(Stereotactic radiosurgery, Gamma Knife surgery)
What is Gamma Knife radiosurgery?
Gamma Knife radiosurgery, also called stereotactic radiosurgery, is a very precise form of therapeutic radiology. Even though it is called surgery, a Gamma Knife procedure does not involve actual surgery, nor is the Gamma Knife really a knife at all. It uses beams of highly focused gamma rays to treat small- to medium-sized lesions, usually in the brain. Many beams of gamma radiation join to focus on the lesion under treatment, providing a very intense dose of radiation without a surgical incision or opening.
Gamma Knife radiosurgery is called "surgery" because the end result is very similar to physically removing the lesion with surgery. The beams of radiation are very precisely focused to reach the tumor, lesion, or other area being treated with minimal effect on surrounding healthy tissue.
Gamma Knife radiosurgery is most often used to treat small and medium tumors and other lesions in the brain. It is also used to treat certain neurological conditions, such as trigeminal neuralgia (a condition in which pressure on the trigeminal nerve causes spasms of extreme facial pain) and acoustic neuroma (a noncancerous tumor in the brain that affects the nerves that control hearing).
Gamma Knife radiosurgery may be used in situations where the brain lesion cannot be reached by conventional surgical techniques. It may also be used in persons whose condition is such that they might not be able to tolerate a surgical procedure, such as craniotomy, to treat their condition.
Because the therapeutic effects of a Gamma Knife procedure occur rather slowly over time, it is not used for persons whose condition requires more immediate therapy.
How does Gamma Knife radiosurgery work?
Radiosurgery works in the same manner as other types of therapeutic radiology: it distorts or destroys the DNA of tumor cells, causing them to be unable to reproduce and grow. The tumor will shrink in size over time. For blood vessel lesions such as an arteriovenous malformation (AVM), the blood vessels eventually close off after treatment.
Gamma Knife treatment generally involves these steps:
Head frame placement. In order to keep the head from moving during treatment, a box-shaped frame is attached to the head. Pins designed specifically for this purpose fasten the head frame to the skull. The head frame also is a guide to focus the gamma ray beams to the exact location of the lesion being treated.
Tumor or lesion location imaging. Once the head frame is in place, the exact location of the lesion to be treated will be determined using computed tomography (CT scan) or magnetic resonance imaging (MRI).
Radiation dose planning. After the CT or MRI scan has been completed, the radiation therapy team will determine the treatment plan. The results of the imaging scan, along with other information, will be used by a medical physicist to determine the best treatment.
Radiation treatment. After being positioned for the treatment, a type of helmet with many hundreds of holes in it is placed over the head frame. These holes help to focus the radiation beams on the target. Treatment will last a few minutes up to a few hours, depending on the type and location of the area being treated. Generally, only one treatment session is required for a lesion.
A Gamma Knife procedure involves a treatment team approach. The treatment team generally includes a radiation oncologist (a physician specializing in radiation treatment for cancer), a neurosurgeon and/or a neuroradiologist, a radiation therapist, and a registered nurse. In addition, a medical physicist and a dosimetrist work together to calculate the precise number of exposures and beam placement necessary to obtain the radiation dose that is prescribed by the radiation oncologist. Your treatment team may include other healthcare professionals in addition to or in place of those listed here.
The Gamma Knife system is one of three types of radiosurgery systems. Gamma Knife systems are cobalt 60 systems, which means they use cobalt as a source for gamma rays. During Gamma Knife treatment, the equipment remains stationary (does not move).