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What is a Gamma Knife?

A Gamma Knife is not a knife at all.
There is no incision in the scalp or opening of the skull.

Watch Our Video about the Gamma Knife

The Gamma Knife, known as the "gold standard" of brain stereotactic radiosurgery, uses precisely guided radiation to deliver unmatched outcomes exclusively for skull-based tumors and to block transmission of pain and tremors. By delivering sub-millimeter accuracy (about the width of a hair) the Gamma Knife delivers a therapeutic dose in one session, protecting healthy brain tissue that makes you the person you are.

Gamma Knife radiosurgery can be used in conjunction with whole brain radiation therapy with excellent results. It can also be used with conventional surgery as a treatment for tumors that cannot be totally removed, grow back, or, in some cases, where the tumor is inoperable.

Protecting Healthy Brain Tissue

Unlike other forms of radiation, which are aimed at a larger area or the entire brain, the Gamma Knife focuses treatment on the exact location of the tumor or abnormality, which is painstakingly mapped using computer imaging. It provides sub-millimeter precision of less than .3mm, which is about the width of a human hair. So healthy tissue is spared while a tumor-destroying dose is delivered exactly where it is needed.

The Gamma Knife is particularly effective in destroying tumors deep inside the brain that would otherwise be difficult to reach, tumors that may have been labeled as "inoperable brain tumors." It is also the best option for treating tumors near critical areas of the brain where the destruction of healthy tissue would have severe consequences.

How the Gamma Knife Works

Each of the 192 individual beams of radiation is of relatively low intensity, so the radiation has little effect on the healthy brain tissue it is moving through. However, when focused together from many different angles and concentrated, the gamma rays destroy the abnormal tissue with pinpoint accuracy. In most cases a single treatment is all that is needed, and multiple tumors or locations can be treated during a single procedure. In fact, the Gamma Knife of Spokane has treated up to 20 metatastic brain tumors at once with good results.

The use of a frame prevents movement of the treatment target and ensures continuous accuracy, unlike frameless machines such as Cyberknife and LINAC treatment, which rely on intermittent position checks for accuracy.

Gamma Knife Perfexion
range of motion

This frame-based accuracy allows delivery of a single large dose of radiation; frameless systems frequently give smaller doses in multiple fractions to allow for possible inaccuracy to average out. Gamma Knife has been used for over 800,000 treatments world-wide, more than any other stereotactic radiosurgery machine has treated. This unequalled experience has resulted in more research than for any other machine, so that methods to optimize treatment results and avoid complications are better known.

Gamma Knife treatment, also known as stereotactic radiosurgery, is not only safer, but also less costly than surgery or whole-brain radiation. It delivers a dose of radiation that can stop the growth of most tumors and even eliminate other tumors all together. Unlike whole-brain radiation, a patient can be treated multiple times with the Gamma Knife should new tumors arise over the course of treatment for systemic disease.

Traditional radiation therapy compared to Gamma Knife therapy

Traditional radiation therapy often breaks up (fractionates) delivery of radiation. This is done because cancer cells differ from healthy cells, recovering more slowly from radiation exposure and, due to differing mitotic (cell division and growth cycles) activity, are susceptible to cellular destruction. Fractions of the 'killing dose' are delivered to the target and while the healthy tissue recovers more quickly than cancer tissue, the diseased tissue then is ultimately destroyed. Fractions are often delivered with daily doses on weekdays over a period of 1 to 8 weeks, depending on the disease.

The gamma knife has 192 Co-60 sources of equal activity totalling 2.2X10 GBq. They are positioned to emanate gamma rays through a primary and a secondary collimator such that the gamma rays focus to an oblate spheroid of from 4 - 18mm average diameter. The 4mm focal ellipsoid has a penumbre of 1mm from the 50%-10% of its maximum profile. With careful positioning and weighting of the 4,8,14, and 18mm focal spheroids, extremely sharp dose volume histograms can be attained for the target and nearby critical structures. Blocking of up to half of the 201 sources affords even tighter control of dose shaping to the target and adjacent critical structures.

Single Strand Break and Double Strand Break -- Courtesy of NASA
Single Strand Break and Double
Strand Break -- Courtesy of NASA

One-day Procedure

It is a one-day procedure that requires little or no anesthesia. You or your loved one will be treated in the morning, and in most cases (approximately 98% of patients) can go home that afternoon. The patient usually returns to normal activities the next day or within days of treatment.


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