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Centers of ExcellenceStereotactic Radiosurgery Overview

Definition:
Stereotactic radiosurgery (SRS) treats brain disorders with a precise delivery of a single, high dose of radiation in a one-day session. Focused radiation beams are delivered to a specific area of the brain to treat abnormalities, tumors or functional disorders.

Body radiosurgery is rare. We are able in only a few Centers of Excellence to immobilize and treat the body in a radiosurgical fashion, using high-level special technology.

Fractionated stereotactic radiation treatments-which are received over a period of days or weeks-may be administered to the body with the assistance of removable masks and frames that achieve a lesser degree of immobilization. Stereotactic radiosurgery is limited to the head and neck, because these areas can be immobilized with skeletal fixation devices that completely restrict the head's movement, permitting the most precise and accurate treatment. One-session treatment without a skeletal fixation device is not recommended because of the high potential for damage to healthy brain tissue, cranial nerves (optic, hearing, etc.) and the brain stem.

Surgery:
Radiosurgery (one-session treatment) has such a dramatic effect in the target zone that the changes are considered "surgical." Through the use of three-dimensional computer-aided planning and the high degree of immobilization, the treatment can minimize the amount of radiation that passes through healthy brain tissue. Stereotactic radiosurgery is routinely used to treat brain tumors and lesions. It may be the primary treatment, used when a tumor is inaccessible by surgical means; or as a boost or adjunct to other treatments for a recurring or malignant tumor. In some cases, it may be inappropriate.

How it Works:
Stereotactic radiosurgery works the same as all other forms of radiation treatment. It does not remove the tumor or lesion, but it distorts the DNA of the tumor cells. The cells then lose their ability to reproduce and retain fluids. The tumor reduction occurs at the rate of normal growth for the specific tumor cell. In lesions such as AVMs (a tangle of blood vessels in the brain), radiosurgery causes the blood vessels to thicken and close off. The shrinking of a tumor or closing off of a vessel occurs over a period of time. For benign tumors and vessels, this will usually be 18 months to two years. For malignant or metastatic tumors, results may be seen in a few months, because these cells are very fast-growing.

Side Effects:
Swelling: As with all radiation treatments, the cells of the irradiated tumors lose their ability to regulate fluids, and edema or swelling may occur. This does not happen in all treatments. If swelling does occur, and it causes symptoms that are unpleasant, then a mild course of steroid medication may be given to reduce the fluid within the tumor cavity.

Necrosis: The tumor tissue that remains after the radiation treatment will typically shrink. On rare occasions this necrotic or dead tissue can cause further problems and may require removal. This occurs in a very small percentage of cases.

Other Effects: Other side effects may occur dependent upon the target site and the dose of radiation received. This should be discussed throughly with your treating physician. For more information on side effects and radiation injury Click Here.

Is it Appropriate?:
Because all forms of radiation treatments work over time, they may be inappropriate if symptoms are severe or life-threatening. Relief of acute symptoms may drive the first treatment choice to open skull surgery or medication. For instance, if the symptoms at the time of diagnosis are so severe that quality of life is affected, the appropriate choice for the first treatment may be surgery to relieve those symptoms. The secondary treatment could then be radiosurgery.

In other cases where cells are extremely fast growing (with or without severe symptoms), such as in brain metastases, radiosurgery can quickly control the brain tumors to allow time to treat the primary cancer site. Medication can be given for the side effects (such as edema), and radiation therapy may be used over a period of time to help eliminate any stray cancer cells from the brain.

Previous Radiation:
Stereotactic radiosurgery can be used in patients who have failed standard radiation techniques, or in patients who have already received whole brain radiation or the maximum radiation dose permissible. There is little literature on radiation-induced new tumors caused by stereotactic radiosurgery. It is expected that the possibility of developing a tumor is 1 in 10,000 cases. This may be attributed to the precision of the treatment and the sparing of healthy nerves and tissues. A patient who has had stereotactic radiosurgery for a brain tumor or another condition may have open skull surgery later without problems. In many cases, stereotactic radiosurgery can be performed again if necessary.

Types:
There are three basic forms of stereotactic radiosurgery represented by three different technological instruments. Each instrument operates differently, has a different source of radiation and may be more effective under different circumstances. The three are:

  • Particle beam (proton)
  • Cobalt-60 based (photon)
  • Linear accelerator based (linac)

The particle/proton beam exists in a handful of centers in the United States. In addition to brain tumors, it treats body cancers in a fractionated manner. Due to the cost of the particle beam facility (>$100 million), little research is currently available; however, more is expected in the future. Many of the costs of the particle beam are funded by endowments and public research centers.

The cobalt-60 based machines are located at dedicated neuroscience centers in the United States and throughout the world. These machines provide extremely accurate targeting and precise treatment for brain cancers. They are dedicated to treating only brain tumors and dysfunctions in a one-day treatment. The most well-known machine is the Gamma Knife®.

The Gamma Knife® does not move during treatment, thus providing a high degree of precision within the brain. It has been available for over 40 years, with constant enhancements, substantial research and follow-up backing its treatments and outcomes. The unit today is much the same as when it was developed. The machines utilize multiple sources of radiation, which causes less damage to healthy tissue and results in better targeting. Over 350,000 people have received treatment with this machine at this time. These machines are ideal for smaller tumors (less than 3.5 cm) and functional disorders of the brain. The manufacturer's name is Elekta Instruments.

The linear accelerator based radiosurgery machines are also prevalent throughout the world. One benefit of this technology is its ability to easily treat large tumor volumes (over 3.5 cm) by treating over several sessions. When treating over time, it is called fractionated stereotactic radiotherapy and not stereotactic radiosurgery (which is a one-session treatment). The machines are made by multiple manufacturers with common brand names: Novalis Tx®, CyberKnife®, and others. The Novalis Tx® is the most common machine available. Linear accelerator based machines are not dedicated to treatments only within the brain. They can be used throughout the body, as well as the head and neck.

Often, the linear accelerator radiosurgery unit must be set up before a treatment can be given. This occurs after all conventional radiation therapy is completed for the day. At centers where this is done, the number of radiosurgery treatments within the brain performed over a year is not usually high, and therefore, outcomes may not be as good. The linear accelerator based machines utilize one large intense radiation beam that is redirected in many "arcs" to lessen the adverse effects on healthy tissue. Since the linear accelerator moves during treatment, the degree of precision is less than that of cobalt-60 machines. These machines can perform radiosurgery on larger tumors and can fractionate treatments over several days, yielding a flexibility that is not available with other machines. Treatments that are given over time are referred to as fractionated stereotactic radiotherapy (FSR) or stereotactic radiotherapy (SRT). Because multiple manufacturers produce linear accelerator units, data and results are usually not comparable between different units and treating sites, as each type of unit requires different calibrations and adjustments. As a result, there may appear to be a lack of peer-reviewed research available about a diagnosis and treatment.

Indications:
Stereotactic radiosurgery may or may not be appropriate for a condition. It may be used as the primary treatment or recommended in addition to other treatments that are needed. Only a treating neurosurgeon who operates radiosurgery equipment can make the evaluation as to whether someone can be treated. A neurosurgeon must always be present during treatment and should work with a radiation oncologist when the brain is being targeted. Some of the most common indications for treatment are:

Current research areas include epilepsy, headaches and neuro-psycho conditions.

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