Brain and Spinal Cord Tumors in Children

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Treating Brain/CNS Tumors In Children TOPICS

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. Radiation therapy may be used in different situations:

  • 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, however, are usually not given radiation because of possible long-term side effects with brain development. Instead, their treatment relies mainly on surgery and chemotherapy. Radiation treatment can also cause some problems in older children. Radiation oncologists try very hard to deliver high doses of radiation to the tumor while limiting the radiation to normal surrounding brain areas as much as possible.

Types of radiation therapy

In most cases, 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. In most cases, the total dose of radiation is divided into daily fractions (usually given Monday through Friday) over several weeks. For each session, your child lies on a special table while a machine delivers the radiation from a precise angle. 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 need to be sedated 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.

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 converge at the tumor to give a higher dose of radiation there. Your child may be fitted with a plastic mold resembling a body cast to keep him or her in the same position so that the radiation can be aimed more accurately.

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 is related to 3D-CRT and uses a similar approach. But instead of using x-rays, it focuses proton beams on the tumor. Protons are positive parts of atoms. 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. Doctors can use this property to deliver more radiation to the tumor and do less damage to nearby normal tissues.

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

Stereotactic radiosurgery/stereotactic radiotherapy: This type of treatment delivers a large, precise radiation dose to the tumor area in a single session (radiosurgery) or in a few sessions (radiotherapy). (There is no actual surgery in this treatment.) 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 is not healthy enough for surgery.

First, a head frame is attached to the skull to help precisely aim the radiation beams. 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, 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. An example of such a machine is the Gamma Knife.

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 radiation to the tumor from many different angles. Several machines with names such as X-Knife, CyberKnife, and Clinac are used in this way for stereotactic radiosurgery.

Stereotactic radiosurgery typically delivers the whole radiation dose in a single session, though it may be repeated if needed. Sometimes doctors give the radiation in several treatments to deliver the same or a slightly higher dose. This is called fractionated radiosurgery or stereotactic radiotherapy.

Brachytherapy (internal radiotherapy): Unlike the external radiation approaches above, brachytherapy involves inserting radioactive material 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 find the tumor has spread along the covering of the spinal cord (meninges) or into the surrounding cerebrospinal fluid, then 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.

Effectiveness of radiation therapy

Up to one half of all medulloblastomas and virtually all germinomas are cured by radiation therapy. Unfortunately, radiation does not cure most other brain tumors. If there is a small amount of the tumor remaining after surgery, astrocytomas, oligodendrogliomas, and ependymomas can sometimes be controlled by radiation therapy, but usually are not cured.

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.

During the course of radiation therapy, some children may become irritable and tired. Nausea, vomiting, and headaches are possible but are uncommon. Spinal radiation can cause nausea and vomiting more often than brain radiation. Sometimes dexamethasone (Decadron), a cortisone-like drug, can help relieve these symptoms.

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.

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 symptoms 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.

The risk of these effects must be balanced against the risks of not using radiation and having less control of the tumor. If problems are seen after treatment, it is often 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 without causing as many 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, as early radiation therapy may be lifesaving in some cases. It is important that you talk with your child’s doctor about the risks and benefits of treatment.

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

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, or less likely a bone cancer in the skull. If this does occur, it is 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.

For more information on radiation therapy, see our document Understanding Radiation Therapy: A Guide for Patients and Families.

Last Medical Review: 03/22/2013
Last Revised: 01/31/2014