Gamma Knife: Stereotactic Radiosurgery

A modern definition of stereotactic radiosurgery (SRS) has been approved in the USA by the AANS Board of Directors, Executive Committee of the Congress of Neurological Surgeons and the Board of Directors of the American Society of Therapeutic Radiology and Oncology.

• Stereotactic radiosurgery is a distinct discipline that utilizes externally generated ionizing radiation in certain cases to inactivate or eradicate defined target(s) in the head and spine without the need to make an incision. The target is defined by high-resolution stereotactic imaging. To assure quality of patient care the procedure involves a multidisciplinary team consisting of a neurosurgeon, radiation oncologist and a medical physicist.
• Stereotactic radiosurgery typically is performed in a single session, using a rigidly attached stereotactic guiding device, other immobilization technology and/or a stereotactic guiding device, other immobilization technology and/or a stereotactic image-guidance system. SRS can be performed in a limited number of sessions, up to a maximum of five.
• Technologies that are used to perform SRS include linear accelerators, particle beam accelerators and multisource Cobalt 60 units. In order to enhance precision, various devices may incorporate robotics and real time imaging.

Unlike conventional surgery, SRS for the most part is an outpatient procedure, involves no incision, rarely requires a general anesthetic, can be done while on blood thinners (i.e. Plavix, Coumadin), does not result in hair loss and does not disrupt ongoing concurrent treatments such as chemotherapy. Whole brain radiation in which a patient receives a small dose of radiation each day over weeks can be given only once. SRS can be repeated.

Dr. Shedden has well over 15 years experience with the Leksell Gamma Knife® using various models including the most recent Perfexion™ which was recently installed at St. Luke’s The Woodlands Hospital.

SRS using the Perfexion™ Gamma Knife can be used for many different intracranial disorders including but not limited to arteriovenous malformations (AVMs), arteriovenous fistulas (AVFs), several different kinds of benign and malignant brain tumors, trigeminal neuralgia (facial pain syndrome) and several other disorders (see below).

Conditions that can be treated using Gamma Knife:

• Arteriovenous Malformations (AVMs) are an abnormal tangle of poorly developed blood vessels (arteries & veins) that have a higher propensity to bleed than normal vessels. They are thought to be congenital and in addition to bleeding into the brain they can also cause seizures. Management of an AVM is based on the patient’s age, their location in the brain (lobe, side, deep or superficial), their size and their feeding vessels and drainage pattern (i.e. deep/superficial veins).

AVMs are for the most part manged by a multidisciplinary team including a neurosurgeon, neuro interventionalist and a radiation oncologist. Options include observation, surgery, emboliztion of the AVM and stereotactic radiosurgery using Gamma Knife. The risk of rupture is approximately 3.5% per year and the size of the AVM depends upon how quickly the Gamma Knife will eradicate the AVM. Some AVMs are very large (> 3.5cm) and the Gamma Knife with or without embolization may have to be staged. 

For a more in-depth understanding of the above topic please refer to the following article:

Back, A.G., Vollmer, D.G., Zeck, O., Shkedy, C., Shedden, P.M.: Staged Gamma Knife Radiosurgery for the treatment of large arteriovenous malformations. Leskell Gamma Knife Society 14^th International Meeting. Quebec, Canada, May 2008

• Brain Tumors can be divided into two categories:  primary and secondary. Primary tumors arise from the brain tissue itself while secondary tumors come from other sources such as lung, breast, colon, etc.

Gamma Knife has been used un almost all brain tumors at some point but clearly has an important role in the management of meningiomas, acoustic neuromas, pituitary tumors, hemangioblastmas, craniopharyngiomas, pineal region tumors and metastatic brain tumors such as melanoma, breast, colon, lung, etc. The size obviously plays a role and < 3-5cm is better. The number of metastatic lesions is also an important factor in Gamma Knife treatment. There appears to be a role for Gamma Knife as the primary treatment of metastatic lesions allowing the patient to avoid whole brain radiation.

The benefits of Gamma Knife treatment are many but include outpatient (no ICU stay) single treatment day and a follow up regime that overall should decrease your frequency of imaging (i.e. fewer MRIs results in lower costs).

• Trigeminal Neuralgia (tic douloureux) is an extremely painful syndrome of the face that affects either the VI, VII OR VIII branches of the trigeminal nerve. Often patients are treated with Tegretol and respond well. Some patients do not tolerate Tegretol or other medications and seek other forms of treatment. These can include but are not limited to glycerol injections, radiofrequency ablation and microvascular decompression (MVD). There are pros and cons to all modalities and often the risks outweigh the benefits especially in the older age groups where concurrent medical problems exist.

Gamma Knife has been used successfully in patients with classic TGN. High dose radiation is given by the Gamma Knife to the trigeminal nerve. If there is a relapse years later it can be repeated.

Other Cases:

Gamma Knife has been in use in the USA since the mid 80’s and its role has increased as medicine and technology have advanced. SRS using Gamma Knife can be used for tremors, some forms of epilepsy and experimentally in obsessive compulsive disorder (OCD). However, the future will be our ability to identify the “areas” of the brain that can be lesioned by Gamma Knife with accuracy and give the desired affect (i.e. “over-eating center” for obesity). Treatment of functional issues with Gamma Knife is sure to increase over time.