Radiosurgery is a surgical procedure where narrow beams of radiation are targeted to a precisely defined volume of tissue within the brain. This highly focused and destructive dose of radiation is given in a single session and avoids potentially harmful radiation to surrounding brain structures.   Professor Lars Leksell, a Swedish neurosurgeon, first developed stereotactic devices (used to guide the gamma rays)  as well as the very concept of radiosurgery in the early 1950’s. Together with Borje Larsson, a physicist, Leksell built the first Gamma Knife unit in Sweden in 1968. Since that time, this non-invasive technique for the treatment of brain tumors and vascular malformations has enjoyed incredible success. More than 60,000 patients have been safely treated with focused gamma rays world-wide.

Radiosurgery differs from conventional radiation therapy in several respects. With standard external beam radiation therapy techniques, tumors and much or all of the surrounding brain are treated to the same dose of radiation. The radiation dose is given in small increments over several weeks to allow normal brain tissue to recover from its effect, while tumor tissue is less likely to recover. Ultimately, the brain can absorb a maximal dose of radiation, beyond which no further treatment is advisable. There is increasing evidence that over long periods of time, high doses of radiation are harmful to normally functioning brain. The technique of Gamma Knife radiosurgery treats only the abnormal tissue, in a single session, without significant radiation to adjacent brain. Professor Leksell’s concept has proved to be a true advance in the treatment of intracranial disease.

Evaluation:

Radiosurgery is carried out through the cooperative efforts of a neurosurgeon, radiation oncologist and physicist. Your initial consultation will help you determine if GK radiosurgery is appropriate, effective and safe for your problem. Every patient should have information about all applicable treatments, the expected outcomes, risks, costs and the natural history of the untreated disease process. The decision of treatment is yours to make.

Frame Placement:

Early in the morning we fix a lightweight aluminum frame to the head using local anesthesia and intravenous, conscious sedation. This procedure is rapid and well tolerated. In fact, most patients have no recall of frame placement! The frame remains in place until the end of treatment later in the day.

Imaging:

After frame placement patients undergo CT or MR imaging. Patients with vascular abnormalities may undergo an angiogram. These images are used for treatment planning purposes. 

Treatment Planning:

The Gamma Knife contains 201 small Cobalt sources of gamma rays arrayed in a hemisphere within a thickly shielded structure. A primary collimator aims the radiation emitted by these sources to a common focal point. This is analogous to focusing the radiant energy of the sun with a magnifying glass to a hot focus. Near the glass there is not much heat, but the energy is intense at the focal point. Optical lenses can not focus gamma rays, rather individual beams are allowed to summate by overlapping at the focal point of the collimator, achieving the same effect. A second collimator, which fits within the primary collimator, allows the beam focus size to be adjusted from 4 to 18 mm in size.

Radiosurgery:

The computer software reduces the treatment plan to a list of simple instructions to guide the gamma rays to the target. The patient’s stereotactic head frame is fixed within the secondary collimator according to these instructions. Then the secondary collimator is merged with the primary collimator for treatment. Usually several shots are used to cover the entire target volume. Total treatment time varies from 45 minutes to 1 ½ hours. Following treatment, the frame is removed and patients are observed overnight or are discharged home.

After Care:

There are almost no initial effects of radiosurgery. A very few patients have experienced seizures; almost always these are individuals with established seizure disorders. Care is taken to adjust anticonvulsant levels prior to treatment to avoid this event. Local pain in the scalp responds to simple, oral pain medication. Long range effects after many months include swelling within the adjacent brain, which may cause symptoms such as headache and neurological disturbances. Almost always this swelling is treated with oral steroids and is self-limiting. Permanent cranial nerve dysfunction causing double vision, facial numbness, weakness, hearing loss, visual loss (depending on the site treated) is rare with modern gamma ray doses. Usually your neurosurgeon will follow treatment with MR/CT imaging every 3 months to every year to assure control of the tumor. Arteriovenous malformations may be followed by interval MR angiograms each year. These follow-up protocols vary from center to center.

The cure of a brain tumor by radiosurgery means that the tumor loses its ability to grow and remains the same size, never growing again. The intensely focused gamma rays destroy the ability of the cells to divide. Sometimes benign tumors actually shrink over time and malignant tumors may completely disappear. Arteriovenous malformations usually occlude after focused radiosurgery. This curative process occurs over months to years.

Following conventional, open surgery, the cure of a brain tumor usually requires the complete, physical removal of the abnormal tissue. Over time most malignant and some benign tumors recur. So continued imaging surveillance is also useful to ensure surgical cure.

