Radiation therapy for childhood brain and spinal cord cancer
Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation therapy plays a large role in the treatment of many childhood brain and spinal cord tumours.
Radiation may be used:
- as the primary treatment to destroy cancer cells
- after surgery to destroy cancer cells left behind and reduce the risk of the cancer recurring (adjuvantadjuvantTreatment given in addition to the first-line therapy (the first or standard treatment) to help reduce the risk of a disease (such as cancer) coming back (recurring). radiation therapy)
- on the spinal cord to destroy cancer cells that may have spread from a tumour in the brain
The amount of radiation given during treatment, and when and how it is given, will be different for each child. A great deal of preparation is done to ensure the radiation will be given accurately and safely while avoiding emotional trauma to the child.
Whenever possible, radiation is not given to children under 3 years of age because it can affect the normal growth and development of the 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 can also cause problems in older children. For this reason, the radiation oncologist makes every attempt to direct as much of the radiation as possible at the tumour, while trying to spare surrounding tissue.
External beam radiation therapy
Childhood brain cancer is usually treated with external beam radiation therapy (EBRT). EBRT is like getting an x-ray although the dose of radiation is much higher. A machine directs radiation to the tumour and some of the surrounding tissue. Radiation therapy is usually given on week days and only takes a few minutes. Young children who have difficulty lying still may need to be put to sleep (sedated).
Modern radiation techniques allow doctors to target the area to be treated much more accurately, while sparing as much surrounding normal tissue as possible.
Three-dimensional conformal radiation therapy (3D-CRT)
In 3D-CRT, the radiation oncologist uses MRI images of the tumour to map the exact location and shape of the tumour. Several radiation beams are then shaped and aimed at the tumour from different directions in order to treat the tumour from all angles.
Intensity-modulated radiation therapy (IMRT)
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 (intensity) of the beams. This reduces the dose of radiation reaching sensitive areas of the brain, such as the optic nerve, the brain steam and the pituitary gland, while allowing the full dose to be given to the tumour.
Conformal proton beam radiation therapy
Proton beam radiation therapy is similar to 3D-CRT except proton beams are aimed at the tumour instead of x-ray beams. X-ray beams release energy before and after they hit their target. Proton beams are different because they release most of their energy after travelling a certain distance and cause very little damage to tissues that they pass through. As a result, more radiation can be delivered to the tumour.
Proton beam therapy is not commonly used to treat childhood brain and spinal tumours. The machines needed to make protons are expensive and this type of radiation therapy may not be available at all treatment centres.
Hyperfractionation is a schedule for giving external beam radiation therapy. It is a way of giving radiation therapy twice per day in smaller doses. This allows a higher total dose of radiation to be given to the tumour with fewer side effects. Studies are currently underway to determine the long-term effects of hyperfractionation.
Stereotactic radiosurgery is not surgery. Instead, it is a form of radiation therapy that delivers a large dose of radiation precisely to the tumour while sparing healthy brain tissue. This is usually done as a single treatment session, but may also be done multiple times.
This procedure is usually done under general anesthetic and involves placing a special frame (called a stereotactic frame) on the child's head. This frame is similar to the one used to take a stereotactic brain biopsy. A CT or MRI scan is done to find the exact location of the tumour. The frame helps to aim the radiation beams precisely at the tumour from many different angles for a short period of time. A linear accelerator (LINAC), Novalis, Gamma Knife or Cyberknife are different radiation machines that could be used to deliver stereotactic radiosurgery.
Whole-brain and spinal cord radiation therapy (craniospinal radiation)
If the doctor discovers that the child’s brain tumour has spread to the meninges or the spinal cord, radiation may be given to the whole brain and the entire spinal cord. Medulloblastomas and other PNETs are tumours that commonly spread to the spinal cord.
Brachytherapy is internal radiation therapy. Radioactive materials (radioactive isotopes), often called seeds, are placed right into, or very close to the tumour. Radioactive materials can also be placed in the area from where the tumour was removed. The radiation given off only travels a short distance. It only affects the tumour and delivers a high dose of radiation directly to the tumour area. Over time, the radiation will kill the cancer cells.
Brachytherapy is not commonly used to treat childhood brain and spinal cord cancer, but it may have a role in treatment when used together with external beam radiation therapy. It requires a great deal of time, skill and a specialized team. 3D-CRT and IMRT are more commonly used.