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Stereotactic radiosurgery - Gamma Knife

Stereotactic radiosurgery (SRS) is a form of radiation therapy that focuses high-power energy on a small area of the body.

Despite its name, radiosurgery is not actually a surgical procedure -- there is no cutting or sewing, rather it is a radiation therapy treatment technique.

More than one system is used to perform radiosurgery. This article is about Gamma Knife radiosurgery.


The Gamma Knife radiosurgery system is used to treat either cancers or growths in the head or upper spine area. For cancers or growths lower down in the spine or anywhere else in the body, another focused radiosurgery system may be used.

Before treatment, you may be fitted with a "head frame." This is a metal circle that is used to precisely position you into the machine to improve accuracy and pinpoint targeting. The frame is attached to your scalp and skull. The process is performed by a neurosurgeon, but does not require cutting or sewing. Some Gamma Knife procedures do not need a head frame; they use a face mask or net, and they are called "frameless." When a frame is used, here is what you should know:

  • The head frame is placed over your head, and four small pins are attached to your skull. The pins are designed to hold the head frame in place by going through the skin into the surface of your skull.
  • You are given a local anesthetic and should not feel pain, but rather only pressure. You also are usually given medicine to help relax you during the fitting procedure.
  • The frame will remain attached for the whole treatment procedure, usually a few hours, and then will be removed.

Whether or not a frame is attached to your head, imaging tests such as CT, MRI, or angiogram are done. The images show the exact location, size, and shape of your tumor or problem area and allow precision targeting.

After the imaging, you will be brought to a room to rest while the doctors and medical physics team prepare the computer plan. That may take approximately 45 minutes to an hour. Next, you will be brought to the treatment room.

During treatment:

  • You will not need to be put to sleep. You will get medicine to help you relax. The treatment itself does not cause pain.
  • You lie on a table that slides into a machine that delivers radiation.
  • The head frame or face mask aligns with the machine, which has a helmet with holes to deliver small precise beams of radiation directly to the target.
  • The machine may move your head slightly so that the energy beams are delivered to the exact spots that need treatment.
  • The health care providers are in another room. They can see you on cameras and hear you and talk with you on microphones.

The treatment delivery takes anywhere from 20 minutes to 2 hours. You may receive more than one treatment session. Most often, no more than 5 sessions are needed.

Why the Procedure is Performed

Highly focused radiation beans using the Gamma Knife system target and destroy an abnormal area. This minimizes damage to nearby healthy tissue. This treatment is often an alternative to open neurosurgery with surgical cuts.

Gamma Knife radiosurgery can be used to treat the following types of brain tumors or upper spine tumors:

  • Cancer that has spread (metastasized) to the brain from another part of the body
  • A slow-growing tumor of the nerve that connects the ear to the brain (acoustic neuroma)
  • Pituitary tumors
  • Other growths in the brain or spinal cord (chordoma, meningioma)

Gamma Knife is also used to treat other problems of the brain:


Radiosurgery (or any type of treatment), may damage tissue around the area being treated. Compared with other types of radiation therapy, some believe that Gamma Knife radiosurgery, because it delivers pinpoint treatment, is less likely to damage nearby healthy tissue.

After radiation to the brain, local swelling, called edema, may occur, sometimes months after the procedure. You may be given medicine before and after the procedure to lower this risk, but it is still possible. Swelling usually goes away without further treatment. In rare cases, hospitalization and surgery with incisions (open surgery) is needed to treat the brain swelling caused by the radiation.

There are rare cases of swelling causing patients to have problems breathing, and there are reports of fatalities after radiosurgery.

While this type of treatment is less invasive than open surgery, it still has risks. Talk with your provider about the potential risks of treatment and of the risks for tumor growth or spreading.

The skin wounds and locations where the head frame is attached to your scalp may be red and sensitive after treatment. This should go away with time. There may be some bruising.

Before the Procedure

The day before your procedure:

  • DO NOT use any hair cream or hair spray.
  • DO NOT eat or drink anything after midnight unless told otherwise by your doctor.

The day of your procedure:

  • Wear comfortable clothing.
  • Bring your regular prescription medicines with you to the hospital.
  • DO NOT wear jewelry, makeup, nail polish, or a wig or hairpiece.
  • You will be asked to remove contact lenses, eyeglasses, and dentures.
  • You will change into a hospital gown.
  • An intravenous (IV) line will be placed into your arm to deliver contrast material, medicines, and fluids.

After the Procedure

Often, you can go home the same day of treatment. Arrange ahead of time for someone to drive you home, because the medicines you are given can make you drowsy. You can go back to your regular activities the next day if there are no complications, such as swelling. If you have complications, or your doctor believes it is required, you may need to stay in the hospital overnight for monitoring.

Follow instructions given to you by your nurses for how to care for yourself at home.

Outlook (Prognosis)

The effects of Gamma Knife radiosurgery may take weeks or months to be seen. The prognosis depends on the condition being treated. Your provider will monitor your progress using imaging tests such as MRI and CT scans.

Alternative Names

Stereotactic radiotherapy; Stereotactic radiosurgery; SRT; SBRT; Fractionated stereotactic radiotherapy; SRS; Gamma Knife; Gamma Knife radiosurgery; Non-invasive neurosurgery; Epilepsy - Gamma Knife


Brown PD, Jaeckle K, Ballman KV, et al. Effect of radiosurgery alone vs. radiosurgery with whole brain radiation therapy on cognitive function in patients with 1 to 3 brain metastases: a randomized clinical trial. JAMA. 2016;316(4):401-409. PMID: 27458945

Bush A, Vallow L, Ruiz-Garcia H, Herchko S, Reimer R, Ko S, May B, Trifiletti DM, Peterson J. Mask-based immobilization in Gamma Knife stereotactic radiosurgery. J Clin Neurosci. 2021;83:37-42. Epub 2020 Dec 15. PMID: 33339692

Dewyer NA, Abdul-Aziz D, Welling DB. Radiation therapy of benign tumors of the cranial base. In: Flint PW, Francis HW, Haughey BH, et al, eds. Cummings Otolaryngology: Head and Neck Surgery. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 181.

Roque A, Hochberg FH, Baehring JM. Primary nervous system tumors in adults. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 74.

Trifiletti DM, Lee CC, Schlesinger DJ, Sheehan JP. Radiosurgery technique. In: Winn HR, ed. Youmans and Winn Neurological Surgery. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 293.

Review Date 7/17/2022

Updated by: Luc Jasmin, MD, PhD, FRCS (C), FACS, Department of Surgery, Johnson City Medical Center, TN; Department of Surgery St-Alexius Medical Center, Bismarck, ND; Department of Neurosurgery Fort Sanders Medical Center, Knoxville, TN, Department of Neurosurgery UPMC Williamsport PA, Department of Maxillofacial Surgery at UCSF, San Francisco, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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