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Gamma Knife Radiosurgery

The Gamma Knife: a non-invasive treatment

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The Leksell Gamma Knife® Perfexion™ – available at Keck Medical Center of USC in Los Angeles – is an effective, non-invasive alternative to traditional brain surgery. For many conditions, Gamma Knife® Perfexion™ is the most accurate form of stereotactic radiosurgery available. This highly sophisticated technology directs focused radiation to specific targets in the brain, thereby offering patients the highest degree of precision and protection to surrounding areas in the brain. Typically performed in a single outpatient treatment session without general anesthesia, this proven technique helps patients avoid incision, scarring, and long hospital stays while minimizing surgical complications.

More than 800,000 patients worldwide have been safely and effectively treated with the Gamma Knife® for malignant and benign brain tumors (including single and multiple metastases), vascular abnormalities and functional disorders. The Gamma Knife® represents one of the most technologically advanced surgical instruments in use today. The Gamma Knife® Perfexion™ is the latest and most advanced version of the Gamma Knife® machine and available at the USC Stereotactic Radiosurgery Center.

Long recognized for pioneering achievements in the field of stereotactic radiosurgery, USC installed its first Gamma Knife® in 1994 and has more than 20 years of experience using the Gamma Knife® to treat brain tumors and disorders.

Eric Chang, MD, professor and chair of the Department of Radiation Oncology, and Gabriel Zada, MD, MS, assistant professor of clinical neurosurgery lead the program. View additional USC Stereotactic Radiosurgery Center program members here.

For more information on our radiation oncology services, click here.

Second Opinions
Our world-class team, which includes members who are internationally recognized for their work in stereotactic radiosurgery, attracts patients from throughout the country seeking an expert second opinion and treatment. The USC Radiosurgery Center welcomes the opportunity to share our expertise.

This outstanding team evaluates each patient to determine whether Gamma Knife® treatment is the best option. The patient’s medical history is reviewed, along with imaging studies and information provided by the patient’s physician. If Gamma Knife® treatment is not considered appropriate, the team will suggest an alternate treatment option.

Conditions Treated

The Gamma Knife® Perfexion™ can be can be used as an alternative to standard neurosurgery or as an adjuvant therapy for residual or recurrent lesions. Gentle, non-invasive and effective, Gamma Knife® radiosurgery is an ideal treatment choice for several categories of tumors and brain disorders, including:

  • Malignant Tumors, including metastatic tumors (cancer that has spread to the brain), gliomas, chordoma and chondrosarcoma. Gamma Knife® radiosurgery achieves control rates of 80-85 percent of metastatic tumors —essentially comparable to open surgery without the risk of infection, bleeding or complications, or a lengthy hospital stay and convalescence.
  • Benign Tumors, including acoustic neuromas (vestibular schwannomas), meningiomas, pituitary adenomas and craniopharyngiomas Follow-up of ten years demonstrates control rates in more than 90 percent of cases of benign tumors with Gamma Knife® treatment. Fifty-three percent of tumors decrease in size while 40 percent remain stable in size. In some cases, combined treatment with maximal safe tumor resection followed by Gamma Knife® offers the best opportunity for long-term tumor control.
    • Up to 98 percent of acoustic neuroma tumors either decrease in size or remain stable, with near complete facial nerve preservation, at six-year follow-up.
    • Gamma Knife® treatment resulted in effective control in a majority of patients with pituitary adenomas. It was particularly beneficial for residual or recurrent tumors following surgery.
  • Vascular Abnormalities, such as arteriovenous malformations. Complete obliteration of AVMs takes place in 60 to 70 percent of patients within two to three years of Gamma Knife® treatment.
  • Functional Disorders, such as trigeminal neuralgia (also known as tic douloureux or chronic facial pain). Gamma Knife® treatment results in initial pain relief for more than 80 percent of patients and long-term pain relief without medications for 63 percent of patients at four-year follow-up.

Candidates for Gamma Knife® Treatment

The Gamma Knife® is highly effective in controlling tumor growth and targets lesions so exactly that the risk of subsequent damage to healthy tissue is minimized. In certain cases, Gamma Knife® treatment may serve as an adjunct to standard neurosurgical therapy or as the preferred course of treatment when further traditional therapy is not recommended.

