Radiotherapy for vestibular schwannoma: Review of recent literature results

Brazilian Society of Otology task force - Vestibular Schwannoma ‒ evaluation and treatment

OBJECTIVE

To review the literature on the diagnosis and treatment of vestibular schwannoma.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on vestibular schwannoma were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: (1) Diagnosis - audiologic, electrophysiologic tests, and imaging; (2) Treatment - wait and scan protocols, surgery, radiosurgery/radiotherapy, and systemic therapy.

CONCLUSIONS

Decision making in VS treatment has become more challenging. MRI can diagnose increasingly smaller tumors, which has disastrous consequences for the patients and their families. It is important to develop an individualized approach for each case, which highly depends on the experience of each surgical team.

Evolution in the management of vestibular schwannoma: a single-center 15-year experience

PURPOSE

To highlight the changes in the management of vestibular schwannoma (VS) since 2004 with a focus on small- to middle-size VS.

METHODS

Retrospective analysis of the decisions made in skull base tumor board between 2004 and 2021.

RESULTS

1819 decisions were analyzed (average age 59.25, 54% females). Overall, 850 (47%) cases were allocated to a Wait and Scan (WS) approach, 416 (23%) received radiotherapy and 553 (30%) were treated surgically (MS). All stages considered WS increased from 39% before 2010 to 50% after 2010. Similarly, Stereotactic Radio Therapy (SRT) increased from 5 to 18%. MS decreased from 46 to 25%. It was more commonly proposed to younger patients and larger tumors, p < 0.001. For Koos stages 1, 2, and 3 there was a statistically significant increase in SRT, and a decrease in MS, p < 0.001. WS also increased for stages 1 and 2. However, such a trend was not observed for stage 3. MS remained the primary treatment modality for stage 4 tumors throughout the study period, p = 0.057. The significance of advanced age as a factor favoring SRT decreased over time. The opposite is true for serviceable hearing. There was also a decrease in the percentage of the justification "young age" in the MS category.

CONCLUSION

The is a continuing trend towards non-surgical treatment. Small- to medium-sized VS witnessed an increase in both WS and SRT. There is only an increase in SRT for moderately large VS. Physicians are less and less considering young age as a factor favoring MS over SRT. There is a tendency towards favoring SRT when hearing is serviceable.

From the perspective of pseudo-progression rather than treatment failure, how long should we wait before considering treatment failure if large cystic enlargement occurs after Gamma Knife radiosurgery for vestibular schwannoma?: insight into pseudoprogression based on two case reports

Gamma knife radiosurgery (GKRS) has been accepted as a safe and effective treatment for vestibular schwannoma (VS). However, during follow-up, tumor expansion induced by irradiation can occur, and diagnosis of failure in radiosurgery for VS is still controversial. Tumor expansion with cystic enlargement causes some confusion regarding whether further treatment should be performed. We analyzed more than 10 years of clinical findings and imaging of patients with VS with cystic enlargement after GKRS. A 49-year-old male with hearing impairment was treated with GKRS (12 Gy; isodose, 50%) for a left VS with a preoperative tumor volume of 0.8 cc. The tumor size increased with cystic changes from the third year after GKRS, reaching a volume of 10.8 cc at 5 years after GKRS. At the 6th year of follow-up, the tumor volume started to decrease, up to 0.3 cc by the 14th year of follow-up. A 52-year-old female with hearing impairment and left facial numbness was treated with GKRS for a left VS (13 Gy; isodose, 50%). The preoperative tumor volume was 6.3 cc, which started to increase with cystic enlargement from the first year after GKRS, and reaching 18.2 cc by 5 years after GKRS. The tumor maintained a cystic pattern with slight changes in size, but no other neurologic symptoms developed during the follow-up period. After 6 years of GKRS, tumor regression was observed, eventually reaching a volume of 3.2 cc by the 13th year of follow-up. In both cases, persistent cystic enlargement in VS was observed at 5 years after GKRS, after which the tumors began to stabilize. After more than 10 years of GKRS, the tumor volume was less than that before GKRS. Enlargement with large cystic formation in the first 3-5 years after GKRS has been considered as treatment failure. However, our cases show that further treatment for cystic enlargement should be deferred for at least 10 years, especially in patients without neurological deterioration, as inadequate surgery can be prevented within that period.

