Stereotactic Radiosurgery for Vestibular Schwannomas: A Survey of Current Practice Patterns of Neurotologists

Delayed Facial Nerve Dysfunction Following CyberKnife® Radiosurgery for Vestibular Schwannoma

OBJECTIVE

The incidence and risk factors for facial nerve dysfunction (FND) following CyberKnife® therapy for vestibular schwannoma (VS) remain poorly understood. This study investigates whether differential radiation doses to vulnerable segments of the facial nerve may be associated with FND outcomes.

METHODS

Patients were identified who underwent CyberKnife® radiosurgery for VS at a single institution. Basic demographics, tumor characteristics, and facial nerve function were collected. Total radiation doses to tumor, internal auditory canal (IAC), and labyrinthine segment of facial nerve (LSFN) were evaluated.

RESULTS

Six out of 64 patients experienced FND following CyberKnife® treatment for VS (9.38%, 6/64). Patients with FND were compared to those without FND (control). Of the 64 patients, complete radiation records were obtained for 30 patients (6 FND vs. 24 control). There were no significant differences in demographic or tumor characteristics between control and FND cohorts. More severe FND (HB ≥ 4) had significantly larger tumors (3.74 vs. 1.27 cm3, p = 0.037) with directionally decreased time to FND (3.50 vs. 33.5 months, p = 0.106) than patients with HB < 4, respectively. There were directionally, nonsignificant differences between maximum radiation doses to the LSFN (2492.4 vs. 2557.0 cGy, p = 0.121) and IAC (2877.3 vs. 2895.5 cGy, p = 0.824) between the control and FND cohorts, respectively.

CONCLUSIONS

FND may represent an underrecognized sequelae of CyberKnife® radiosurgery for VS that can occur many months following treatment. Further studies are needed to elucidate the effect of differential radiation exposure to the facial nerve with FND following treatment.

LEVEL OF EVIDENCE

3 (Retrospective Cohort Study) Laryngoscope, 134:5080-5086, 2024.

Stereotactic Radiosurgery and Radiotherapy for Vestibular Schwannoma in NF2-Related Schwannomatosis

OBJECTIVES

To determine the long-term control rates and hearing outcomes for growing vestibular schwannoma in NF2-related schwannomatosis (NF2) treated with stereotactic radiosurgery (SRS) and fractionated radiotherapy (FRT).

METHODS

Retrospective review of all patients treated with SRS/FRT between 1986 and2021 from a tertiary NF2 unit. Overall tumor control was defined as: (1) growth control (growth failure was defined as growth in any dimension of 3 millimetres or more from baseline post-SRS/FRT), and (2) treatment control (no need for further intervention). Loss of serviceable hearing was defined as a drop in speech discrimination score below 50% after SRS/FRT.

RESULTS

There were 81 cases, with a mean duration of follow-up of 125 months. Overall control rate was 72% (58/81), with 80% (65/81) growth control and 74% (60/81) treatment control. There was a 5-year actuarial survival of 77% and 10-year survival of 71%. Forty-three percent (30/69) of cases did not have serviceable hearing at baseline. Of those remaining, 49% (19/39) preserved serviceable hearing during follow-up at a mean of 106 months. Actuarial survival for preservation of serviceable hearing at 5 and 10 years was 69% and 53%. There were poorer outcomes with increasing genetic severity, and with baseline tumor size >3 cm. No cases of SRS/FRT-related malignancy were identified at a mean follow-up of 10 years.

CONCLUSION

Stereotactic radiosurgery/fractionated radiotherapy are an effective option to treat growing vestibular schwannoma in patients with NF2 with the potential for hearing preservation in a proportion of patients.

LEVEL OF EVIDENCE

4-Case Series Laryngoscope, 134:2364-2371, 2024.

CyberKnife Stereotactic Radiosurgery for Growing Vestibular Schwannoma: Longitudinal Tumor Control, Hearing Outcomes, and Predicting Post-Treatment Hearing Status

OBJECTIVES

(1) To determine tumor control rates for treating growing vestibular schwannoma (VS) with CyberKnife stereotactic radiosurgery (CK SRS); (2) to determine hearing outcomes after CK SRS; (3) to propose a set of variables that could be used to predict hearing outcomes for patients receiving CK SRS for VS.

