Gamma Knife Explained

Gamma Knife® radiosurgery is done only for tumors and other medical problems of the head. For tumors and problems elsewhere in the body, other radiosurgery systems may be used. Gamma Knife® surgery represents a major advance in brain surgery, and in the last three decades has changed the landscape within the field of neurosurgery. Its development has enhanced neurosurgical treatments offered to patients with brain tumors and vascular malformations by providing a safe, accurate and reliable treatment option. Gamma Knife® enables patients to undergo a non-invasive form of brain surgery without surgical risks, a long hospital stay or subsequent rehabilitation.

The clinical effectiveness of Gamma Knife® has been documented over four decades. More than 700,000 cases have been treated worldwide, providing data for over 4,000 publications in peer-reviewed medical literature.

Gamma Knife® surgery is unique in that no surgical incision is made to expose the inside of the brain, thereby reducing the risk of surgical complications and eliminating the side effects and dangers of general anesthesia. The “blades” of the Gamma Knife® are the beams of gamma radiation programmed to target the lesion at the point where they intersect. In a single treatment session, 192 beams of gamma radiation focus precisely on the lesion. Over time, most lesions slowly decrease in size and dissolve. The exposure is brief and only the tissue being treated receives a significant radiation dose, while the surrounding tissue remains unharmed.

With the Gamma Knife®, a surgical incision is not required; the attendant risks of open neurosurgical procedures (hemorrhage, infection, cerebrospinal fluid leakage, etc.) are therefore avoided.

Conditions for which the Gamma Knife® is considered most effective are:

  1. Intracranial tumors such as acoustic neuromas, pituitary adenomas, pinealomas, craniopharyngiomas, meningiomas, chordomas, chondrosarcomas, metastases and glial tumors.
  2. Vascular malformations including arteriovenous malformations.
  3. Functional disorders such as trigeminal neuralgia and obsessive-compulsive disorder.

The Gamma Knife® technology can be used to treat those who do not require immediate surgical relief of disabling symptoms and those whose tumors are, in general, 3 cm or less.

As an example, Meningiomas are the most common benign brain tumors. Gamma Knife® has a 95% control rate for the treatment of meningiomas. The following images show the decrease in meningioma after Gamma Knife® treatment.

Leksell Gamma Knife® is a registered trademark of Elekta Instruments, Inc.

A patient's perspective

What is involved in a typical Gamma Knife® Treatment?

On the day of treatment, the patient is given light sedation. Next, local anesthesia is used to secure an head frame to the patient’s head. The frame is used in conjunction with an imaging procedure to accurately locate the target. With the frame in place, the patient undergoes an MRI or CT scan, or in the case of an arteriovenous malformation (AVM), angiography, in order to locate the lesion in the brain to be treated. Using the imaging procedure, the treating team can define the position of the lesion(s) inside the patient’s head. While the patient rests, the treatment team (which typically consists of a neurosurgeon, radiation oncologist and physicist) uses a computer to devise a treatment plan. This takes from 30 to 90 minutes to complete, depending upon the geometry and location of the target(s). When the individual treatment plan is completed, the patient lies on the Gamma Knife couch so that their head is precisely positioned for treatment. The patient is then moved automatically, into the machine, and treatment begins. Treatment typically lasts from 20 minutes to 2 hours, during which time the patient feels nothing. At the completion of the treatment, the patient is automatically moved out of the machine, and the head frame is removed. The patient usually goes home at this point, but may remain in the hospital overnight for observation on occasion.

How many patients have received Gamma Knife® treatment?

Gamma Knife® used in over 70,000 patients every year.

What Are The Possible Side Effects Of Gamma Knife® Radiosurgery?

Gamma Knife® radiosurgery doesn’t involve surgical incisions, so it’s generally less risky than open craniotomy where the possibility exists for problems with anesthesia, bleeding and infection.

Early side effects following Gamma Knife® radiosurgery are usually temporary.  They may include:

Fatigue – Fatigue and tiredness may occur for the first few weeks after Gamma Knife® radiosurgery.  This is very common after any radiosurgery treatment.

Swelling – Swelling in the brain at or near the treatment site can cause symptoms such as headache, nausea or vomiting.  Your doctor may prescribe corticosteroid medications to prevent such effects from occurring or may wait to treat symptoms if they should appear.

Scalp and hair concerns – Redness, irritation or sensitivity may occur at sites where the frame is attached to your head.  Rarely, patients may experience some temporary hair loss.

Other side effects may occur dependent upon the target site and the dose of radiation received.  This should be discussed thoroughly with your treating physician.

What studies have been done or are being done to show its effectiveness?

The number of peer-reviewed, published scientific articles documenting patient outcomes with Gamma Knife® far outweighs any other form of stereotactic radiosurgery. Gamma Knife® centers and universities have published more than 4,000 papers and have treated more than 850,000 patients worldwide during the last 40 years. The fact that 75% of all published radiosurgical literature including most of the multicenter trials is based on the use of the Gamma Knife® is especially significant given that both Gamma Knife® and Linac systems were introduced in the same era.

View Studies

Gamma Knife versus Linac Radiosurgery

Novalis Tx®, CyberKnife®, TomoTherapy®

Linac is short for the term linear accelerator. Linear accelerator machines produce radiation that is referred to as high energy X-ray. A linear accelerator machine is designed to be a general purpose radiation delivery machine (not brain specific like the Gamma Knife®)  and in general requires modifications to enable it to be used for radiosurgery.

Radiosurgery can be performed with linear accelerator machines but requires 2-5 treatments versus 1 treatment with Gamma Knife®. The tumor receives a very high one time dose of radiation with radiosurgery, and smaller doses over time with radiation therapy. This can result in more side effects, some of which may be permanent. More importantly, a reduced amount of radiation delivered to the tumor with each radiation therapy treatment, rather than a very high one time dose using the Gamma Knife®, can result in less tumor control and poorer outcomes than with radiosurgery.

Because of the significant risks associated with millimeter errors in targeting for the brain, Gamma Knife® surgery combines physical immobilization of the patient’s head with ultra-accurate targeting and delivery. The most important measurement of accuracy is the total clinical accuracy. This is an end-to-end measurement combining mechanical and radiological accuracy plus imaging. Gamma Knife®’s average achievable clinical accuracy is 0.48mm compared to CyberKnife®’s linac machine average total of 2.10mm. The precision of brain stereotactic Gamma Knife® radiosurgery results in minimal damage to healthy tissues surrounding the target.