Radiation therapy for childhood brain and spinal cord tumours

Radiation therapy uses high-energy rays or particles to destroy cancer cells.

Many children with brain or spinal cord tumours have radiation therapy. The healthcare team will consider your child’s personal needs to plan the type and amount of radiation, and when and how it is given. Your child may also receive other treatments.

In children younger than 3 years of age, radiation can damage developing brain cells. Doctors will try to avoid or postpone radiation therapy until the child is older because it can affect the normal growth and development of a child’s brain. This can lead to long-term effects, such as learning and physical problems. Chemotherapy may be given to very young children until they reach the age of 3, at which time radiation can be given if it is still needed.

Radiation therapy may be used:

• to destroy cancer cells left behind after surgery
• as part of the main treatment to destroy the cancer cells if surgery is not an option
• to prevent or relieve symptoms from a tumour
• to try to lower the risk of a brain tumour coming back

Radiation therapy and chemotherapy may be given during the same time period to treat childhood brain and spinal cord tumours. This is called chemoradiation. Some chemotherapy drugs can help make radiation work better by making cancer cells more sensitive to radiation. Combining chemotherapy and radiation therapy can be more effective than either treatment on its own.

The following types of radiation therapy are most commonly used to treat childhood brain and spinal cord tumours.

During external radiation therapy, a machine directs radiation through the skin to the tumour and some of the tissue around it. External radiation therapy is also called external beam radiation therapy.

Your child's head needs to be kept as still as possible during radiation therapy treatment. The healthcare team may make a plastic mesh mask for your child to keep them from moving during treatment. Young children may need a general anesthetic or sedation before radiation therapy to help them keep still.

Radiation therapy is usually given in small daily doses (called fractions) over a 4-to-6-week period.

The radiation therapy team will base the size of the treatment area on the size of the tumour. They may use the following external radiation techniques to accurately target the area to be treated and spare as much surrounding normal tissue as possible.

3D conformal radiation therapy (3D-CRT) directs many beams of radiation at the tumour. The radiation oncologist uses a CT scan or an MRI to map the exact location and shape of the tumour. The radiation beams are then shaped and aimed at the tumour from different directions to treat the tumour from all angles. Each individual beam is fairly weak and less likely to damage normal tissue. A higher dose of radiation is delivered where the beams meet at the tumour.

Intensity-modulated radiation therapy (IMRT) is similar to 3D-CRT in that it delivers radiation from many different angles to treat the entire tumour. In addition to shaping and aiming the radiation beams, IMRT allows the radiation oncologist to adjust the strength, or intensity, of the individual beams. This reduces the dose of radiation reaching nearby normal tissue while allowing a higher dose to be delivered to the tumour. It is useful for treating tumours in hard-to-reach areas of the brain or spinal cord.

Volumetric-modulated arc therapy (VMAT) is an advanced form of IMRT that delivers a dose to the entire tumour in a 360-degree rotation. Most modern linear accelerators can deliver this type of treatment. This may shorten the daily treatment time.

Proton therapy may also be called proton beam therapy. It uses proton beams instead of x-ray beams. Protons release more energy after reaching a certain distance and then stop, while x-ray beams release energy before and after they hit their target. So, protons cause less damage to tissues they pass through before reaching their target. Proton therapy causes the least amount of damage to nearby normal tissues. A machine called a synchrotron or cyclotron produces the protons. These machines are not available in Canada, and your child may have to go to certain centres in the US to receive this treatment.

Stereotactic radiation therapy delivers external radiation therapy in very precise amounts to the tumour area. A CT scan or an MRI is used to create 3D pictures of the tumour and the surrounding normal brain tissue. This information is used to plan where the radiation will be directed (called the treatment field). A specialized computer program guides the delivery of radiation to the tumour. There are 2 types of stereotactic radiation therapy – stereotactic radiosurgery and stereotactic radiotherapy.

Stereotactic radiosurgery (SRS) delivers a single high dose of radiation to the tumour (called a single fraction). This treatment doesn’t involve surgery – no cut (incision) is made and tissue is not surgically removed. SRS may be used for small tumours. It is also sometimes used for small tumours that have already received radiation therapy.

Stereotactic radiotherapy (SRT) is similar to SRS, but it gives smaller doses of radiation over a number of treatment sessions (called fractions) until the total dose is given. This is also called fractionated radiosurgery.

Stereotactic radiation therapy can be given in 2 ways. The Gamma Knife uses radiation beams aimed at the tumour from hundreds of different angles for a short period of time. Each beam alone is weak, but a higher dose of radiation is delivered where the beams meet at the tumour. Stereotactic radiation therapy can also be given using a linear accelerator (LINAC) that is controlled by a computer. This machine moves around the brain or spinal cord to deliver radiation to the tumour from different angles. X-Knife, CyberKnife and Clinac work this way.

Brachytherapy is a type of internal radiation therapy. A sealed container of a radioactive substance, called an implant, is placed right into the tumour or in the area where the tumour was removed. The radiation kills cancer cells over time.

Brachytherapy is most often used along with external radiation therapy to treat childhood brain and spinal cord tumours. It provides a high dose of radiation at the tumour site, while the external radiation treats nearby areas with a lower dose.

For brain and spinal cord tumours, brachytherapy may be given as interstitial radiation. Interstitial radiation is a treatment in which thin radioactive tubes are put directly into the tumour and surrounding tissue.

Some tumours, such as ependymomas or medulloblastomas, can spread to the meninges, to the spinal cord or into the cerebrospinal fluid (CSF). If a child has a tumour that has a high risk of spreading to these areas, radiation must be given to the whole brain and the entire spinal cord. This is called craniospinal radiation. It is used, even if the entire tumour was removed, to lower the risk that the tumour will come back (recur).

During radiation therapy, the healthcare team protects healthy cells in the treatment area as much as possible. Side effects of radiation therapy will depend mainly on the type of radiation therapy, the size of the area being treated, the specific area or organs being treated, the total dose of radiation and the treatment schedule.

Tell the healthcare team if your child has any side effects that you think are from radiation therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help your child.

These are common side effects of radiation therapy used for childhood brain and spinal cord tumours:

• fatigue
• nausea and vomiting
• skin reactions
• headache
• hair loss
• excessive sleepiness (somnolence syndrome)
• dry mouth
• sore mouth

Other side effects can develop months or years after treatment for childhood brain and spinal cord tumours. Find out more about late effects of treatments for childhood brain and spinal cord tumours.

Find out more about radiation therapy and side effects of radiation therapy. To make the decisions that are right for your child, ask the healthcare team questions about radiation therapy.