Gamma Knife

If you have a brain tumor or neurological disorder located in an especially hard-to-reach area, you may be a good candidate for Gamma Knife radiosurgery. Gamma Knife isn’t actually a knife – instead, it’s a machine that delivers a powerful dose of radiation to a targeted point in the brain. Attacking diseased tissues with extreme precision, this treatment leaves healthy tissues untouched.

Though no incisions are involved, Gamma Knife is considered a form of surgery because it can eliminate tumors with the accuracy of a surgical procedure. Patients reap the benefits of surgery without many of the risks, such as infections, bleeding, and complications arising from anesthesia. Local anesthetic is often the only painkiller required, just as you might receive at the dentist’s office.

Patients who undergo Gamma Knife radiosurgery at Siteman Cancer Center are treated by a multidisciplinary team of highly experienced neurosurgeons, radiation oncologists, nurses, radiation therapists, and medical physicists. Their cases are reviewed and discussed weekly at a neuro-oncology tumor board, where our experts collaborate to find the best solutions possible.

At Siteman, we use the Gamma Knife Icon, the newest and most sophisticated machine available. The Icon is unique because it allows for both framed and frameless treatments. This means that patients can sometimes wear a mesh mask instead of the traditional titanium frame that is used to keep the head still during the procedure.

Siteman houses the only Gamma Knife in eastern Missouri, and our patients come to us from all over the region. Because the procedure only requires one to five treatment sessions at most, it is convenient for many of our traveling patients.

Our facility, operated as Gamma Knife of St. Louis, is staffed in partnership with Barnes-Jewish Hospital, the Washington University School of Medicine in St. Louis, and HealthSouth, now Encompass Health. More than 6,000 patients have received treatment through our program since it opened in 1998.

Gamma Knife at Siteman
Siteman houses the only Gamma Knife in eastern Missouri, and our patients come to us from all over the region.

What is Gamma Knife?

Gamma Knife is a technology that uses radiation from 192 cobalt-60 radiation sources to stop tumor growth or repair lesions inside the brain. If you are receiving the procedure for a cancerous tumor, the radiation will alter the DNA of the tumor cells so they can no longer multiply. After a treatment session, your tumor will shrink slowly over the next few weeks or months.

Gamma Knife delivers a higher dose of radiation than whole-brain radiotherapy, but the dose is broken down into 192 separate beams emitted by the cobalt-60 radiation sources. Each beam is too weak to significantly injure healthy tissue by itself, and passes safely through the brain until it reaches the tumor. All of the beams come together at the tumor or treatment area, producing an intense dose of radiation contained within that specific site. The radiation is directed to the tumor like a magnifying glass reflecting the sun. Your doctors will use advanced imaging technology to make sure the radiation beams are concentrated on the right spot.

Over 70,000 patients around the world benefit from this treatment every year.

What are the benefits of Gamma Knife?

Gamma Knife is safer in the short term than traditional neurosurgery, with a much shorter recovery period and a reduced risk of complications. These are some of the advantages:

  • There are no incisions, which means you are unlikely to get an infection.
  • The process is completed in two to five days and does not require a lengthy stay in the hospital. This keeps costs down.
  • The recovery period is very quick. Patients can return to their ordinary routines the following day if they wish.
  • No healthy brain tissues are touched or harmed.

What conditions does Gamma Knife treat?

The procedure treats a variety of malignant and non-malignant brain lesions, specifically those that are smaller in size. Some of these include:

  • Metastatic brain tumors
  • Acoustic neuromas or schwannomas
  • Meningiomas
  • Pituitary adenomas
  • Craniopharyngiomas
  • Pineal tumors
  • Gliomas
  • Trigeminal neuralgia
  • Pediatric tumors
  • Arterial venous malformations
  • Essential tremor
  • Other conditions

Our team is especially skilled at treating metastatic tumors in the brain. Individuals with metastatic tumors make up the largest percentage of our patients.

When to consider Gamma Knife

Your doctor may recommend Gamma Knife if your tumor is in a location that would be too risky for surgeons to reach. You may also wish to avoid neurosurgery, and its associated risks, if you are older or otherwise unable to tolerate surgery and recovery. In addition, you may be a good candidate for the procedure if your tumor is smaller in size.