Metastatic Brain Tumors:

Experience has shown that surgical removal of single brain metastases followed by radiation therapy to the brain benefits patient’s quality of life and survival when compared to treatment by brain radiotherapy alone. To achieve this benefit, usually there must be control of the patient’s primary tumor. Experience has also shown that Gamma Knife radiosurgery is as effective as open surgery in the control of metastatic brain tumors when combined with radiotherapy of the brain. This is being extended to the control of multiple brain metastases. In selected individuals we do not carry out whole brain radiotherapy following Gamma Knife radiosurgery. Usually we request close follow-up by means of frequent MR images of the brain to ensure control. Recurrent or new tumor deposits can be retreated by radiosurgery.

frontal lobe metastasis	several months after GK radiosurgery

 Meningiomas:

Radiosurgery is quite useful in the control of meningiomas. This can be the primary treatment for difficult to operate skull-based tumors or in the treatment of tumors recurring after open surgery. Skull- based meningiomas frequently recur after operation and conventional surgery may occasionally lead to increased cranial nerve dysfunction. Tumors arising from the cavernous sinus, and petroclival tumors of the posterior fossa are especially good candidates for GK radiosurgery, as complications of complex, skull base surgery are avoided. There is an expectation that more than 90% of tumors treated by Gamma Knife will be controlled.

Acoustic Neuromas:

Benign tumors of the vestibular nerve (vestibular schwannomas or acoustic neuromas) begin within the base of the skull and slowly expand into the skull cavity. Slow and progressive destruction of hearing in the affected ear, a sense of imbalance, weakness of facial movement, and facial numbness occurs progressively in most patients. Interestingly, there is minimal or no growth in some individuals. Thousands of patients with acoustic neuromas have been treated over the past 25 years by means of the Gamma Knife and the results compare favorably with the published results of microsurgery. Reports of reoperation on individuals treated by Gamma Knife being more difficult or dangerous are unsubstantiated. Reoperation is quite rare and failure of control may be retreated by radiosurgery. There are no reports of cancer being caused by radiosurgery.

Comparison of Radiosurgical and Microsurgical Treatment for Acoustic Neuromas

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                                               There are several factors, which influence the outcome of surgery. The most important is tumor size. Preservation of useful hearing and facial movement following open surgery is greatly limited by tumor dimensions. For example, useful hearing in the most experienced hands is unlikely in tumors over 2 cm in diameter. Other considerations include a 10 % to 20 % rate of minor complications and 2 to 4 % risk of severe complications following open surgery. This can be avoided by radiosurgery. Patients can be returned to work the day following radiosurgery!

Small acoustic neuroma before  and seven months after Gamma Knife
radiosurgery showing a slightly smaller tumor with central necrosis

There exists no published randomized trial comparing standard treatment of glioblastomas and anaplastic astrocytomas with standard treatment and radiosurgery. A recent study of patients treated with a Gamma Knife boost following surgery or biopsy, and patients treated at recurrence of disease, roughly 6 months after initial treatment showed improved survival benefit from GK radiosurgery. Survival after treatment with first recurrence of GBM was somewhat better (30 months) than initial boost treatment (20 months). About 1 in 5 patients with GBM required reoperation after GK radiosurgery, mostly for tumor recurrence rather than tumor necrosis. The 2-year survival rate for GBM was 51%. Individuals with anaplastic astrocytoma faired better with a median survival of 32 months and 2 year survival of 67%. The tumors treated with radiosurgery were small, 6 cm ³. (Kondziolka D, et al .J Neurosurg. 1997;41:776-785)

In general, we treat glioblastoma and anaplastic astrocytoma with an attempt to remove a maximal volume of abnormal tissue aimed by frameless stereotactic surgery (Sofamor-Danek Stealth system). A MR scan is performed within 48 hours of surgery and residual, enhancing tissue is boosted with radiosurgery followed by conventional radiation therapy. Alternately, recurrence is treated with GK radiosurgery as long as the tumor nidus is small. Our reoperation rate is low. Controlled studies need to be completed to conclusively demonstrate the role of radiosurgery in the treatment of malignant gliomas.

Arteriovenous malformations:

The aim of Gamma Knife treatment for AVM is total obliteration of the abnormal collection of blood vessels to reduce the chance of spontaneous hemorrhage. A widely accepted yearly risk of hemorrhage is 2 to 4%. The risk of hemorrhage may increase with age. Radiosurgery causes proliferation of the blood vessel lining, gradually occluding the AVM over time. Approximately 80% of avms under 3 cm in diameter will occlude by 2 years after treatment and perhaps 90 % three years following radiosurgery. During this time there is no increased risk of hemorrhage. Radiosurgery is sometimes the only curative treatment available in high-risk arteriovenous malformations. An example is an AVM in the brain stem, basal ganglia or eloquent brain, which bring a high risk of neurological deficit following surgery.

Trigeminal Neuralgia:

Four surgical procedures have evolved over the past 50 years to alter limbic lobe expression of emotional disorders. These new operations arose from a need to limit the untoward effects of classical frontal leukotomy: postoperative seizures, disinhibition and other personality disturbances. These techniques are anterior cingulotomy, anterior capsulotomy, subcaudate tractotomy, limbic leukotomy (combined subcaudate tractotomy, and cingulotomy. Each procedure has its advocates; each seems to produce similar results with low morbidity,

Anterior capsulotomy (AC) was introduced by Talairach in 1949 and further developed by Lars Leksell. The procedure involves the production of small, bilateral lesions in the anterior limb of the internal capsule to interrupt frontothalamic pathways as they pass beneath the head of the caudate nucleus and putamen just posterior the tip of the frontal horn of the lateral ventricle in the anterior limb of the internal capsule. Destructive lesions may be made with radiofrequency thermocoagulation or radiosurgical technique (Gamma Knife).