Radiosurgery and Radiotherapy

As the largest neurosurgical center in the Pacific Northwest, the UW has both a LINAC Scalpel® and Gamma Knife®, as well as a neutron cyclotron. Patients are evaluated by our multidisciplinary team of neurosurgeons, neuro-oncologists and radiation oncologists and treated with SRS or SRT, depending on what is best for their specific condition. Examples of diseases and disorders which may be treated with SRS or SRT are AVM's, acoustic neuromas, meningiomas, pineal and pituitary tumors, malignant gliomas, trigeminal neuralgia, essential tremor and movement disorders related to Parkinson’s disease. Additionally, research is ongoing in the treatment of epilepsy and neuro-psychiatric conditions.

UW Gamma Knife® Center
http://www.uwmedicine.org/Facilities/Harborview/CentersOfEmphasis/Neuro/Gamma/

UW Radiation-Oncology Home Page
http://www.radonc.washington.edu/

For more information on SRS or SRT please read the following primer:

Stereotactic radiosurgery and radiotherapy refer to the precise delivery of radiation to targeted areas, such as tumors or AVM's (abnormal tangles of blood vessels), of the brain. They differ from normal radiation regimes in that very little, if any, normal tissue is exposed to the radiation. In general, radiation does not remove the tumor or lesion, but it damages the DNA of the tumor cells. This damaged DNA eventually causes the cells to die, because they cannot reproduce or maintain their function. On the other hand, radiation causes the blood vessels of lesions, such as AVM's, to thicken and close off. The shrinking of a tumor or closing off of a vessel occurs over a period of time and depends on the type of tumor or vascular lesion it is.

The difference between stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) is that in SRS, radiation is delivered at a very high intensity, all at once, to a small area, while in SRT, radiation is given at different times, at lower intensities, to larger areas. In other words, in SRS, you get all the radiation at once, while in SRT, radiation is split up over multiple sessions.

Stereotactic Radiosurgery (SRS)
SRS is a way of treating brain disorders with a precise delivery of a single high dose of radiation in a one-day session. Treatment involves the use of focused radiation beams delivered to a specific area of the brain to treat abnormalities, tumors or other functional disorders. Body stereotactic radiosurgery does not exist because there is no way to immobilize the body to treat a tumor in one session the way the head can be secured. Fractionated stereotactic radiation treatments - which are received over a period of days or weeks - may be administered in the body with the assistance of removable masks and frames that achieve some degree of lesser mobilization. Stereotactic radiosurgery is limited to the head and neck as these areas can be immobilized with skeletal fixation devices that completely restrict the head's movement, permitting the most precise and accurate treatment. Treatment without a skeletal fixation device for a one-session treatment is not recommended because of the high potential for damage to healthy brain tissue, cranial nerves (optic, hearing, etc.) and the brain stem.

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 to healthy brain tissue. Stereotactic radiosurgery is routinely used for brain tumors and lesions. It is generally not used as the primary treatments but rather as additional treatment following surgical biopsy or removal of a tumor or lesion. It can also be used as a boost or adjunct to other treatments for a recurring or malignant tumor or when a tumor is inaccessible by surgical means. In some cases, it may be inappropriate.

There are three basic forms of stereotactic radiosurgery represented by three different technological instrument:

• Particle beam (proton)
• Cobalt60 based (photon)
• Linear accelerator based (photon)

The particle beam or cyclotron is in limited use in the United States. In addition to brain tumors, it also treats body cancers in a fractionated manner. There is not much material available on the technology and outcomes at this time. The particle beam is extremely large and funded by public research.

The cobalt60 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 30 years with substantial research and follow-up backing its treatments and outcomes. The machines utilize multiple sources of radiation, which allows for less damage to healthy tissue and better targeting. Over 170,000 people have received treatment with the Gamma Knife® at this time. These machines are ideal for smaller tumors and lesions and for functional disorders of the brain.

The linear accelerator radiosurgery based machines are also prevalent throughout the world. One benefit of this technology is its ability to easily treat very large tumor volumes by treating over time during cell division. 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 such as LINAC Scalpel® Peacock®, X-Knife®, CyberKnife®, Clinac® and others. These machines can be utilized throughout the body as well as the head and neck.

Stereotactic Radiotherapy (SRT)
The linear accelerator machines use one large, intense radiation beam that is redirected in many "arcs" to lessen the effect on healthy tissue. The linear accelerator machines can perform radiosurgery on larger tumors and can fractionate these treatments over several days, having a flexibility that is not available with other machines. These treatments that are given over time are referred to as fractionated stereotactic radiotherapy (FSR) or SRT. Since the linear accelerator moves during treatment, the degree of precision is less than with cobalt60 machines. On the other hand, linear accelerators can produce radiation of higher intensity than the cobalt60 machines, treat larger tumors and lesions, and deliver this energy safely.

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