STUDY DESIGN

Retrospective case series review.

METHODS

127 patients who received CK SRS for radiographically documented growing VS were reviewed. Tumors were monitored for post-procedure growth radiographically with linear measurements and three-dimensional segmental volumetric analysis (3D-SVA). Hearing outcomes were reviewed for 109 patients. Cox proportional hazard modeling was used to identify variables correlated with hearing outcomes.

RESULTS

Tumor control rate was 94.5% for treating VS with CK SRS. Hearing outcomes were categorized using the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) classification system. As of their last available audiogram, 33.3% of patients with pre-treatment class A and 26.9% of patients with class B retained their hearing in that class. 15.3% of patients starting with class A or B with extended follow-up (>60 months), maintained hearing within this same grouping. Our final model proposed to predict hearing outcomes included age, fundal cap distance (FCD), tumor volume, and maximum radiation dose to the cochlea; however, FCD was the only statistically significant variable.

CONCLUSION

CK SRS is an effective treatment for control of VS. Hearing preservation by class was achieved in a third of patients. Finally, FCD was found to be protective against hearing loss.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:S1-S12, 2024.

Impact of Demographics and Clinical Features on Initial Treatment Pathway for Vestibular Schwannoma

OBJECTIVE

To identify demographic and clinical features impacting initial treatment pathway for vestibular schwannoma.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary care academic medical center.

PATIENTS

Patients diagnosed with vestibular schwannoma between 2009 and 2019.

INTERVENTIONS

Observation, stereotactic radiosurgery, or microsurgical resection.

MAIN OUTCOME MEASURES

χ 2 Test, one-way analysis of variance, and multivariate logistic regression were used to correlate demographic and clinical factors with initial treatment pathway for 197 newly diagnosed vestibular schwannoma patients.

RESULTS

Among 197 patients, 93 (47%) were initially treated with observation, 60 (30%) with stereotactic radiation (Gamma Knife) and 44 (22%) with surgical resection. Age univariately had no statistically significant impact on initial pathway, but those undergoing surgery trended toward a younger demographic (49.1 yr [surgery] versus 57.2 yr [observation] versus 59.0 yr [Gamma Knife]). Men were more likely to be initially observed than women ( p = 0.04). Patients initially observed were more likely to have a lower Koos classification ( p < 0.001) and have better tumor-ear hearing ( p = 0.03). Only 34.4% of patients living outside the local geographic region were initially observed compared with 53.0% living locally ( p = 0.055). Surgeon correlated with initial treatment ( p = 0.04) but did not maintain significance when adjusting for hearing level or tumor size. A multiple linear regression model found age, maximum tumor diameter, and Koos class to correlate with initial treatment pathway ( p < 0.0001, r2 = 0.42).

CONCLUSION

Initial treatment pathway for newly diagnosed vestibular schwannoma is impacted by demographic factors such as age, sex, and geographic proximity to the medical center. Clinical features including hearing level and tumor size also correlated with initial treatment modality.

The changing landscape of vestibular schwannoma diagnosis and management: A cross-sectional study

OBJECTIVES

To assess the current state of the diagnosis and management of vestibular schwannoma (VS) as well as treatment trends, and to evaluate the role of treatment setting and various specialists in treatment plan.

METHODS

Patients diagnosed with VS completed a voluntary and anonymous survey. The questionnaires were distributed through Acoustic Neuroma Association website, Facebook page, and e-mail newsletters from January to March 2017.

RESULTS

In total, 789 VS patients completed the survey. Of those, 414 (52%) underwent surgery; 224 (28%) underwent radiotherapy; and 121 (15%) were observed. General otolaryngologists diagnosed 62% of responders, followed by primary care (11%) and neurotologists (10%). Patients who underwent surgery were significantly younger and had larger tumors compared to those treated with radiation or observation. The ratio of patients having nonsurgical versus surgical resection changed from 1:2 to 1:1 for the periods of 1979 through 2006 versus 2007 through 2017, respectively. Neurosurgeons (40%) and neurotologists (38%) were the most influential in treatment discussion. Neurotologists (P < 0.001) and general otolaryngologists (P = 0.04) were more influential than neurosurgeons for the decision process in patients with smaller tumors. Patients treated at academic versus nonacademic private institutions reported similar tumor sizes (P = 0.27), treatment decisions (P = 0.09), and decision satisfaction (P = 0.78).

