Gamma Knife radiosurgery


Stereotactic radiosurgery (SRS) treats brain disorders with a precise delivery of a single, high dose of radiation in a one-day session. Focused radiation beams are delivered to a specific area of the brain to treat abnormalities, tumors or functional disorders. The surgery is not invasive nor uses any sort of surgical tools other than the gamma radiation. During the procedure, 192 single gamma beams protrude through the skull and meet at one highly focused point inside of the brain to treat abnormalities, tumors, or other functional disorders. What was once called an impossible task in eliminating deep brain abnormalities and tumors is now available with gamma radiation. These small beams do not cause enough damage to living, healthy tissue, but become extremely potent once they are combined on point to deliver a high amount of radiation therapy. While this technique is typically used upon patients with severe health issues within the brain, there are a few Centers of Excellence that can treat the body in the same fashion with gamma radiosurgery using special technology.


Fractionated stereotactic radiation treatments-which are received over a period of days or weeks-may be administered to the body with the assistance of removable masks and frames that achieve a lesser degree of immobilization.

Prior to Surgery

Patients must have a lightweight stereotactic frame placed over the head that is attached by screws. This frame must stay on your head until after the surgery. This must happen so that the patient's head stays in a stable position during imaging and treatment. This takes roughly 15 minutes to attach. Afterwards, a special device is placed upon the frame and and used to find the position of your head in relation to the frame.Once this is taken care of, the patient goes through imaging such as MRI, A coordinate box is used during imaging to provide reference points on the images for the treatment plan. These treatments must be repeated with the frame on the patients head to define the exact location, size, and shape of the treatment area. These images are sent to a computer to help with developing a treatment plan to find the precise area that needs to be affected during the surgery.
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How it Works:
Stereotactic radiosurgery works the same as all other forms of radiation treatment. It does not remove the tumor or lesion, but it distorts the DNA of the tumor cells. The cells then lose their ability to reproduce and retain fluids. The tumor reduction occurs at the rate of normal growth for the specific tumor cell. In lesions such as AVMs (a tangle of blood vessels in the brain), radiosurgery causes the blood vessels to thicken and close off. The shrinking of a tumor or closing off of a vessel occurs over a period of time. For benign tumors and vessels, this will usually be 18 months to two years. For malignant or metastatic tumors, results may be seen in a few months, because these cells are very fast-growing.

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The Gamma Knife Unit

The Gamma Knife contains 192- 201 cobalt-60 sources of approximately 30 curies each, placed in a circular array in a heavily shielded unit. The unit directs gamma radiation very precisely to a target point. Such target points selected in the brain can be placed at the center of the radiation focus, allowing an effetive radiation dosage to be delivered in one treatment session. The Gamma Knife has proved effective for thousands of patients with benign or malignant brain tumors, vascular malformations, pain or other functional problems.

Positives to Gamma Knife Radiosurgery:
  • Painless procedure
  • Relatively quick (10-70 minutes), leave the same day
  • Not invasive, no scarring, no open-skull surgery, bloodless
  • Possible to get to deeper abnormalities or tumors
  • Extremely precise
  • Radiation falloff is steep, so single beams leave no damage to healthy tissue
  • Adults do not require general anesthesia
  • Live monitoring of the patient with two-way voice contact between patient and physician
  • Seventy to 90 percent of AVMs are completely obliterated within three years
  • No other surgical procedure has achieved such favorable outcome with so little morbidity.
  • Does not result in hair loss

Downsides to Gamma Knife Radiosurgery:
  • Possible edema or swelling
  • Symptoms created by possible swelling
  • Necosis - Necrotic tissue caused by the procedure can harm the surrounding area, but rarely
  • Delayed radiation symptoms(Below)
  • Decreased Intellect
  • Memory impairment
  • Confusion
  • Personality changes

What conditions can be treated by the Gamma Knife?

  • Malignant tumors such as metastases
  • Benign tumors such as meningiomas, acoustic neuromas, pituitary tumors and low grade glioma and skull-based tumors
  • Vascular malformations such as arteriovenous malformations (AVMs) and cavernous angiomas
  • Functional disorders such as trigeminal neuralgia


UPMC physicians have performed Gamma Knife radiosurgery on more than 1,600 patients with acoustic neuroma, a deafness-causing tumor of the sheath of the hearing nerve. Gamma Knife surgery prevented tumor growth in 97 percent of patients, and up to 80 percent of patients retained their hearing on a long-term basis. Recent UPMC studies suggest that Gamma Knife radiosurgery can lengthen life for patients with certain malignant brain tumors as well.

Web Resources:

Gamma Knife
Gamma Knife Frequently Asked Questions
Mayo Clinic

Related Terminology:

Gamma Ray:
  • Electromagnetic radiation emitted by radioactive decay and having energies in a range from ten thousand (104) to ten million (107) electron volts.
  • The use of ionizing radiation, either from an external source such as an x-ray machine or from an implant, to destroy cancerous or other diseased tissue.
Stereotactic surgery:
  • Minimally invasive form of surgical intervention which makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action.
  • An abnormal growth of tissue resulting from uncontrolled, progressive multiplication of cells and serving no physiological function; a neoplasm.
  • Emission and propagation of energy in the form of rays or waves.

Citations/References: (Penn Medicine) (Penn Medicine)