divided into daily fractions (usually given Monday through Friday) over several weeks. For each treatment session, your child lies on a special table while a machine delivers the radiation from precise angles. Each treatment is much like getting an x-ray, but the dose of radiation is much higher. It is not painful. Some younger children might be given medicine to make them sleepy to make sure they don’t move during the treatment. Each session lasts about 15 to 30 minutes, but most of the time is spent making sure the radiation is aimed correctly. The actual treatment time each day is much shorter.

Special radiation therapy techniques

Radiation therapy can damage normal brain tissue, so doctors try to deliver high doses of radiation to the tumor with the lowest possible dose to normal surrounding brain areas. Several techniques can help doctors focus the radiation more precisely:

Three-dimensional conformal radiation therapy (3D-CRT): 3D-CRT uses the results of imaging tests such as MRI and special computers to precisely map the location of the tumor. 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 join together at the tumor to give a higher dose of radiation there.

Intensity modulated radiation therapy (IMRT): IMRT is an advanced form of 3D therapy. In addition to 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. This may let the doctor deliver a higher dose to the tumor. Many major hospitals and cancer centers now use IMRT.

Conformal proton beam radiation therapy: Proton beam therapy uses an approach similar to 3D-CRT. But instead of using x-rays, it focuses proton beams on the tumor. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and then release their energy after traveling a certain distance. This means that more radiation can be delivered to the tumor, while doing less damage to the normal tissue around it.

This approach may be more helpful for brain tumors that have distinct edges (such as chordomas), but it's not clear if it will be useful for tumors whose edges are mixed with normal brain tissue (such as astrocytomas or glioblastomas). There are only a limited number of proton beam centers in the United States at this time.

Stereotactic radiosurgery (SRS)/stereotactic radiotherapy (SRT): 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). It may be useful for some tumors in parts of the brain or spinal cord that can’t be treated with surgery or when a child isn’t healthy enough for surgery. (The term "radiosurgery" is used because the radiation is delivered so precisely, but there is no actual surgery involved in either SRS or SRT.)

For either procedure, a head frame is usually attached to the skull to help aim the radiation beams. Sometimes a face mask is used to hold the head in place instead. 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:

• In one approach, thin radiation beams are focused at the tumor from hundreds of different angles for a short period of time. Each beam alone is weak, but they all converge at the tumor to give a higher dose of radiation. The Gamma Knife is an example of a machine that uses this approach.
• Another approach uses a movable linear accelerator (a machine that creates radiation) that is controlled by a computer. Instead of delivering many beams at once, this machine moves around the head to deliver a thin beam of radiation to the tumor from many different angles. Several machines with names such as X-Knife, CyberKnife, and Clinac deliver stereotactic radiosurgery in this way.

SRS typically delivers the whole radiation dose in a single session, though it may be repeated if needed.

For SRT (also called fractionated radiosurgery) doctors give the radiation in several treatments to deliver the same or a slightly higher dose, which can now often be done without the need for a head frame.

Other types of radiation therapy

Brachytherapy (internal radiation therapy): Unlike the external radiation approaches above, in brachytherapy a radiation source is put directly into or near the tumor. The radiation it gives off travels a very short distance, so it affects only the tumor. This technique is most often used along with external radiation. It provides a high dose of radiation at the tumor site, while the external radiation treats nearby areas with a lower dose.

Whole brain and spinal cord radiation therapy (craniospinal radiation): If tests such as an MRI scan or lumbar puncture show the tumor has spread along the covering of the spinal cord (meninges) or into the surrounding cerebrospinal fluid, then external 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 therefore may require craniospinal radiation.

Possible effects of radiation therapy

Radiation is more harmful to tumor cells than it is to normal cells. Still, radiation can also damage normal brain tissue, especially in children younger than 3 years, which can lead to side effects.

Side effects during or soon after treatment: During radiation therapy, some children may become irritable and tired. Nausea, vomiting, and headaches are also possible but are uncommon. Spinal radiation causes nausea and vomiting more often than brain radiation. Sometimes dexamethasone (a corticosteroid) or other drugs can help relieve these symptoms. Some children might have hair loss in areas of the scalp that get radiation.

Some weeks after radiation therapy, children may become drowsy or have other nervous system symptoms. This is called the radiation somnolence syndrome or early-delayed radiation effect. It usually passes after a few weeks.

Problems with thinking and memory: Children may lose some brain function if large areas of the brain get radiation. Problems can include memory loss, personality changes, and trouble learning at school. These may get better over time, but some effects may be long-lasting.

Other side effects: Other effects could include seizures and slowed growth. There may also be other symptoms depending on the area of the brain treated and how much radiation was given.

Radiation necrosis: Rarely, a large mass of dead (necrotic) tissue forms at the site of the tumor in the months or years after radiation treatment. It can often be controlled with corticosteroid drugs, but surgery may be needed to remove the necrotic tissue in some instances.

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 the area that got the 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 occurs, it's usually many years after the radiation is given. This small risk should not keep children who need radiation from getting treatment. It’s important to continue close follow-up with your child’s doctor so that if problems do come up they can be found and treated as early as possible.

Balancing the risks and benefits

The risk of all of these side effects must be balanced against the risks of not using radiation and having less control of the tumor. If problems are seen after treatment, often it’s hard to determine whether they were caused by damage from the tumor itself, from surgery or radiation therapy, or from some combination of these. Doctors are constantly testing lower doses or different ways of giving radiation to see if they can be as effective while causing fewer problems.

Normal brain cells grow quickly in the first few years of life, making them very sensitive to radiation. Because of this, radiation therapy is often not used or is postponed in children younger than 3 years old to avoid damage that might affect brain development. This needs to be balanced with the risk of tumor regrowth, because early radiation therapy may be lifesaving in some cases. It’s important that you talk with your child’s doctor about the risks and benefits of treatment.