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Radiation therapy is a noninvasive procedure in which beams of radiation are targeted to the tumor to stop its growth while minimizing the risk of harming surrounding healthy tissue. This therapy differs from acoustic neuroma microsurgery in that there is no intention of curing the patient by removing or excising the tumor. Rather, the goal of radiation therapy is to control the growth of the tumor by destroying it with beams of high energy radiation which causes necrosis (tissue death). This type of therapy is usually reserved for small tumors, 3 cm. or less.

There are two modes of delivery of radiation to the patient with an acoustic neuroma:

• Stereotactic radiosurgery (Gamma knife)
• Fractionated stereotactic radiosurgery (FSR)

Stereotactic Radiosurgery

Stereotactic radiosurgery, also referred to as Gamma knife radiosurgery is a very precise type of radiation therapy that is used to treat a variety of tumors located in the brain. Although the term "radiosurgery" implies that this treatment is a type of surgical procedure, it's name actually derives from the "surgical" (pinpoint) precision that doctors can achieve with this technique by focusing x-rays directly to the area of a tumor. This highly sophisticated mode of radiation therapy involves several specialists, including a neurosurgeon and a radiation oncologist.

Stereotactic radiosurgery is typically performed under the following circumstances:

• Patients who are elderly (older than 65 years)
• Patients who cannot tolerate standard acoustic neuroma surgery
• Patients who previously underwent partial tumor resection
• Patients who refuse to undergo surgery for various reasons
• Deafness in the unaffected ear
• Presence of bilateral acoustic neuromas (both sides)

Gamma knife radiosurgery is a single-dose radiation treatment. It enables doctors to pinpoint abnormal tissue and deliver radiation with pinpoint accuracy. Radiation beams are merged from different locations outside of the head and merged into one beam at the target point. Accuracy is within a fraction of a millimeter. The source of radiation is typically either radioactive cobalt (gamma radiation) or a linear accelerator (LINAC). This type of treatment has been reported to have a high success rate of tumor control and a low incidence of facial weakness or numbness. Hearing preservation is equivalent to that following acoustic neuroma surgery. Stereotactic radiosurgery is contraindicated in cases where an acoustic neuroma is compressing the brainstem or cerebellum,.

Preparation for radiosurgery typically consists of not eating or drinking after midnight before the scheduled treatment. Patients are typically awake but may be sedated if they are anxious. The hair is usually pulled back but not shaven. At the time of the procedure, a local anesthetic is administered after which a special frame, similar to a halo, is attached to the head with 4 screws. These hold the head perfectly immobile so that the radiation beams converge and are delivered to a precise location. The frame is lightweight and once it is in place, imaging scans determine the exact location of the tumor. The patient then rests while calculations are performed regarding the dose of the radiation, the number of fields from which beams will be delivered, and the precise point where the beams will converge. During the actual treatment, the head is placed into a helmet which attaches to the head frame. The patient does not feel the radiation nor is there any noise during the treatment.