MNSC: Patient Resources: Stereotactic Radiosurgery

Stereotactic Radiosurgery
Gamma Knife Surgery

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You have probably been referred to see a neurosurgeon because of a brain tumor, abnormal collection of blood vessels inside your head, hearing loss or facial pain. You may also have experienced weakness, vision problems, bleeding inside your head for which you went to the hospital. Perhaps a problem was found inside your head that was not known earlier because a scan of your head was taken for a different reason.
You may be wondering if there is a chance that everything will return to normal or whether stereotactic radiosurgery is very risky. These questions and concerns can be addressed by your neurosurgeon, who is a physician trained in the treatment of disorders of the nervous system.

He will ask a number of questions and then perform a neurological examination.

Following a review of any x-rays or other diagnostic tests you may have brought with you, additional tests may be ordered if further information is needed.

Finally, he will propose a course of treatment which may or may not involve stereotactic radiosurgery.

The decision regarding your care should be reached after discussion between you, your family and your neurosurgeon.

Stereotactic radiosurgery

There are two common methods used to deliver stereotactic radiosurgery. One method uses a linear accelerator to deliver focused converging beams of radiation to the target by means of x-rays. Another method uses the Gamma Knife to deliver 201 low-intensity gamma rays to the target by means of a Cobolt-60 source. The goal of both treatment delivery systems is to deliver a dose of radiation to the target with a very high degree of accuracy without adversely affecting the surrounding brain tissue. There are many similarities between the two systems, however there are also distinct differences. A thorough discussion with your neurosurgeon will help you determine which method may be used to treat your problem.

Definition

Stereotactic radiosurgery is a method of delivering a high concentrated dose of radiation precisely directed at the abnormality for the purpose of stopping the growth, eliminating the abnormality or relieving symptoms caused by the abnormality. Stereotactic radiosurgery is not surgery in the conventional sense as it does not require an operation whereby an incision is made.

The goal of stereotactic radiosurgery is to deliver enough radiation to destroy or stop the growth of a lesion previously defined by specialized imaging techniques without adversely affecting surrounding tissue.

Diagnosis

Usually by the time of the office visit with the neurosurgeon, you know that an abnormality is present. This will have shown up on a CT, MRI or angiogram. Your neurosurgeon will obtain from you and/or your family a medical history and perform a neurological examination. Additional tests may be necessary such as a visual field examination or perhaps blood tests. The neurosurgeon may request that you see another specialist such as an endocrinologist if you have a pituitary tumor. He will ask many questions to determine how to proceed with discussion regarding treatment options which may involve observation, surgery or stereotactic radiosurgery.

Treatment

Unlike conventional whole brain radiation whereby a person receives a small amount of radiation every day over several weeks and can be given only once in a person's life time, stereotactic radiosurgery may be repeated. You can receive stereotactic radiosurgery in addition to whole brain radiation. Successfully treated tumors stop growing and begin to shrink. AVMs slowly occlude and disappear as changes occur in blood vessel walls.

Stereotactic radiosurgery may be performed using a linear accelerator or a Gamma Knife. Although there are many similarities, there are several differences.

Stereotactic Radiosurgery using a Linear Accelerator

After a stereotactic frame is attached to the patient's head by pins, an MRI and CT are taken of the brain to determine the precise location of the tumor. If the patient has an AVM, an angiogram and CT are performed with the frame attached. Computer-guided dosimetry is specified to match the lesion. Lesions up to 3.5 centimeters in diameter may be treated. A cone that approximates the size of the lesion is placed in the collimator of the linear accelerator. Cones range in size from 12.5 mm to 40 mm.

The patient is placed in a supine (lying on back) position on the treatment couch of the linear accelerator. The head is secured to prevent movement while receiving treatment. Radiation is given to the lesion from different directions called arcs. A predetermined amount of radiation is delivered in an arc, then the treatment couch is rotated as is the collimator housing the cone and a predetermined amount of radiation is given. This sequence continues until the therapy is complete. The number of arcs used varies from 4 to 6 or more and takes approximately 30 minutes.

Stereotactic Radiosurgery using a Gamma Knife

After a stereotactic frame is attached to the patient's head using pins, an MRI and CT are taken of the brain to determine the precise location of the tumor. If the patient has an AVM, an angiogram and CT are performed with the frame attached. The Gamma Knife consists of a sphere containing 201 Cobolt-60 sources. These sources are positioned so that the beams are targeted to a point within a cavity in the instrument where the patient's head is placed and covered by a helmet which narrows the beams and shields the head from unwanted radiation. The radiation is controlled by the percentage of the 201 ports that are used, the number of exposures and the head position. Computer-guided dosimetry is specified to match the lesion. Different beam sizes are available by using different helmets with holes of various sizes. Lesions from 5 to 40 millimeters can be treated which takes about 30 minutes. By performing multiple exposures and by readjusting the helmet and head position, different lesion shapes can be achieved.

Recovery

Following stereotactic radiosurgery, bandaids are usually placed over the pin sites from the stereotactic frame which should be removed the following day. You may be observed for a specified time after your stereotactic radiosurgery before you go home or you may be kept in the hospital overnight for observation. Some people experience a minimally amount of tenderness surrounding the pin sites. Occasionally, swelling occurs around the pin sites. If swelling occurs, you should keep your head elevated and apply an ice pack to the area. A mild analgesic such as tylenol may be helpful. Usually you may return to your usual activities the following day if you are not bothered by swelling. If you perform heavy lifting, please check with your neurosurgeon about any limitations.

Follow-up

Usually, your neurosurgeon will want to see you in the office in one month after the procedure. Your pin sites will be checked to assure they are healing properly. A neurological examination will be performed. Usually the first CT or MRI will occur approximately six months after your procedure to check on the status of your lesion. Changes in reducing the size or destroying the lesion occur over time and may take from one to three years.

Role of the Neurosurgeon

If you are having problems pertaining to your brain, a neurosurgeon is the appropriate medical professional to direct your treatment. Although his or her primary concerns will be diagnosis, interpretation of tests results, matters pertaining to the stereotactic frame and stereotactic images, there will be most likely be other medical professionals involved in the treatment process, such as radiation oncologists, radiologists and other specialists such as a neurologist or neuro-oncologist.

Neurological surgery is the specialty concerned with the diagnosis and treatment of disorders of the nervous system. Neurosurgeons treat patients with problems related to the head, spinal cord or nerves. For example neurosurgeons treat patients with tumors or vascular malformations of the brain or spinal cord; patients who have a stroke or in danger of a stroke due to clogged arteries in the neck; patients with neck or back pain associated with a slipped disc, narrowing or bone spurs.

Neurosurgeons undergo six to eight years of rigorous training following medical school. After successfully completing this training, two years of medical practice and a written examination, neurosurgeons can become Board Certified.