CONCLUSION

There is a continuing trend toward nonsurgical management, with approximately half of the patients opting for nonsurgical management. In this cohort, the patients commonly presented with otologic symptoms and otolaryngologists made the most diagnoses. Neurotologists and neurosurgeons were the most influential in treatment discussion.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:482-486, 2020.

Knowledge silos: assessing knowledge sharing between specialties through the vestibular schwannoma literature

OBJECTIVEIt is common for a medical disorder to be managed or researched by individuals who work within different specialties. It is known that both neurosurgeons and neurotologists manage vestibular schwannoma (VS) patients. While overlap in specialty focus has the potential to stimulate multidisciplinary collaboration and innovative thinking, there is a risk of specialties forming closed-communication loops, called knowledge silos, which may inhibit knowledge diffusion. This study quantitatively assessed knowledge sharing between neurosurgery and otolaryngology on the subject of VS.METHODSA broad Web of Science search was used to download details for 4439 articles related to VS through 2016. The publishing journal's specialty and the authors' specialties (based on author department) were determined for available articles. All 114,647 of the article references were categorized by journal specialty. The prevalence of several VS topics was assessed using keyword searches of titles.RESULTSFor articles written by neurosurgeons, 44.0% of citations were from neurosurgery journal articles and 23.4% were from otolaryngology journals. The citations of otolaryngology authors included 11.6% neurosurgery journals and 56.5% otolaryngology journals. Both author specialty and journal specialty led to more citations of the same specialty, though author specialty had the largest effect. Comparing the specialties' literature, several VS topics had significantly different levels of coverage, including radiosurgery and hearing topics. Despite the availability of the Internet, there has been no change in the proportions of references for either specialty since 1997 (the year PubMed became publicly available).CONCLUSIONSPartial knowledge silos are observed between neurosurgery and otolaryngology on the topic of VS, based on the peer-reviewed literature. The increase in access provided by the Internet and searchable online databases has not decreased specialty reference bias. These findings offer lessons to improve cross-specialty collaboration, physician learning, and consensus building.

Effects of CyberKnife therapy for vestibular schwannoma on hearing: a retrospective study

OBJECTIVES

To evaluate the effects of CyberKnife stereotactic radiotherapy for the treatment of vestibular schwannoma on hearing, as evaluated by audiological tests.

METHODS

Patients with vestibular schwannoma were evaluated before and after CyberKnife radiosurgery. Evaluation included pure tone thresholds, speech discrimination scores, auditory brainstem responses and radiological signs.

RESULTS

The study comprised 26 patients diagnosed with vestibular schwannoma and subsequently treated with CyberKnife radiosurgery. The mean follow-up time was 16.4 months. The mean post-treatment hearing preservation rate was 69.23 per cent. There was no significant relationship between hearing loss after treatment and patient age, radiation dosage during treatment, or size of tumour. With regard to auditory brainstem responses, patients with hearing loss following treatment had a significantly higher inter-peak latency between waves I-III than patients with preserved hearing.

CONCLUSION

Stereotactic CyberKnife radiosurgery is an excellent alternative treatment modality for patients with vestibular schwannoma, and results in acceptable preservation of hearing. Residual hearing following CyberKnife therapy is not significantly affected by factors such as age, size of tumour or dosage of treatment.

A Cross-sectional Survey of the North American Skull Base Society: Current Practice Patterns of Vestibular Schwannoma Evaluation and Management in North America

Background  Very few studies have examined vestibular schwannoma (VS) management trends across centers and between providers. The objective of this study is to examine current practice trends, variance in treatment philosophies, and nuanced or controversial aspects of VS care across North America. Methods  This is a cross-sectional survey of North American Skull Base Society (NASBS) members who report regular involvement in VS care. Results  A total of 57 completed surveys were returned. Most respondents claimed to have over 20 years of experience and the majority reported working in an academic practice with an affiliated otolaryngology and/or neurosurgery residency program. Sixty-three percent of respondents claimed to evaluate VS patients in clinic with both an otolaryngologist and neurosurgeon involved. Eighty-six percent of respondents claimed to operate on VS with both an otolaryngologist and neurosurgeon involved, while only 18% of neurosurgeons and 9% of otolaryngologists performed surgery alone. There was a wide range in the number of cases evaluated at each center annually. Similarly, there was wide variation in the number of patients treated with microsurgery and radiation at each center. Additional details regarding management preferences for microsurgery, stereotactic radiosurgery, stereotactic radiotherapy, and conservative observation are presented. Conclusion  VS management practices vary between providers and centers. Overall, most centers employ a multidisciplinary approach to management with collaboration between otolaryngology and neurosurgery. Overall, survey responses concur with previous studies suggesting a shift toward conservatism in management.

