WASHINGTON, DC-Stereotactic radiotherapy of the skull base and head and neck is increasingly gaining favor as an attractive alternative to conventional surgery. The technique has the advantages of being noninvasive and the ability to accurately deliver doses of radiation to a target-killing dividing cells, damaging the DNA of cells leading to apoptosis, and reducing the blood supply to tumors, limiting their growth. A panel of experts discussed current experience with stereotactic modalities in otolaryngology practices as well as potential uses. Panelists agreed that optimal candidates still need to be defined for these procedures, but that this treatment option provides an opportunity for participation and leadership among otolaryngologists.
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January 2008The Gamma Knife® is being used at select institutions to treat the following lesions: vestibular schwannomas (acoustic neuromas), other schwannomas or neuromas, meningiomas, head and neck malignancies, and paragangliomas (glomus jugulare tumors), said P. Ashley Wackym, MD, John C. Koss Professor and Chairman of the Department of Otolaryngology and Communication Sciences at the Medical College of Wisconsin in Milwaukee.
This method relies on fixation of a rigid metal frame to the patient’s head using local or general anesthesia. Imaging of the operative field with magnetic resonance (MR) or MR and CT is performed and images are sent to the GammaKnife computer workstation. Treatment of the tumor occurs in the three-dimensional area of the tumor, using spheres of various diameters of radiation designed to conform to the target. Dr. Wackym said the new Gamma Knife Perfexion® now allows treatment of lesions down to the level of the clavicle.
It has been shown that there is a statistically significant reduction in tumor size over time after treatment with Gamma Knife radiosurgery, he said. Also, rare risk factors for growth and malignant transformation need to be defined. Long-term data are needed to determine what ultimate risks are for hearing, balance, and other cranial nerve functions.
At this point in time, our hearing preservation rates are in the 70% range with the CyberKnife and 40% with the GammaKnife.-C. Phillip Daspit, MD
In Dr. Wackym’s experience, most patients treated with the GammaKnife have some reduction in hearing and speech perception, although improvements in both these parameters have been seen over time. Change in vestibular function over time is common, and some patients need vestibular rehabilitation therapy to minimize symptoms and maximize outcomes.
Gamma Knife radiosurgery is performed in a multidisciplinary manner. Regarding the issue of being credentialed to perform the procedure with other team members after appropriate training and experience, Dr. Wackym told listeners, In order to be credentialed as a Gamma Knife surgeon, I would advise working closely with your hospital’s credentialing committee.
CyberKnife
Another platform used to deliver stereotactic radiation therapy is the CyberKnife®, a device that does not require placement of a stereotactic frame and makes use of noninvasive image-guided localization and a robotic delivery system. C. Phillip Daspit, MD, of the Barrow Neurological Institute in Phoenix, described experience with the CyberKnife at his institution. A team approach is used for the treatment of various intracranial and extracranial lesions, including primary brain tumors, metastatic brain lesions, and vestibular schwannomas. Patients are counseled extensively about the various radiosurgery platforms available and are able to decide on which device is best for their particular situation.