Gamma Knife

Gamma Knife Radiosurgery

 

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 effective dose of radiation is given in a single session and avoids potentially harmful radiation to surrounding brain structures. Professor Lars Leksell, a Swedish neurosurgeon, developed stereotactic devices (used to guide the gamma rays) and devised the concept of radiosurgery in the early 1950s. 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 140,000 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. Professor Leksell’s concept of radiosurgery has proven to be a true advance in the treatment of intracranial disease.

Stereotactic techniques can also be used to accurately aim fractionated doses of gamma rays or x-rays to a target; administering the treatment in small doses over a few days. This technique is a compromise between radiosurgery and conventional radiotherapy and is termed stereotactic radiotherapy.

What abnormalities can the Gamma Knife treat?


Here is a partial list of some of the disorders amenable to radiosurgery:

Brain Tumors:
Glioblastoma
Anaplastic astrocytoma
Gliomas / Astrocytoma
Oligodendroglioma
Ependymoma
Pilocytic astrocytoma
Meningioma
Pituitary tumors
Pineal region tumors
Acoustic Neuroma
Neuromas of the cranial nerves
Glomus jugulare tumor
Metastatic brain tumors

Vascular Abnormalities:
Arteriovenous malformations
Cavermous malformations
Skull Base Tumors:
Invasive squamous and basal cell carcinoma
Chordoma
Chondrosarcoma
Esthesioneuroblastoma

Functional Problems:
Trigeminal neuralgia
Parkinson's disease
Essential tremor
Obsessive Compulsive Disorder

Ocular Tumors:

Uveal melanoma
Orbital metastases
Optic nerve sheath meningioma

How is Gamma Knife Radiosurgery performed?

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:

Gamma Knife Radiosurgery frame placementEarly 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. The frame remains in place until the end of treatment later in the day. 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:

Gamma Knife Treatment PlanningThe greatest advances since the first Gamma Knife treatment in 1968 have been the advent of CT and MR imaging as well as high speed data processing which allows surgeons to treat intracranial disease with computer techniques. The CT/MR images are displayed by software designed for conformal treatment planning. This allows the Gamma Knife’s highly focused energy to accumulate within the target volume while minimizing radiation to sensitive adjacent brain tissue. The neurosurgeon, radiation oncologist, and physicist develop the conformal treatment plan.

The Gamma Knife:

gamma knife 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 action 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 cannot focus gamma rays; rather individual beams are allowed to summate by overlapping at the focal point of the collimator which achieves the same effect. A second collimator, which fits within the primary collimator, allows the beam focus size to be adjusted from 4mm to 18mm 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. 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.

 

To contact the San Diego Gamma Knife Center please follow this link - www.sdgkc.com