Stereotactic radiosurgery (SRS) is a non-invasive treatment that uses dozens of tiny radiation beams to accurately target brain tumors with a single high dose of radiation. Despite its name, SRS is not a surgical procedure and does not require an incision or anesthesia. However, the radiation beams are as small and precise as a scalpel.
A computer uses three-dimensional images from MRI and CT scans to determine the exact dimensions of the tumor. It then calculates the radiation dose to be administered by nearly 200 radiation beams. This allows radiosurgeons target the tumor without affecting delicate structures nearby. SRS can treat multiple lesions in a single procedure.
Because stereotactic radiosurgery is typically done in just one outpatient session, patients are spared from multiple radiation treatments and can return to a normal routine within a few days.
In some cases, additional SRS treatments may be ordered by your oncologist. The single dose of radiation is split into smaller doses, or fractions. This procedure is known as fractionated stereotactic radiosurgery.
Stereotactic radiosurgery is effective for treating tumors in small areas in the head and neck that cannot be reached by surgery. It also can be used on patients who cannot tolerate surgery or have had previous radiation therapy to the brain.
There are several types of SRS systems. MD Anderson uses Gamma Knife®, a photon-based radiosurgery system. Gamma Knife is used to treat:
- Cancer that has metastasized (spread) to the brain, head or neck area
- Tumors in the base of the skull
- Malignant gliomas
- Acoustic neuromas
- Pituitary tumors
Gamma Knife® is a major advance in the field of stereotactic
radiosurgery for certain brain cancer patients. It offers a
non-invasive procedure that can be performed in one session and with
Here's what you should know.
What is a Gamma Knife?
The Gamma Knife is a 30-ton machine that contains a cylindrical cone made of the world's largest piece of tungsten with lead shielding. The machine has 192 Cobalt-60 radiation sources that are shaped by eight sectors that surround the patient's head.
There is a theoretical possibility of choosing from 65,000 combinations of highly focused radiation beams. These can be used to create customized shots that target a particular brain tumor, allowing each shot to be tailored to the shape of the patient's tumor.
In addition, the current Gamma Knife model can treat a larger volume of brain area than previous models, which allows greater cranial reach of tumors located in extreme anatomical locations. It has great accuracy to one-tenth of a millimeter and can reach deep-seated targets.
What is Gamma Knife radiosurgery?
Gamma Knife surgery is actually a form of radiation therapy invented in 1967 by Lars Leksell, a Swedish neurosurgeon. The latest model, Perfexion, has been redesigned and re-engineered, and it is the first fully automated Gamma Knife at MD Anderson.
For the one-day procedure, the patient first has a brain MRI with a head frame placed by a neurosurgeon. Then the Gamma Knife team creates a customized treatment plan, which is delivered to the patient who lies on a sophisticated and highly accurate patient positioning system (PPS). The patient's head is inserted into the cone-shaped tungsten cylinder that delivers highly focused gamma rays around the head.
While the contribution of each ray is relatively small -- allowing for less damage to surrounding healthy cells -- when the multiple rays converge on the tumor, they have great intensity. The Gamma Knife unit also has an audio/visual connection so the patient can be seen and also communicate with the treatment team.
Who is eligible for Gamma Knife radiosurgery?
The brain radiosurgery tumor board is a multidisciplinary team of radiation oncologists, neurosurgeons, neuron-radiologists, a radiation physicist and a nurse. At tumor board meetings, each case is discussed to decide if Gamma Knife radiosurgery is the best option. Radiosurgery is especially important for patients who have no other treatment options, including those not eligible for standard surgical techniques due to illness or advanced age.
The Gamma Knife is considered most effective in the treatment of intracranial tumors (within the cranium and the skull base below the brain) such as:
• Brain metastases (cancer that has spread to the brain from other parts of the body)
• Acoustic neuromas
• Pituitary adenomas
• Gilial tumors
• Skull base tumors
• Upper cervical spine tumor
What is the process?
Generally an outpatient treatment, the surgery consists of four steps:
1. Early morning placement of the Leksell stereotactic coordinate frame, which will hold the patient's head in place during imaging and treatment
2. MRI of the brain, which accurately locates and visualizes the tumor
3. Planning of treatment using a Gamma Planning Computer
4. Treatment, followed by observation in the Post-Anesthesia Care Unit
Depending on the number and complexity of the tumors, the delivery of radiation treatment can take from 15 minutes to several hours. A patient usually can return to a normal routine and activities after 24 hours.
What are the advantages of Gamma Knife surgery?
Because it is non-invasive and no surgical incision is required, the physical trauma and the majority of risks associated with open neurosurgical procedures are avoided. The procedure is recognized worldwide and supported by more than 2,500 peer-reviewed research articles. In addition, more than 50,000 patients are treated with Gamma Knife every year by the approximately 250 machines in use around the world.
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