Brain Cancer & Radiation Therapy
Radiation is used when the entire primary tumor cannot be surgically removed. Most malignant brain tumors are treated with external-beam radiation even if the entire primary tumor is surgically removed, because hidden tumor cells often remain in brain tissue.
The survival rate for patients with malignant tumors (e.g., anaplastic astrocytoma, glioblastoma multiforme) more than doubles with radiation therapy, and it can prolong life for patients with low-grade gliomas as well.
Radiation therapists use several different approaches to treat primary brain tumors, but external-beam radiation is the most common. Local radiation therapy techniques, including external focal, brachytherapy, and stereotactic radiosurgery, may be administered to selected patients.
There are various other radiation techniques, some of which are being used on an experimental basis. An assortment of technologies, as well as the use of medications and other compounds, can make tumor cells more sensitive to radiation.
External-beam Radiation to Treat Brain Cancer
External-beam radiation, the traditional form of radiation therapy, delivers radiation from outside the body. Therapy usually begins a couple of weeks after surgery and is typically repeated 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. Some benign tumors are treated with external-beam radiation to prevent recurrence, even if the entire primary tumor has been surgically removed. They also may be treated with radiation at the time of recurrence.
Stereotactic Radiosurgery to Treat Brain Cancer
Stereotactic radiosurgery delivers radiation to the tumor in a single dose and does not involve surgery, as the term may imply. In this procedure, a head frame supporting a CT or MRI scanner may be attached to the skull. With the aid of computer imaging, the radiologist is able to pinpoint the exact location of the tumor and aim the beam of radiation directly at it.
Some tumors, however, cannot be treated with the intense local radiation of radiosurgery. For example, tumors near the optic nerves are better treated with several small doses, because the optic nerves are especially sensitive to radiation. These tumors may be treated using stereotactic radiotherapy. Stereotactic radiotherapy involves applying many small doses of radiation, using the same imaging techniques used in stereotactic radiosurgery.
Newer stereotactic techniques usually do not involve the use of the head frame. Radiation often is delivered from several different directions, hitting the tumor at various angles. The advantage of using localized radiation is that the surrounding, healthy tissue is left undestroyed. This treatment may be used in addition to external-beam radiation, especially in cases of malignant gliomas and mestastases that are in deep or sensitive areas of the brain. Types of machines that are used to perform stereotactic radiosurgery include modified linear accelerators (LINAC; e.g., CyberKnife) and Gamma knife.
Linear accelerators (e.g., CyberKnife) involve using small doses of radiation over multiple sessions (called fractionated stereotactic radiotherapy). In this treatment, which allows larger tumors to be treated, the patient is positioned on a bed that can be moved, providing flexible positioning. Linear accelerators produce positively-charged atoms (called protons) in patterns that are matched to the size and shape of the tumor and used to destroy cancer cells.
The Gamma knife uses ioninzing beams of radiation (called gamma rays) that are sent from different angles and come together at a single point on the tumor. Each beam is low dosage; however, when they converge, the intensity and destructive power is high. This treatment is used to treat small tumors.
Brachytherapy to Treat Brain Cancer
Brachytherapy involves implanting capsules containing radioactive substances into the tumor to deliver localized radiation. It is frequently applied to treat recurrent disease in an area previously treated by external-beam radiation.
Advantages of this type of radiation therapy include sparing vital structures close to the tumor and a shorter length of treatment (i.e., hours to days instead of weeks).
Because loss of pituitary function can be a long-term side effect of radiation therapy, an endocrine evaluation is an important part of follow-up care for patients who have received radiation. Neuropsychological testing may also be done to evaluate whether a patient has incurred diminished intellectual activity resulting from brain tumor radiation.