NEUROSURGERY ARTICLES

GAMMA KNIFE STEREOTACTIC RADIOSURGERY

by Franklin Westhout, M.D. and Mark Linskey, M.D.

Stereotactic radiosurgery (SR) is a neurosurgical procedure that delivers a single very large dose of radiation to a precisely defined and targeted volume of tissue with little dose delivered to tissue as close as 2 mm away. The goal of the procedure is to permanently damage or biologically inactivate all the tissue within the target volume, which can be a tumor (malignant or benign), an arteriovenous malformation (AVM), or a normal tissue structure requiring a therapeutic lesion (e.g. trigeminal neuralgia-TN). While many technologies can be utilized to deliver SR (X-Knife®, Novalis®, Varian Trilogy®, Cyberknife®, etc.), none has been able to exceed the safety and accuracy of the Gamma Knife® (GK). Certainly, no other technology even approaches the long-term clinical experience and proven long-term and published clinical results of GK stereotactic radiosurgery.

How the Gamma Knife Works

Stereotactic radiosurgery is only possible because the neurosurgeons are able to: 1) concentrate and focus the radiation tightly, and 2) targeting is so accurate that not only are they sure they are treating the whole lesion but, just as importantly, they are sure that they are excluding the important surrounding normal structures from receiving this high radiation dose. The focusing and concentration is achieved by the Gamma Unit, which is a machine where 201 radiation sources are arranged in an array around the head to send very fine beams of radiation through the patient to a single intersection focus spot. Each beam emits a very small dose of radiation, but at the point of intersection, the dose is 201 times stronger. Precise targeting is done with a neurosurgical procedure called stereotaxis. A targeting frame is positioned over the patients head and attached in four places around the head using fine pins and local anesthetic. An MR image and sometimes an angiogram are then obtained with the frame in place. Every point inside the patient's head can now be defined by a coordinate on the attached frame with an accuracy of 0.2 - 0.5 mm in three dimensions. A treatment plan is then devised so that the entire tumor, or AVM, can be treated. GK works equally well for benign tumors and malignant tumors and equally well for malignant tumors traditionally thought to be radioresistant.

Clinical Uses of Gamma Knife Stereotactic Radiosurgery

Radiosurgery has a well-established role for treating selected patients with small AVMs. It has emerged as a preferred treatment for TN, when potential curative surgery has failed, or is either not medically advisable or wanted. For tumors, SR has already assumed the dominant clinical role for the surgical treatment of selected patients with multiple metastatic brain tumors of appropriate size, and remains an attractive alternative to microsurgery for selected patients with single metastatic brain tumors. It is emerging as a preferred initial treatment for many benign tumors of appropriate size, particularly those located in skull base locations.

UCI Gamma Knife Stereotactic Radiosurgery

UCI SR is performed at the Hoag/UCI Gamma Knife Center in Newport Beach. UCI patients are treated by a multidisciplinary team of UCI radiation-oncologists and neurosurgeons led by Dr. Mark Linskey. Dr. Linskey has been performing GK SR since 1987. He was trained on the first Gamma Unit in the U.S. at the University of Pittsburgh, and is one of the academic pioneers of the technique. He is one of 12 physicians world-wide serving on the international scientific advisory board for the company that developed and continues to refine the GK. The Hoag/UCI unit represents his fourth gamma knife center and he has extensive experience and publications in this area. The Hoag/UCI Gamma Knife Center is directed by Dr. Christopher Duma who has been performing GK SR since 1991, and has been at the Hoag/UCI Gamma Unit since 1997. He treats patients from his community practice on the unit. He also trained on the University of Pittsburgh Gamma Unit and has extensive experience and publications in this area. Dr. Duma is a member of the voluntary UCI Neurosurgery faculty.

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