What Medical Conditions Can a Gamma Knife Procedure Treat?

Single-dose radiation able to treat certain brain conditions without surgery

Gamma knife radiosurgery
Photo courtesy of Eleckta, Inc.

Gamma Knife radiosurgery is an advanced surgical technique in which a highly focused beam of radiation is used to precisely destroy areas of tissue. Although it is called surgery, a Gamma Knife procedure involves neither incisions nor a scalpel.

The procedure is far less invasive than conventional surgery and offers greater precision when performing delicate operations, primarily on the brain. Because of this, Gamma Knife surgeries can often be performed on an outpatient basis or with an overnight hospital stay.

History

Stereotactic radiosurgery was first developed in 1949 by Swedish neurosurgeon Lars Leskell with the aim of treating small areas of the brain without damaging adjacent tissue.

Leskell’s early designs for the device used X-ray, proton, and later gamma rays to deliver a narrow beam of radiation to a targeted point on the brain. By directing radiation from multiple angles, the converging beams could deliver a lethal dose to destroy tumors, block nerves, or close off blood vessels with minimal collateral damage.

Leskell officially introduced the Gamma Knife in 1968. By the 1970s, the Gamma Knife was fully stereotactic (three-dimensional in approach) with the introduction of magnetic resonance imaging (MRI) and computed tomography (CT) scans. The first Gamma Knife was only brought the United States in 1979 in an arrangement between Leskell and the University of California, Los Angeles.

The Gamma Knife is today the registered trademark of Elekta Instruments, Inc.

in Stockholm, Sweden.

Similar Radiosurgical Devices

In addition to the Leskell device, a similar tool called a linear particle accelerator (Linac) was invented in 1952 as a form of fractionated (multi-dose) radiation therapy. It was only in 1982 that refinements to the device allowed it to be used in radiosurgery.

The Linac device differs from the Gamma Knife in that it is used primarily for radiation therapy in multiple parts of the body. The Gamma Knife, by contrast, is used almost exclusively for the brain radiosurgery. Moreover, the Linac device requires far greater technology and expertise if used for radiosurgery and delivers a far wider beam compared the Gamma Knife (1.1 millimeters versus 0.15 millimeter, respectively).

A newer concept called the Linac Cyberknife was introduced in 2001 and largely mimics the Gamma Knife in concept. The device, mounted on a robotic arm, delivers targeted radiation from multiple angles but, unlike the Gamma Knife, has not demonstrated improved survival rates when compared to other forms of cancer radiation therapy.

A final type of radiosurgery, known at proton beam therapy (PBT), uses a beam of proton particles to irradiate diseased tissue. However, a 2012 study from the American Society of Radiation Oncology concluded that PBT offered no benefits over conventional forms of radiation therapy with the exception of pediatric cancers of the central nervous system, severe eye melanoma, and chordomas (a type of bone cancer).

Despite the potential benefits of PBT, the exceptional cost of the system (between $100 to $180 million) makes it an impractical option for most hospitals.

Conditions Treated

Gamma Knife radiosurgery is most often used to treat tumors and other lesions in the brain. But it can also be effective in treating certain pain and movement disorders as well as vascular abnormalities in the brain.

The Gamma Knife is primarily used to treat the following conditions:

  • Brain metastases (cancers that have spread to the brain from tumors in other organs)
  • Glioblastoma (a type of brain cancer)
  • Acoustic neuroma (a noncancerous tumor on the nerve leading from the inner ear to the brain)
  • Meningioma (a typically noncancerous tumor that arises from the membranes surrounding the brain and spinal cord)
  • Pituitary adenoma (a noncancerous tumor of the pituitary gland)
  • Cushing's disease (a pituitary abnormality in which the body produces too much of the stress hormone, cortisol, due either to benign tumors or steroid drugs like prednisone)
  • Trigeminal neuralgia (a condition in which pressure on the trigeminal nerve causes extreme facial pain)
  • Essential tremor (a neurological disorder that causes involuntary and rhythmic shaking, unrelated to Parkinson's disease)
  • Arteriovenous malformation, or AVM (the abnormal connection between arteries and veins, usually in the brain or spine)

Gamma Knife radiosurgery may be used in situations where the brain lesion cannot be reached by conventional surgery or in persons who cannot tolerate an open surgical procedure such as craniotomy.

Because the beneficial effects of a Gamma Knife procedure manifest slowly over time, it is not used for people whose condition requires immediate or urgent treatment.

