The Gamma Knife does not actually involve cutting a tumor with a knife or scalpel. Rather the gamma knife procedure, also known as stereotactic radiosurgery, uses high-energy gamma rays to pinpoint and destroy tumors or other brain abnormalities.

With the help of computerized imaging, our neurosurgical team is able to map the exact location of the lesion, and then direct the beams at the tumor with extreme accuracy. After targeting the affected area, the beams are used to deliver enough radiation to kill or contain the affected brain tissue, while sparing nearby healthy tissue and other parts of the brain.

The Gamma Knife uses 201 emitting sources to deliver a high dose of a substance called Cobalt-60. The beams emitting from these Cobalt-60 sources are delivered through a device known as the collimator helmet, which is fitted to the patient's head.   Although each individual beam is relatively weak and does not damage tissue, when focused together, the combined beams can help destroy the tumor.

The Gamma Knife is particularly effective in reaching small, localized tumors deep inside the brain that would otherwise be difficult to reach. It is usually used for tumors no more than about an inch in diameter.

Gamma Knife radiosurgery is most commonly used for:

• Brain tumors. Gamma knife therapy can treat tumors in hard to reach areas of the brain. 
• Arteriovenous malformations (AVMs). AVMs are an unusual collection of blood vessels in which arteries and veins connect directly, instead of through the normal network of capillaries. When AVMs occur in the brain, they can cause severe bleeding, headaches or seizures. In these cases, Gamma knife therapy may be a better option than traditional surgery. 
• Trigeminal neuralgia. This nerve disorder causes disabling facial pain that feels like an electric shock. Gamma knife surgery can create a lesion on the nerve, blocking its pain signals. Radiosurgery for trigeminal neuralgia is typically performed for older patients or for patients with recurrent pain after other operations. 
• Acoustic neuromas. Also known as schwannomas, acoustic neuromas are benign (noncancerous) tumors that affect balance and hearing. Gamma knife therapy can help limit these tumors, reducing the risk of deafness or paralysis of the face. 
• Pituitary tumors. The pituitary gland that is located at the base of the brain and controls hormone functions throughout the body. Gamma knife therapy can help reduce the abnormal hormone activity that may result from a pituitary tumor.

Gamma knife surgery is offered at the UW Gamma Knife Center at Harborview Medical Center, Seattle, Washington.

Because Gamma Knife surgery requires precise positioning, special equipment is needed. A specialized helmet and frame are fitted to the patient’s head and serves two functions:

1. Helps aim the Gamma Knife at the right location in the brain 
2. Keeps the head steady and properly positioned during the procedure

Image Mapping and Planning

Once the target area is located, imaging software is used to create three-dimensional models of the brain. These models closely match the shape of the tumor or the affected area. Then a prescription dose is determined. This dose will be dependent upon the type of lesion, location, size and any prior therapy. Planning generally takes about 30 minutes.

Treatment

The doctor may advise you not to eat or drink anything after midnight the night before the Gamma Knife therapy. It is also advisable not to wear jewelry or other extra items the day of the procedure.

Treatment is completed in a single session. Depending upon the treatment plan and how many radiation shots the patient requires (usually 1-4), the procedure is generally completed in less than an hour.

During treatment, the patient is monitored by means of a video system and a two-way intercom that allows the patient to talk with the physician during the procedure. When the procedure is completed, the head frame is removed and the patient is evaluated and prepared for discharge. Many patients return to their normal activities the following day.

It may take many weeks or even up to several years before the effects of Gamma Knife treatment become apparent. The patient’s progress is monitored through follow-up imaging studies.

Some patients experience persistent swelling after the treatment. Steroid medications may be prescribed to help treat this type of swelling.

More than 100,000 patients have been treated worldwide with a variety of different types of tumors and AVMs. Patients with the following diseases may also be candidates for the Gamma Knife procedure:

• Epilepsy
• Chronic pain
• Parkinson's disease 
• Patients who have had a recurrent brain tumor following surgery

A multidisciplinary team of neurosurgeons and oncologists will determine if Gamma Knife is the best option for each particular patient.

Treating Children

Some brain lesions in pediatric patients are suitable for the Gamma Knife. For our young patients, general anesthesia is used and the hospital stay is generally overnight in our pediatric care unit. Harborview Medical Center treats nearly 500 children a year and has a close relationship with Children's Regional Hospital and Medical Center. We have a pediatric intensivist and pediatric nurse educator on staff as well as recreational therapists to make your child's stay as comfortable as possible.

Consultation and Referrals
Typically, patients are seen in consultation and initially by a neurosurgeon or a radiotherapist. Then, our radiosurgery panel evaluates each case. After further evaluation, the appropriate method of therapy is tailored for each individual. In some cases, patients will require MRI, CT and functional MRI, angiograph and neurophysiological evaluation.

The Gamma Knife is used most effectively in the treatment of intracranial tumors up to an inch in size, such as: 

• Acoustic tumors 
• Meningiomas – noncancerous (benign) brain tumor in the cells of the outer covering of the brain (meninges). 
• Craniopharyngiomas – benign tumors that occur most commonly in childhood and adolescence or later adult life after age 50 
• Arteriovenous malformations (AVMs)

It is also used in the treatment of lesions that cannot be reached by conventional surgery, and is used along with radiation therapy and in the treatment of recurrent tumors.

The Gamma Knife may also be used to help stop the growth of brain metastases from cancer. Studies also indicate that pituitary tumors, tumors that form in a gland located deep inside the brain, can be treated using this treatment.

The patient’s recovery depends on the size and type of abnormality, ranging from a few weeks to several years. Most abnormalities disappear gradually and others just stop growing. However, in some cases the tumor or AVM might not respond to Gamma Knife therapy.

Some side effects you may experience after Gamma Knife treatment includes: 

• Nausea 
• Headaches 
• Skin irritation 
• Superficial lesions 
• Patchy hair loss 
• Neck stiffness 
• Dry mouth 
• Pain at the frame securing sites

Some patients experience a temporary swelling in the area near the treatment site. If the swelling persists, your doctor may recommend steroid medications.

The decision to use Gamma Knife radiosurgery should be made after careful consideration with your doctor. The procedure may be used to treat brain tumors or other brain abnormalities, or it may be used to help control the spread of cancerous cells in the brain.