Radiation therapy for brain and spinal cord cancer
Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation may be used for brain and spinal cord cancer:
- as the primary treatment, when surgery cannot be done, to destroy cancer cells
- after surgery (adjuvant radiation therapy) to:
- treat tumours that could not be completely removed
- destroy cancer cells left behind
- reduce the risk of the cancer recurring
- to treat recurrent brain tumours
- to control the symptoms of advanced brain and spinal cord cancer (palliative radiation therapy)
The amount of radiation given during treatment, and when and how it is given, will be different for each person.
External beam radiation therapy
Brain and spinal cord cancer may be treated with external beam radiation therapy. A machine directs radiation to the tumour and some of the surrounding tissue.
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 computed tomography (CT) scan or magnetic resonance imaging (MRI) to map the exact location and shape of the tumour. Several radiation beams are then shaped and aimed at the tumour from different directions to treat the tumour from all angles.
Intensity-modulated radiation therapy (IMRT)
IMRT is a type of conformal radiation therapy. 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 stem 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, but it uses proton beams 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.
The machines needed to make protons are expensive and this type of radiation therapy may not be available at all treatment centres.
Stereotactic radiation therapy
Stereotactic radiation therapy delivers external beam radiation therapy in very precise amounts to the tumour and surrounding tissue. A CT scan and MRI are used to create 3-dimensional pictures of the tumour and the surrounding normal brain tissue. This information is used to plan the treatment field. A specialized computer program guides the delivery of the 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 incision is made and tissue is not surgically removed. SRS may be used for small tumours (less than 4 cm in diameter). It is also sometimes used for small tumours that have already received radiation therapy.
- Stereotactic radiotherapy (SRT) is like SRS, but it gives smaller doses of radiation over a number of treatment sessions (called multiple fractions), until the desired total dose is given.
Stereotactic radiation therapy may be given by a specially modified linear accelerator or by specialized equipment (CyberKnife or Gamma Knife).
Whole-brain and spinal cord radiation therapy (craniospinal radiation)
If the brain tumour has spread to the meninges or the spinal cord, radiation may be given to the whole brain and the entire spinal cord. Some tumours, such as medulloblastomas, tend to spread in this manner and may require craniospinal radiation therapy (CSI) more often than other types of tumours. CSI is sometimes given to prevent a tumour from spreading within the brain and spinal cord (called prophylactic CSI).
Treatment 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).
Adjuvant therapy is often given when doctors do not know for sure if any cancer cells remain in the body after the first-line therapy.
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