Gamma Knife® treatment is often the preferred alternative for patients who are not candidates for conventional neurosurgery or radiation therapy. It also may be recommended as an additional therapy for individuals who have already undergone surgery or radiation and require further treatment.

The Gamma Knife® may also be recommended for patients with the following conditions:

  • Tumors or vascular malformations that are surgically inaccessible
  • Risk factors that make surgery inadvisable
  • Need for an additional dose of radiation following conventional radiation therapy
  • Recurrent tumors
  • Facial pain

How Gamma Knife® Works

The Gamma Knife® Perfexion™ is a highly sophisticated technology that relies on cobalt as its energy source. The gamma radiation emitted is shaped into 192 slim beams that are directed to and converge on a defined target. Because the dose along any single beam is so small, the tissue through which it passes is essentially unharmed. As a result, there is little or no radiation delivered to normal surrounding tissue. However, the precise point where the beams converge – for example, at the tumor site – receives a very high dose of radiation.

The Gamma Knife®, which does not contain a blade nor makes an incision, is a sophisticated, dedicated instrument exclusively designed for the treatment of malignant and benign brain tumors, vascular malformations and trigeminal neuralgia. As a non-invasive treatment, Gamma Knife® surgery offers a low-risk, safe, and cost-effective alternative.

The Gamma Knife® Perfexion™ combines data from three-dimensional computer imaging studies with a stereotactic head frame to precisely focus radiation. It can destroy, arrest or reduce tumors, cause lesions to deteriorate, close arteriovenous malformations, and alter the conducting pain fibers in cases of trigeminal neuralgia.

At the time of treatment, the patient is fitted with a stereotactic head frame, which serves as a measuring guide and helps keep the head in a fixed position to assure maximum treatment accuracy. The frame also helps determine coordinates for targeting the abnormality.

After the frame is attached, the patient receives an MRI, CT or angiographic scan. Data from the imaging study is transferred into the state-of-the-art treatment planning computer, which enables the treatment team – composed of a neurosurgeon, radiation oncologist and radiation physicist – to tailor radiation dose distribution to conform specifically to the lesion volume.

When the treatment plan is created, the patient is placed on the Gamma Knife® couch and precisely positioned. Next, the patient is introduced headfirst into the Gamma Knife®, and treatment begins. Then, the patient is treated with the Gamma Knife® Perfexion™ delivering 192 precisely focused beams of gamma radiation to small targets inside the brain. The 192 single doses of gamma rays converge at the target area and deliver a dose that is high enough to destroy the diseased tissue without damaging surrounding healthy tissue.

Treatment and Follow Up

Gamma Knife® treatment consists of the following steps:

  1. Placement of the head frame: A stereotactic frame will be placed on your head and remain there throughout treatment. The frame is needed as a reference point during treatment planning, and is used to hold your head in the position required for precise treatment. This is usually done with a moderate level of sedation, so there is minimal pain and discomfort involved.
  2. Obtaining Precise Images: MRI, CT scans or angiography (a way to visualize the blood vessels) will be used to obtain images that clearly define where the tumor, AVM or treatment site is located. After the required images are obtained, you can relax while the team reviews them and plans your treatment.
  3. Treatment Planning: Once the images are transferred to the Gamma Knife®’s computer planning system, the team will examine them and accurately define the target. The detailed treatment plan they create will determine how long treatment will take.
  4. Treatment: Once the treatment plan has been carefully checked by the team for precision and safety and has been explained to you, treatment will begin. You will enter the Gamma Knife® room and recline on the couch portion of the unit. The team will position your head and the frame, which directs the radiation to the exact treatment target. The team then conducts treatment in an adjacent room, maintaining contact with you through video and intercom. You may choose to listen to music of your choice. The average treatment time ranges from 20 to 90 minutes. When your treatment is over, the head frame is removed and you can leave the center. Most individuals return to normal activities within a day or two.
  5. Post Gamma Knife® Treatment: Your physician will monitor your treatment results by taking periodic MRI, CT scans or angiography. Keck Medical Center of USC staff will stay in contact with your physician in order to monitor your progress. We are available 24 hours a day to provide further consultation on your case.