CyberKnife for Treatment of Vestibular Schwannoma: A Meta-analysis

Objectives (1) Perform a meta-analysis of the available data on the outcomes of CyberKnife radiosurgery for treatment of vestibular schwannomas (VSs) in the published English-language literature and (2) evaluate the collective outcomes of CyberKnife treatment with respect to tumor control and hearing preservation. Data Sources A thorough literature search of published English-language articles was performed in the PubMed, Ovid, and Cochrane databases. Review Methods A database search was conducted with the keywords "CyberKnife" and "vestibular schwannoma" or "acoustic neuroma." A total of 25 papers were found and reviewed. Data were extracted for patient demographics, number of patients with neurofibromatosis type 2, pretreatment hearing status, tumor size, margin dose, and follow-up duration. The primary outcome variables evaluated were tumor control and hearing preservation. Results After careful review of the published articles, 11 papers reported data on outcomes of CyberKnife treatment for VS and were included in the analysis, comprising 800 patients studied during 1998 to 2012. The reported mean tumor volume ranged from 0.02 to 19.8 cm³, and the follow-up duration ranged from 6 to 120 months. Margin dose varied from 14 to 25 Gy. The collective mean tumor control rate was 96.3% (95% CI: 94.0%-98.5%). The collective hearing preservation rate was 79.1% (95% CI: 71.0%-87.3%) in 427 patients with measurable hearing. Conclusion Clinical data on outcomes of CyberKnife radiosurgery for treatment of VSs are sparse and primarily limited to single-institution analyses, with considerable variation in tumor volume and follow-up time. This meta-analysis not only provides an in-depth analysis of available data in the literature but also reviews reported outcomes and complications.

Dosimetric Analysis of Neural and Vascular Structures in Skull Base Tumors Treated with Stereotactic Radiosurgery

Objective To examine the relationship between the prescribed target dose and the dose to healthy neurovascular structures in patients with vestibular schwannomas treated with stereotactic radiosurgery (SRS). Study Design Case series with chart review. Setting SRS center from 2011 to 2013. Subjects Twenty patients with vestibular schwannomas treated at the center from 2011 to 2013. Methods Twenty patients with vestibular schwannomas were included. The average radiation dose delivered to healthy neurovascular structures (eg, carotid artery, basilar artery, facial nerve, trigeminal nerve, and cochlea) was analyzed. Results Twenty patients with vestibular schwannomas who were treated with fused computed tomography/magnetic resonance imaging-guided SRS were included in the study. The prescribed dose ranged from 10.58 to 17.40 Gy over 1 to 3 hypofractions to cover 95% of the target tumor volume. The mean dose to the carotid artery was 5.66 Gy (95% confidence interval [CI], 4.53-6.80 Gy), anterior inferior cerebellar artery was 8.70 Gy (95% CI, 4.54-12.86 Gy), intratemporal facial nerve was 3.76 Gy (95% CI, 3.04-4.08 Gy), trigeminal nerve was 5.21 Gy (95% CI, 3.31-7.11 Gy), and the cochlea was 8.70 Gy (95% CI, 7.81-9.59 Gy). Conclusions SRS for certain vestibular schwannomas can expose the anterior inferior cerebellar artery (AICA) and carotid artery to radiation doses that can potentially initiate atherosclerotic processes. The higher doses to the AICA and carotid artery correlated with increasing tumor volume. The dose delivered to other structures such as the cochlea and intratemporal facial nerve appears to be lower and much less likely to cause immediate complications when shielded.

Evaluation of Reported Malignant Transformation of Vestibular Schwannoma: De Novo and After Stereotactic Radiosurgery or Surgery

OBJECTIVE

To critically analyze each reported case of malignant transformation of vestibular schwannoma (VS) after either stereotactic radiosurgery (SRS) or microsurgery (MS).

