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Conventional radiation of most tumors involves multiple doses of radiation delivered over three to six weeks. Stereotactic radiation therapy, which is sometimes referred to as "radiosurgery," does not involve surgery. Instead, this is a technique based on the principle that a single relatively high dose of radiation delivered precisely to a small area will often arrest the tumor, while minimizing injury to surrounding nerves and brain tissue and/or function.
The source of the radiation used in radiosurgery is from either radioactive cobalt or a linear accelerator. The radiation is called a gamma ray when it comes from a cobalt source (such as the Gamma Knife Unit) and an x-ray when it comes from a linear accelerator (LINAC).
Radiation, even at relatively high doses such as those used in radiosurgery, does not kill or injure cells immediately. Following radiation, some tumor cells die in a matter of weeks, but others die more gradually, generally six to eighteen months after treatment. This treatment often arrests the growth of the tumor and some tumors will shrink, but the tumor does not disappear.
Follow-up studies are important because some tumors will continue to grow after this treatment or at some time in the future. A tumor which has been irradiated and grows may be more difficult to remove than an unradiated tumor. The possible cancerous effects of radiating an acoustic tumor have not been fully defined. And there are published reports of typical acoustic tumors becoming malignant following radiation treatment
Symptoms such as dizziness and disturbances of balance are improved earlier after microsurgical treatment than after radiation treatment because the effects of radiation treatment may require up to eighteen months. Many patients have some residual dizziness and disturbed balance after either radiation or microsurgical treatment, but this is commonly less after microsurgical treatment.
In patients with useful hearing before radiation treatment, about 50% will still have useful hearing two years after irradiation. Among patients with normal facial movement and sensation before treatment, 10% will develop some degree of facial weakness or numbness that usually recovers in several months. These early statistics compare very favorably with microsurgical tumor removal.
Microsurgical removal remains the treatment of choice for acoustic neuromas. An experienced microsurgeon, operating on tumors in the radiosurgery size range, can produce results comparable to radiosurgery and the long-term tumor cure or control rate appears more certain with microsurgery.
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