Gamma Knife radiosurgery is a highly specialized technique used to treat tumors and lesions of the brain and surrounding structures with radiation. As used by the physicians of the Ear Institute of Chicago, the Gamma Knife is used to treat certain tumors in and around the ear (specifically, acoustic neuromas, meningiomas and certain glomus tympanicum tumors). Despite its name, Gamma Knife radiosurgery does not require an incision; the skull is never opened. The “blades” of the Gamma Knife are the beams of gamma radiation computer programmed to target the lesion at the point where the beams intersect. In a single treatment session, 201 beams of gamma radiation focus precisely on the lesion. Each individual radiation beam is too weak to harm the brain tissue it passes through. The damage occurs only at the spot where all the beams overlap. With the help of a computer, this spot can be accurately plotted to within a fraction of a millimeter.

Gamma rays entering target (side view)

Gamma Knife Radiosurgery is not designed to remove an acoustic neuroma or glomus jugulare tumor. Instead, Gamma Knife Radiosurgery is used to control the growth of these tumors. Specifically, the Gamma Knife is designed to prevent tumor growth. A small percentage of tumors treated with Gamma Knife Radiosurgery will continue to grow and may require traditional, open surgical treatment.

There are several benefits of Gamma Knife radiosurgery. Patient Benefits:
• Noninvasive, no incisions
• No hospitalization required
• Painless
• A single, outpatient treatment session
• Little to no recovery time
• Allows for an immediate return to daily activities
• Minimal, if any, side effects due to pinpoint precision of high-dose radiation delivery
• Minimal radiation exposure to healthy tissue surrounding a tumor

The Ear Institute of Chicago performs Gamma Knife Radiosurgery at the Illinois Gamma Knife Center located at Alexian Brothers Medical Center in Elk Grove, Illinois. The Illinois Gamma Knife Center uses the Leksell® Perfexion™, which is considered by many to be the gold standard in stereotactic radiosurgical treatment for lesions in the skull.

History of the Gamma Knife

In the early 1950’s Professor Lars Leksell, a Swedish neurosurgeon, first developed the concept of radiosurgery along with stereotactic devices (used to guide the gamma rays). Professor Leksell worked with a physicist, Borje Larsson, to build 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. Worldwide, the Leksell ® Gamma Knife has been used to treat more than 330,000 malignant and benign tumors and tens of thousands of other brain conditions. Since the development of the Gamma Knife, over 2,500 peer-reviewed medical research articles support the use of Gamma Knife.
(Leksell Gamma Knife is a registered trademark of Elekta Instruments, Inc.)

Head frame with CT/MRI box attached to the frame

1. Frame placement. A lightweight frame is fitted over the patient’s head and attached with screws using local anesthesia. The frame serves two purposes: On the side of the frame are markers that allow the treatment team to pinpoint areas that will receive treatment. The frame also keeps the patient’s head immobile during the radiation procedure.

3-D image of an acoustic neuroma (in yellow) (top view)

2. Imaging Study. Imaging studies are obtained using MRI, CT scan, angiography, or a combination of these technologies. The imaging studies produce a three-dimensional map of the tumor and the surrounding brain structures.

Screenshot of computer workstation view of left-sided 1.8-cm acoustic neuroma prior to planning. (Clockwise from top left: axial, coronal, axial, sagittal views)

Left-side 1.8-cm acoustic neuroma prior to treatment plan. (Yellow=outline of radiation target around tumor)

Left-side 1.8-cm acoustic neuroma treatment plan. (Yellow=outline of radiation target around tumor and red circles=radiation “shots”)

3. Treatment planning. Based on the imaging studies, your physician works with a radiation oncologist and a medical physicist to develop the treatment plan that accurately targets the tumor with exact precision, sparing surrounding tissue as much as possible (i.e. a plan than conforms closely to the shape of the lesion).

Perfexion Gamma Knife radiation bed and machine

4. Radiation treatment. Treatment begins by first having the patient lie on the Gamma Knife bed (Left Figure Below). The head frame is fitted into a helmet with 201 holes in the helmet (Right Figure Below). The helmet helps to guide 201 sources of cobalt 60 based (photon) radiation beams to accurately target the tumor. After the helmet is placed, the bed is precisely moved into the domed unit and treatment begins. Depending on the size and location of the tumor, the actual time of radiation delivery could range from a few minutes to over an hour.

5. Removal of the head frame. Removal of the frame is a painless procedure. Most patients are able to go home shortly after the head frame is removed.

For Frequently Asked Questions regarding Gamma Knife Radiosurgery, click here.