DATA SOURCES

We searched the Pubmed/Medline database using the relevant key words vestibular schwannoma, acoustic neuroma, malignant, transformation, radiation, induced, stereotactic, radiosurgery, malignancy, GammaKnife, and CyberKnife and combinations thereof.

STUDY SELECTION

Inclusion criteria for malignant transformation of VS after SRS included histopathology of initially benign VS, subsequent histopathology confirming malignant VS, reasonable latency period between malignancy and benign diagnoses.

DATA EXTRACTION

A neurotologist and a skull base neurosurgeon independently assessed each case report for quality, entry, exclusion criteria, and comparability of extracted data.

DATA SYNTHESIS

We calculated median age, latency times, and survival times for each case report.

RESULTS

Malignant transformation has been documented to occur after either SRS or MS. Eight cases were included that showed histopathologic evidence of malignant transformation after SRS and MS. Four cases of malignant transformation were included that demonstrated malignant transformation after MS only. Malignant transformation of VS can also occur de novo, and de novo malignant VSs are also encountered, which can confound a causal inference from either SRS or MS. Eighteen cases of primary malignant VS were included. Studies that were identified but not included in the review are summarized and tabulated. We found 12 studies of malignant transformation associated with NF2.

CONCLUSION

The potential mechanism leading to malignant transformation of VS seems more obvious for SRS and is less understood for MS. Given a low incidence of de novo malignant schwannoma, the possibility that these are spontaneous events in either setting cannot be ruled out. Risk of malignant transformation of VS after either SRS or MS is not zero; however, the magnitude of this risk is probably minimal based on the evidence from eight histopathologically confirmed cases.

Vestibular Schwannoma Excision in Sporadic versus Neurofibromatosis Type 2 Populations

OBJECTIVE

To understand the differences in characteristics of neurofibromatosis type 2 (NF2) and sporadic patients with surgically excised vestibular schwannomas in the state of California.

STUDY DESIGN

Cross-sectional.

SETTING, SUBJECTS, AND METHODS

The records of all patients who underwent vestibular schwannoma excision between 1997 and 2011 were extracted from the California Hospital Inpatient Discharge Databases (CHIDD). NF2 cases were identified using ICD-9-CM diagnosis code 237.72, neurofibromatosis, type 2. All other cases were recoded as sporadic. Trends in total number and population-adjusted rates (per 1 million California residents) of surgery, demographics, hospital case volume, state of residency, complications, length of stay, total charges, expected source of payment, and disposition were examined.

RESULTS

Vestibular schwannoma (VS) excision was performed on 7017 patients, of which 464 patients (6.6%) had NF2. The population-adjusted surgery rate declined from 11.8 to 6.2 (P < .001) for sporadic cases and from 0.3 to 0.2 (P = .01) for NF2 cases over the study period. NF2 was associated with younger age (mean, 32.9 vs 51.3), higher rate of other complications (8.8% vs 4.4%) and facial nerve complications (32.3% vs 16.8%), higher total charges (median $70,106 vs $46,395), longer stay (median 5 vs 4), and high volume hospitals (80.4% vs 48.8%) (all P < .001).

CONCLUSION

The surgery rates for vestibular schwannoma excision for both sporadic and NF2 patients have declined, but the decline is more prominent for sporadic cases. NF2 patients tend to be younger and have a longer hospitalization and possibly higher corresponding hospital charges compared to patients with sporadic VS.

Complications of Surgery for Sporadic Vestibular Schwannoma

Objectives

We sought to investigate the postoperative complications of vestibular schwannoma excision and determine their significant clinical predictors.

Study Design

Cross-sectional.

Setting

California Hospital Inpatient Discharge Datasets 1997-2011.

Subjects and Methods

Data for vestibular schwannoma excisions performed in California were extracted using the ICD-9-CM code “04.01 excision of acoustic neuroma.” Demographics, principal payer, state of residence, comorbidities, as well as hospital case volume were examined as possible predictors. Postoperative complications and patient disposition were examined as outcome variables. Comorbidities and complications were identified using ICD-9-CM diagnoses and procedures codes.

