Radiation Therapy & Nervous System Tumors
Most malignant brain tumors are treated with external-beam radiation even if the entire primary tumor is surgically removed, because often there are hidden tumor cells still left in the brain tissue.
For benign tumors, radiation is usually applied when the entire primary tumor cannot be surgically removed.
For malignant tumors, radiation more than doubles the survival rate for patients with anaplastic astrocytomas and glioblasoma multiformes, and it can prolong survival for patients with low-grade gliomas.
External Beam Radiation
External beam radiation is the traditional form of radiation therapy. It delivers radiation from outside of the body, usually a couple of weeks following surgery. It is typically applied at regular intervals for several weeks.
Hyperfractionation is a modified form of external beam radiation that involves applying less intense but more frequent doses of radiation, to which some patients respond more readily.
Newer types of radiation that are being used to treat brain tumors include stereotactic radiosurgery or radiotherapy, as well as brachytherapy. Stereotactic radiosurgery involves using focused radiation on a localized spot in a single dose. Even though it is called "radiosurgery," it does not involve actual surgery. A head frame, to which a CT or MRI scanner is attached, is attached to the patient's skull, and with the aid of the computer imaging, the radiologist is able to pinpoint the tumor and aim the radiation directly at it.
There are new stereotactic techniques that do not involve the use of the head frame. Often the radiation comes from several different directions and hits the tumor at various angles. The advantage of such localized radiation is that the surrounding, healthy tissue is left undestroyed.
It is often used in addition to external beam radiation, especially for malignant gliomas and mestastases that are in deep or sensitive areas of the brain where surgical removal is potentially dangerous. Some tumors, however, cannot be treated with such intense local radiation. The optic nerves are especially sensitive to radiation, so tumors near the optic nerves are better treated with several small doses rather than one big blast.
Stereotactic radiotherapy involves applying many small doses of radiation to a local spot, using the same imaging techniques that stereotactic radiosurgery requires. Brachytherapy involves implanting capsules that contain radioactive substances into the tumor.
There are various other radiation techniques, some of which are being used on an experimental basis. Other technologies include the use of medications or other compounds that may make tumor cells more sensitive to radiation.