Radiosurgery (CyberKnife for Skull Base Tumors or Acoustic Neuromas)

Stereotactic Radiation (Radiosurgery) for Acoustic Neuroma Treatment

Overview

Stereotactic Radiation, also called radiosurgery, is a method of radiating tumors by using radiation from multiple different directions so that the radiation gets concentrated on the tumor and the surrounding brain receives less radiation. The 3 most common systems used for radiation delivery to acoustic neuromas are the Linear Accelerator, the GammaKnife, and the CyberKnife systems. The linear accelerator system (Varian) is an older system and is used uncommonly for acoustic neuromas.

Patients with small and medium sized tumors (less than 3 cm) in older patients (over 65) or any patient who has medical problems (such as heart disease, etc) that prevent undergoing surgery are the best candidates for radiation. Younger patients who desire, may also undergo stereotactic radiation. The radiation is given by one of several methods: Linear accelerator, Gamma Knife, or Cyberknife. Radiation therapy is effective in stopping the growth of 95% of tumors.

CyberKnife

The CyberKnife system is one of the most advanced forms of radiosurgery. It is a method of treating acoustic neuromas and other tumors using precisely targeted radiation. It uses a robotic arm to deliver the highly focused beam of radiation to the tumor with significantly less radiation to the surrounding normal brain. The specialists at the Division of Neurotology-Skull Base Surgery at UC Irvine is one of only a few centers in California that offer this service for acoustic neuromas. The radiotherapy is done with a team of experts in radiation therapy and radiation physics in Newport Beach. The team has over 10 years of experience with the CyberKnife system.

Compared to other radiosurgical treatments (such as GammaKnife), the CyberKnife offers several advantages to patients, including rapid relief from pain and other symptoms. Treatments are performed on an outpatient basis, with each treatment lasting between 60 to 90 minutes. The number of treatments vary depending on the tumor size, location and shape but typically only one to five daily sessions are required. During a CyberKnife treatment, the patients lie comfortably on the procedure table without anesthesia while the robotic arm moves, without touching them, to treat the tumor. The patients often recover immediately, given the low chance of complications and damage to healthy brain tissue.

GammaKnife

The gamma knife works by a process called stereotactic radiosurgery, which uses multiple beams of radiation converging in three dimensions to focus precisely on a small volume, such as a tumor, permitting intense doses of radiation to be delivered to that volume. The radiation is delivered by 201 sources that are in the device. The patient is placed under local anesthesia while a special headframe that has three-dimensional coordinates built into it is attached to the skull with four screws. Then, an MRI scan is obtained and the results are sent to the gamma knife's planning computer system. The surgeon will perform the planning and the patient is radiated. UC Irvine physicians are one of the first to perform radiosurgery using the new GammaKnife Perfection Device.

New Innovations in Radiosurgery

Fractionated stereotactic radiotherapy is a noninvasive treatment for tumors of the skull base. Fractionated stereotactic radiotherapy means that the radiation is given in multiple small doses (usually 3-5) rather than a single dose. Although fractionated stereotactic radiotherapy requires multiple irradiation sessions, recent reports have indicated that for small to medium tumors (smaller than 3 cm in diameter), it provides similar success to single treatment. The advantage of the fractionated method is that there is a smaller chance of risk to the facial nerve (the nerve that moves the face) and the trigeminal nerve (the nerve that supplies sensation to the face). In addition, fractionated stereotactic radiotherapy has a higher chance of preserving hearing in patients who have some hearing.

Fractionated stereotactic radiotherapy is easiest to perform with a CyberKnife system given that it does not require a frame to be secured to the patient's head using screws, as is required in the GammaKnife system. The CyberKnife system relies on a custom-built face mask to ensure there is no movement during treatment.

Above is an image of the computer-based planning for the radiation to concentrate on the tumor (red line) with minimal radiation to the surrounding brain. This patient's radiosurgery was divided into 5 sessions which helped preserve her hearing.

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