How It Works

The Gamma Knife procedure is called a "surgery" because it can be performed in one session with the same clinical aims of a regular operation. The effects of the Gamma Knife differs by the type of disease being treated:

  • When used to treat tumors, the focused radiation disrupts the DNA in tumor cells. This interferes with cell's ability to replicate, causing the tumor to shrink.
  • When used to treat neurological disorders, the beam of radiation causes the formation of a lesion that blocks nerve signals.
  • When used to treat AVM, the Gamma Knife can reduce the size and volume of blood flowing through a vessel, thereby reducing the risk of a rupture or stroke.

The machine itself is similar in design to an MRI or CT scan with a flat bed and a tube-like dome into which your head is placed. It is not as deep as the other machines, however, and is completely silent so that you are less likely to experience claustrophobia.

What to Expect

A Gamma Knife procedure typically involves a treatment team, including a radiation oncologist (a cancer doctor specializing in radiation), a neurosurgeon, a radiation therapist, and a registered nurse. The procedure can differ slightly depending on the treated condition but is usually performed in the following steps:

  1. When you arrive for treatment, you would be asked to lie down on the flat bed after which either a mesh-like mask or a lightweight head frame would be used to stabilize your head and keep it from moving.
  2. An MRI or CT scan would then be performed to pinpoint the exact location and dimensions of the targeted structure or abnormality.
  3. Based on the results, the team will formulate a treatment plan including the precise number of exposures and beam placement.
  4. After being positioned in place, your head would be moved into the dome, and the radiation treatment would begin. You would be fully awake and connected to your doctors through an audio connection. Depending on the condition, the procedure could take anywhere from a few minutes to more than an hour.

Treatment Side Effects

While the Gamma Knife procedure itself is painless, the use of radiation can sometimes cause side effects due mainly to brain inflammation. The severity of symptoms tends to be associated with the duration and location of the radiation treatment and may include:

  • Headache
  • Numbness
  • Nausea
  • Blurry vision
  • Weakness
  • Loss of balance
  • Hair loss (usually temporary)
  • Seizures

There may be other risks associated with your specific medical condition. Be sure to speak with your doctor about this before undergoing a Gamma Knife procedure.

Effectiveness

Gamma Knife radiosurgery has proven effective in treating benign or malignant tumors up to four centimeters (roughly 1½ inches) in size. For people with metastatic brain cancer, the procedure is seen to be effective in providing tumor control and extending survival times.

Success rates vary by the condition being treated, as follows:

  • With regards to AVM, radiosurgery is considered the primary form of treatment today and has a cure rate of between 54 percent and 92 percent depending on the location of the vessel.
  • Meanwhile, a 2016 study from Europe reported that people with trigeminal neuralgia benefited significantly from the procedure, with 71.8 percent remaining pain-free for three years and 45.3 percent remaining pain-free for over 10.
  • Similarly, a 2012 review of clinical studies reported that 88.3 percent of people treated for essential tremors maintained good-to-excellent motor control after 24 months.
  • A 2013 study from the University of Virginia School of Medicine demonstrated that the Gamma Knife procedure afforded a 98 control over tumors associated with Cushing's disease for the duration of the four-year study.

Acute complications following Gamma Knife radiosurgery are considered rare, with most related to the underlying condition rather the procedure itself.

Sources:

Ohye, C.; Higuchi, Y.; Shibazaki. T. et al. "Gamma knife thalamotomy for Parkinson's disease and essential tremor: A prospective multicenter study." Neurosurgery. 2012; 70(3):526-35. DOI: 10.1227/NEU.0b013e3182350893.

Park, H.; Wang, E.; Ruffer, C. et al. "Changing practice patterns of Gamma Knife versus linear accelerator-based stereotactic radiosurgery for brain metastases in the US." J Neurosurg. 2016; 124(4):1018-1024. DOI: 10.3171/2015.4.JNS1573.

Plasencia, A. and Santillan, A. "Embolization and radiosurgery for arteriovenous malformations." Surg Neurol Int. 2012; 3(Suppl 2): S90–S104. DOI: 10.4103/2152-7806.95420.

Regis, J.; Tuleasca, C.; Ressequier, N. et al. "Long-term safety and efficacy of Gamma Knife surgery in classical trigeminal neuralgia: a 497-patient historical cohort study." J Neurosurg. 2016; 124(4):1079-87. DOI: 10.3171/2015.2.JNS142144.

Sheehan, J.; Xu, Z.; Salvetti, D. et al. "Results of gamma knife surgery for Cushing's Disease." J Neurosurg. 2013; 199(6):468-92. DOI: 10.3171/2013.7.JNS13217.

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