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.
The 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.
-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.
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.
Unlike the GammaKnife, which is used to treat lesions down to C1, the CyberKnife can be used to treat lesions involving head and neck, lung, kidney, and prostate, as well as all intracranial lesions with the exception of arterial-venous malformations. It can be used for trigeminal neuralgia but requires an invasive imaging study for planning purposes. The CyberKnife provides the ability to fractionate radiation doses and offers CT image-based planning, Dr. Daspit said. You can track the exact location of the patient for accuracy purposes during the treatment, he added.
-P. Ashley Wackym, MD
Dr. Daspit had no financial ties to disclose regarding this device, and he noted that both the GammaKnife and CyberKnife are available at the Barrow Institute.
If a patient with preserved hearing wants radiosurgery, I strongly suggest using the CyberKnife, he stated.
Hearing loss is noted much more commonly with the GammaKnife; however, experience to date suggests that hearing is more likely to be preserved with the CyberKnife. Dr. Daspit said, It should be stressed that the data are quite ‘young’ and much longer follow-up is required to be able to state categorically that fractionation offers better hearing preservation as well as tumor control.
Overall experience at the University of Pittsburgh utilizing the GammaKnife has been reported to offer tumor control rates in the 90% to 95% range over 15 to 20 years. It is not known whether the CyberKnife results will be comparable, as the data reported from Stanford University are only 10 years old. Hearing preservation rates vary in the literature from 40% to 70%, depending on which series is quoted and which device is utilized. According to the literature, facial nerve injury is low with both platforms-in the <2% range, Dr. Daspit said.
Dr. Daspit pointed out and recommended strongly that all interested physicians obtain and read carefully the most recent practice guidelines published by the International Radiosurgery Association at www.irsa.org , he said.
At Barrow Neurological Institute, the trend favors use of the CyberKnife, because most patients present with serviceable hearing and most patients would rather try to preserve their hearing. Also, many points chose a frameless system. At this point in time, our hearing preservation rates are in the 70% range with the CyberKnife and 40% with the GammaKnife, Dr. Daspit said.
Dr. Daspit again emphasized that more long-term data are required and strongly urged otolaryngologists, otologists, and neurotologists to become actively involved in treating patients.
Current data on stereotactic radiation therapy using contemporary dose regimens of 12-13Gy to the tumor margin were presented by Robert Jackler, MD, who is Sewall Professor and Chair of the Department of Otolaryngology, Head and Neck Surgery at Stanford University. He presented a meta-analysis drawn from dozens of articles in the recent literature. This included a substantial number of patients with follow-up periods greater than five years.
In terms of natural history, 55% of untreated acoustic neuromas demonstrate growth over a three-year period. He said that 90% to 95% of sporadic small tumors are controlled over the long term with stereotactic radiotherapy at current doses. Outcomes are poorer in larger tumors, which have a regrowth rate of 30% and a higher risk of radiation-induced brain injury.
For neurofibromatosis type 2 tumors, control rate is only about 70%, and is possibly even lower in younger patients.
According to reports from 2000 through 2007, in patients with Gardiner-Robinson grade 1 or 2 hearing before radiation, there is a 60% chance of preservation at five years, he continued. Hearing preservation is possible in only about 35% of patients with neurofibromatosis type 2, he added.
Facial palsy is rare with current stereotactic radiotherapy doses, although transient facial twitch was reported in a small percent of patients six to eight months following treatment. The primary risk of facial injury occurs when surgery is used following recurrences after stereotactic radiotherapy, Dr. Jackler commented.
Surgical salvage of radiation failure carries a higher complication rate than primary surgery. The converse is not true, however, as radiation salvage of surgical remnants works as well as primary stereotactic radiation. This has led to the exploration of combined therapy, in which large tumors are subtotally removed and the remnant radiated if it shows growth over time.
-Robert Jackler, MD
Secondary malignancy after stereotactic radiotherapy remains a concern, but Dr. Jackler suspects that the incidence is likely to be low. Nevertheless, whenever considering radiation for a benign tumor, the potential of inducing a lethal malignancy years later must be discussed with the patient. Longer-term follow-up is needed to determine the actual incidence of lethal malignancy.
©2008 The Triological Society