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Stereotactic Radiosurgery

Stereotactic radiosurgery is a non-invasive procedure performed on an outpatient basis. This technology delivers radiation to a tumor, while effectively sparing the surrounding tissues and nerves. Radiosurgery is not surgery in the conventional sense, as no opening is made in the skull. Radiosurgery describes the use of intense radiation delivered to a tumor. It may be used instead of, or in addition to, conventional surgery. In certain cases, it may offer similar benefit and lower risk or discomfort than conventional surgery. Patients can avoid both hospitalization and anesthesia.

Stereotactic radiosurgery is performed using highly advanced computers to locate and create a three-dimensional image of a tumor. Stereotaxy adds depth to imaging, where conventional x-rays can only measure height and width. This enhances the neurosurgeon?s ability to precisely map the location of the tumor and find the best and safest pathway to removing it. Stereotactic techniques may be used to prepare for a surgery, during biopsy or tumor removal, while implanting radiation pellets, or to provide a navigation system during surgery. These techniques are especially useful in locating and radiating tumors deep within the brain, such as brain stem and thalamic tumors.

Although developed originally for use in the brain or other intracranial targets, stereotactic radiosurgery is rapidly becoming recognized as a useful treatment technique for tumors and vascular malformations of the spine and spinal cord as well.

  • Radiosurgery is a term describing precise localization and delivery of radiation to an intracranial target. Originally, it was used by neurosurgeons to produce tiny, circumscribed, non-invasive lesions in the brain for movement disorders and pain.
  • Stereotaxis refers to the precise localization of an anatomic target in 3-dimensional space, and radiosurgery is a term that now describes any precise, tightly circumscribed delivery of radiation, usually as a high dose in a single fraction, to a defined anatomic target. Multiple fractions may be used, a procedure termed stereotactic radiotherapy.
  • Together, they are an important means of treating both benign and malignant tumors as well as vascular malformations located near critical radiosensitive structures, such as optic nerve or spinal cord. Utilization of this treatment technique outside the head has been quite limited so far, but many of the technological hurdles are being overcome, and the future of stereotactic spinal radiosurgery is rapidly approaching.
  • Most spinal stereotactic radiosurgery utilizes a linear accelerator (LINAC) as the radiation source. Used stereotactically, this device employs multiple intersecting radiation arcs that produce a roughly spherical dose distribution, or isocenter. Multiple isocenters can be combined to shape a dose field to roughly match the shape of a target.
  • Stereotactic radiosurgical planning software topographically contours the prescription (or treatment) isodose level conforming to the targeted tissue while allowing the neurosurgeon and radiation oncologist to exclude nearby structures, such as spinal cord from high doses of radiation.
Some stereotactic techniques use a head frame and others do not.

Frame-Based Stereotactic Radiosurgery

With frame-based stereotactic surgery, a lightweight frame is attached to the skull at four points. Local anesthesia is used to numb the places where the pins contact the skull. Once the frame is attached a CT, MRI or dye scan (angiography) is done. Since the scan images both the tumor and the frame, it is able to show the exact location of the tumor in three dimensions in relation to the head frame. The neurosurgeon takes these coordinates and precisely inserts a probe through a small incision in the skull to perform the biopsy or other procedure.

It also has some limitations. The frame can sometimes obstruct the neurosurgeon?s view of the site; it can be time-consuming to manually set the frame and read the scans; there is a limited space to work within the radius of the arc; and the scans and surgery usually need to be performed the same day.

Frameless Stereotactic Radiosurgery

Instead of using an external frame as a reference point, frameless stereotactic surgery uses tiny markers, called fiducial markers, that are taped or glued to the head before the brain is scanned. The scan is then loaded into a planning and navigation computer, producing a 3-dimensional representation of the head, brain and tumor. During surgery these markers are touched with a pointing device, called a "wand." Identified on the scan, the computer "knows" where the surgical instrument is during the procedure in relation to the brain and tumor.

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