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Unformatted text preview: 18 O ncology I ssues September/October 2006 FROM RESEARCH TO PRACTICE Gamma Knife vs. CyberKnife by S. Christopher Hoffelt, MD T he procedure called stereotactic radiosur- gery (SRS) is based on a simple concept. A series of radiation beams converges on a target from various angles (Figure 1). With proper planning, a high dose of radiation is given to a target, usually a tumor, with minimal dose to the surround- ing tissue. Ideally this dosage results in destruction of the tumor while sparing function of crucial organs or tissues adjacent to the treatment area, such as the optic nerve or brainstem. For nearly 100 years, this use of cross-firing beam techniques has evolved to allow treatment for both intracranial and extracranial sites. The most widely accepted use for SRS is still for intracranial disease. SRS is now a standard option for many malignant and benign lesions of the brain, as well as some functional conditions (Table 1). Arguably the best known stereo- tactic radiosurgery unit is the Gamma Knife , manufactured by Elekta. The first Gamma Knife unit in North America was installed at the Univer- sity of Pittsburgh Medical Center in 1987 (Figure 2). As SRS has become an accepted standard for malignant and benign conditions, the Gamma Knife and other SRS systems have become more affordable. Hence, the technol- ogy has expanded beyond primarily university hospitals into private hos- pitals and freestanding centers. The CyberKnife is one notewor- thy example of these newer systems, and resembles the Gamma Knife in more than just half its name. [And despite the namestereotactic radio- surgery is knifeless surgery.] Both systems can effectively and accurately perform SRS for intracranial lesions. The CyberKnife differs from the Gamma Knife by employing real-time X-ray images to guide treatment; and as a result has expanded SRS to sites out- side the brain. A basic understanding of both the Gamma Knife and CyberKnife is crucial for any institution to evaluate the potential for acquiring and support- ing this technology. How Gamma Knife Works Accuracy of the Gamma Knife is achieved by fixation of the patients skull to the treatment table by use of a fixed head frame (see Figure 2). A Gamma Knife treat- ment begins with placement of this head frame, usually by a neurosurgeon, on the morning of treatment. After local anesthetic is applied, four screws are used to tightly secure a rigid metal frame to the patients skull. Once the frame is properly secured, the patient is brought to the CT scanner and fixed to the scanning table in a supine posi- tion. A CT scan is acquired for treat- ment planning, and the patient is then released from the table and awaits treatment....
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