The procedure is especially well suited for those who have to travel long distances to Siteman Cancer Center. After coming in for an initial consult with the treatment team, patients can complete treatment in just a few sessions. Having a separate appointment for the initial consult reduces the amount of time patients need to spending traveling back and forth. Instead of having to arrange a lengthy stay near our facility, our patients can return to their hometowns after a short period in St. Louis.

Learn more about temporary lodging options near Siteman Cancer Center.

What happens during Gamma Knife treatment?

During treatment, the patient’s head is kept perfectly still while radiation is beamed to the tumor. Doctors use either a titanium frame or a mesh mask to hold the patient’s head in place. Each device requires a different preparation process.

All imaging happens during a different visit prior to treatment day. Performing imaging in advance gives our doctors the time to interpret images in detail, ensuring that nothing is missed. This is what allows our multidisciplinary team to create personalized treatment plans for each and every patient.

Completing this imaging ahead of time also reduces the amount of time patients need to spend at our facility on treatment day. The imaging appointment takes about an hour and a half.


If a frame will be used, a neurosurgeon attaches it to the patient’s head at four points: two on the forehead and two on the back of the head. The patient will receive local anesthetic to keep the skin numb during this process. It only takes a few minutes.

After the frame is attached, new images are taken of the patient’s brain using an MRI, CT scan, or angiogram. Images must be taken with the frame on in order for the doctors and radiation specialists to see where the tumor is located in relation to the equipment.

The patient lies down on the treatment couch attached to the Gamma Knife. The frame is then connected to the machine, and the patient’s head is kept in position while the radiation is delivered. This process is completely painless, and the machine does not make any noise. Treatment can last anywhere from half an hour to several hours, so patients are encouraged to listen to music, books on tape, podcasts, or whatever else will help to make them comfortable. If you need to use the restroom or take a short break, treatment can be paused until you are ready to resume.

After treatment, the frame is removed. Patients are kept for observation for a brief period of time, but are then discharged to go home the same day.

Gamma Knife Mask
For patients who undergo frameless treatment, a mask will be utilized.


For patients who undergo frameless treatment, the first step in the process is the creation of the mask. The patient lies on the treatment couch with a flexible pillow placed under his or her head and a mesh mask over his or her face. Both pillow and mask are then molded to the patient’s face and head. Patients can breathe normally during this process – the mask has an opening for the nose, and the mesh material allows for air flow.

The mask and mold have to be hardened before they are ready for use. Patients often return home or leave the facility during this time and return a few days later for treatment, although the process could be accelerated if necessary.

The procedure then continues as it normally would. Patients who use a mask typically receive their treatments in a few consecutive sessions, rather than a single one.

Why do some patients get the frame and others get a mask?

The decision to use a frame or a mask often depends on the size or location of the tumor. Larger tumors might require too much radiation to treat safely in one session. The mask – which doesn’t have to be physically attached to the patient’s head – better allows doctors to “fractionate” treatments, or to space them out over a period of days.

However, some tumors are not in locations that could best be served by the mask. In these cases, doctors will recommend the frame.

Sometimes, patients themselves have the opportunity to decide whether they would prefer the frame or the mask. Ultimately, this is a decision that the patient and the treatment team will make together after determining which option would be safest.

Does Gamma Knife cause any side effects?

There are a number of side effects associated with Gamma Knife treatment. Most are not severe and will go away on their own.

Patients may notice the following within 24-48 hours after the procedure:

  • Headache
  • Nausea and/or vomiting
  • Fatigue
  • Redness or tenderness where the frame was attached

Contact your doctor or go to the emergency department if you notice or experience any of the following:

  • A fever of 101 degrees F or higher
  • Seizures
  • Changes in vision

Because it can take several weeks or months for the radiation to take full effect in your brain, some side effects may develop over time. One of these side effects is brain swelling.

Brain swelling sounds alarming, but in these cases, the swelling is not as dangerous or urgent because it develops more gradually. Medications such as corticosteroids can reduce or prevent swelling.

Be sure to speak with your doctor about any concerns you may have. Our nursing staff is also extremely knowledgeable and welcomes questions from patients and family members. We want you to be able to participate fully in your care and to know how best to handle your recovery at home.

What is the recovery process like?

The recovery process for Gamma Knife is much shorter and quicker than recovering from brain surgery, although patients should still try to rest as much as they can in the days following the procedure. Patients are usually able to return to work or their other obligations the day after receiving treatment, but they should be mindful of their limits and take breaks when needed.