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Radiation therapy for childhood brain and spinal cord tumours
Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation therapy is commonly used to treat childhood brain and spinal cord tumours. 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.
Whenever possible, radiation is not given to children under 3 years old 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 is sometimes combined with chemotherapy to treat childhood brain and spinal cord tumours. The 2 treatments are given during the same time period to improve the effect of radiation.
Radiation therapy is given for different reasons. Your child may have radiation therapy:
- to destroy cancer cells left behind after surgery
- as part of the main treatment to destroy the cancer cells in the body if surgery is not an option
- to prevent or relieve symptoms from the tumour
The following types of radiation therapy are most commonly used to treat childhood brain and spinal cord tumours.
External beam radiation therapy
During external beam radiation therapy, a machine directs radiation through the skin to the tumour and some of the tissue around it. The radiation therapy team will base the size of the treatment area on the size of the tumour. Young children may be sedated before radiation therapy to keep them still during treatment. Radiation therapy is usually given in small daily doses (called fractions) over a 4–5 week period.
Doctors may use the following modern radiation techniques to accurately target the area to be treated and spare as much surrounding normal tissue as possible.
3-D conformal radiation therapy (3D-CRT) involves many beams of radiation directed 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.
Conformal proton beam radiation therapy is a new way of giving radiation. It isn’t available in many treatment centres. Currently there are no machines in Canada. Children requiring this treatment have to go to certain centres in the US. Conformal proton beam radiation therapy uses proton beams instead of x-ray beams. X-ray beams release energy before and after they hit their target. Protons only release energy after travelling a certain distance. As a result, protons cause less damage to tissues that they pass through before reaching their target. Conformal proton beam radiation therapy causes the least amount of damage to nearby normal tissues. It is useful for treating tumours in hard-to-reach areas.
Stereotactic radiation therapy
Stereotactic radiation therapy delivers external beam radiation therapy in very precise amounts to the tumour area. A CT scan or an MRI is used to create 3-D 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.
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.
There are 2 ways stereotactic radiation therapy can be given. The Gamma Knife uses radiation beams focused at the tumour from hundreds of different angles for a short period of time. Each beam alone is weak, but where they meet at the tumour it gives a higher dose of radiation. Other methods use a linear accelerator (LINAC) that is controlled by a computer. This machine moves around the head to deliver radiation to the tumour from different angles. X-Knife, CyberKnife and Clinac work this way.
Whole-brain and spinal cord radiation therapy (craniospinal radiation)
If the brain tumour has spread to the meninges or the spinal cord or into the cerebrospinal fluid (CSF), radiation may be given to the whole brain and the entire spinal cord. This is called craniospinal radiation. Some tumours such as medulloblastomas can spread this way and must be treated with craniospinal radiation even if the entire tumour was removed, to decrease the risk of recurrence.
Brachytherapy is internal radiation therapy. It uses a radioactive material called a radioactive isotope. It is placed right into the tumour or very close to it. Radioactive materials can also be placed in the area where the tumour was removed. The radiation kills the cancer cells over time. Brachytherapy is most often used along with external beam 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.
Side effects can happen with any type of treatment for childhood brain and spinal cord tumours, but every child’s experience is different. Some children have many side effects. Other children have few or none at all.
During radiation therapy, the healthcare team protects healthy cells in the treatment area as much as possible. But damage to healthy cells can happen and may cause side effects. If your child develops side effects, they can happen any time during, immediately after or a few days or weeks after radiation therapy. Sometimes late side effects develop months or years after radiation therapy. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent.
Side effects of radiation therapy will depend mainly on the size of the area being treated, the specific area being treated, the total dose of radiation and the treatment schedule. Some common side effects of radiation therapy used for childhood brain and spinal cord tumours are:
- nausea and vomiting
- skin reactions
- hair loss
- excessive sleepiness (somnolence syndrome)
- dry mouth
- sore mouth
- hormone problems
- growth problems
- learning problems
- radiation necrosis
- second cancers
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.
Tell the healthcare team if your child has these side effects or others you think might be from radiation therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help your child.