Results

Overall, 6553 cases were examined. Comorbidities were present in 2539 (38.7%) patients. Postoperative complications occurred in 1846 (28.2%) patients; 1714 (26.2%) neurological and 337 (5.1%) medical complications. Patients’ admission ended with death or further care (ie, skilled nursing facilities) in 260 (4.0%) cases. Mortality rate was 0.2%. No significant changes were observed over time. Multivariate analysis revealed that the odds of neurological complications were greater in the 2007-2011 period (OR = 1.51; 95% CI, 1.12-2.04), in patients with comorbidities (OR = 1.48; 95% CI, 1.16-1.88), and in hospitals with low case volume (OR = 1.69; 95% CI. 1.31-2.18). The odds of medical complications were also greater in the 2007-2011 period (OR = 1.69; 95%, CI 1.02-2.80). Female gender, non-Caucasian ethnicity, presence of comorbidities, and low hospital case volume were associated with greater odds of patients requiring further care.

Conclusion

Comorbidities and low hospital case volume were major risk factors for complications. No significant changes in rates of complications from vestibular schwannoma surgery were observed over the 15-year period.

Trends in Demographics, Charges, and Outcomes of Patients Undergoing Excision of Sporadic Vestibular Schwannoma

Objective

To assess demographics, charges, and outcome measures by temporal and volume analysis in the treatment of vestibular schwannoma.

Design

Cross-sectional analysis.

Setting, Subjects, and Methods

The California Hospital Inpatient Discharge Databases from 1996 to 2010.

Results

A total of 6545 cases from 1996 to 2010 were identified. Of these, 86.2% occurred at high-volume centers (HVCs), and the number of annual cases decreased by 28.5%. Patients presenting for surgery were increasingly younger, non-Caucasian, and likely to have comorbidities. Total charges significantly increased over time ( P < .001), with the median total charge in 2006-2010 being $91,338 compared with $38,607.92 in 1996-2000 after adjusting for inflation. Routine discharges (home or residence) were more likely at HVCs (odds ratio [OR] 5.48, P < .001) and less likely if patients had Medicaid (Medi-Cal; OR 0.51, P = .002) or Medicare (OR 0.55, P = .022), were 65 years or older (OR 0.56, P = .025), or had comorbidities (OR 0.54, P < .001). Shorter hospital stays were more likely at HVCs (OR 3.77, P < .001) and less likely if patients had Medicaid (OR 0.36, P < .001) or comorbidities (OR 0.61, P < .001). Lesser total charges were more likely at HVCs (OR 2.12, P = .002) and less likely if patients had comorbidities (OR 0.70, P < .001). Mortality was less likely at HVCs (OR 0.10, P = .011).

Conclusion

The profile of patients undergoing vestibular neuroma excision is changing. Surgical volume is decreasing, suggesting a trend toward more conservative management or stereotactic radiation. Patients are best served at HVCs, where routine discharges, shorter length of stay, decreased mortality, and lower total charges are more likely.

Frameless fractionated stereotactic radiosurgery for vestibular schwannomas: a single-institution experience

Objective: To examine tumor control, hearing preservation, and complication rates after frameless fractionated stereotactic radiosurgery (SRS) in patients with vestibular schwannomas (VS).

Methods: Thirty-seven patients treated with fractionated SRS from 2002 to 2011 were retrospectively analyzed. Ninety-five percent were treated with 25 Gy in five fractions, targeting a median tumor volume of 1.03 cc (range 0.14–7.60).

Results: With a median follow-up of 4.25 years (range, 15 months–9 years), no tumors required an additional treatment resulting in 100% tumor control rate. Radiographic control rate was 91% in 32 patients at a median follow-up of 3 years. Of the 14 patients with serviceable hearing and with audiograms, the hearing preservation rate was 78% at a median follow-up of 18 months. Twenty-six patients with serviceable hearing pretreatment, were evaluated by a phone survey with a hearing preservation rate of 73% at a 5 year median follow-up. There were two cases that developed both new increased trigeminal parasthesias and facial spasms but there were no cases of facial weakness. Patient had 96% of good to excellent satisfaction rate with the treatment at a median follow-up of 5 years.

Conclusion: Frameless fractionated SRS treatment of VS results in good rate of tumor control. Hearing preservation rate and rates of cranial nerve toxicity are comparable to what is reported in the literature. Patients choose this modality because of its non-invasive nature and are generally very satisfied with their long term outcome.