Correlation between initial tumor enlargement and magnetic resonance imaging characteristics following linear accelerator-based stereotactic radiosurgery for acoustic neuromas

BACKGROUND

Initial tumor enlargement (or pseudoprogression) instead of true tumor progression is a common phenomenon in patients with acoustic neuromas who are treated with stereotactic radiosurgery (SRS). This phenomenon can affect clinical decision-making and patient management. This study assessed the correlation between initial tumor enlargement and magnetic resonance imaging characteristics in patients with acoustic neuromas who were treated with linear accelerator (LINAC)-based SRS. The long-term tumor control outcomes were also analyzed.

MATERIALS AND METHODS

In total, 330 patients with sporadic acoustic neuromas who were treated with LINAC SRS between March 2006 and March 2020 were retrospectively evaluated to assess their initial tumor enlargement. The tumors were divided into homogeneously enhanced, heterogeneously enhanced, and cystic types based on the morphological characteristics noted on magnetic resonance images. Tumor control was assessed in 275 patients with a follow-up duration of more than 2 years.

RESULTS

Initial enlargement was observed in 137 of 330 (41.5%) tumors as early as 3 months after LINAC SRS. Data analysis revealed that postoperative tumors with a residual volume lower than 2.5 cm3 had a lower incidence of initial enlargement (p = 0.039). No correlation was noted between the initial enlargement and morphological characteristics of tumors. In patients with a mean follow-up duration of 82.8 ± 37.2 months, heterogeneously enhanced tumors exhibited a lower control rate than homogeneously enhanced and cystic tumors (p = 0.045). No correlation was noted between initial enlargement and tumor control.

CONCLUSION

Initial enlargement can occur as early as 3 months after SRS. Postoperative residual tumors with a volume lower than 2.5 cm3 exhibit a lower incidence of initial enlargement. Heterogeneously enhanced tumors have a lower local control rate.

The role of particle radiotherapy in the treatment of skull base tumors

The skull base is an anatomically and functionally critical area surrounded by vital structures such as the brainstem, the spinal cord, blood vessels, and cranial nerves. Due to this complexity, management of skull base tumors requires a multidisciplinary approach involving a team of specialists such as neurosurgeons, otorhinolaryngologists, radiation oncologists, endocrinologists, and medical oncologists. In the case of pediatric patients, cancer management should be performed by a team of pediatric-trained specialists. Radiation therapy may be used alone or in combination with surgery to treat skull base tumors. There are two main types of radiation therapy: photon therapy and particle therapy. Particle radiotherapy uses charged particles (protons or carbon ions) that, due to their peculiar physical properties, permit precise targeting of the tumor with minimal healthy tissue exposure. These characteristics allow for minimizing the potential long-term effects of radiation exposure in terms of neurocognitive impairments, preserving quality of life, and reducing the risk of radio-induced cancer. For these reasons, in children, adolescents, and young adults, proton therapy should be an elective option when available. In radioresistant tumors such as chordomas and sarcomas and previously irradiated recurrent tumors, particle therapy permits the delivery of high biologically effective doses with low, or however acceptable, toxicity. Carbon ion therapy has peculiar and favorable radiobiological characteristics to overcome radioresistance features. In low-grade tumors, proton therapy should be considered in challenging cases due to tumor volume and involvement of critical neural structures. However, particle radiotherapy is still relatively new, and more research is needed to fully understand its effects. Additionally, the availability of particle therapy is limited as it requires specialized equipment and expertise. The purpose of this manuscript is to review the available literature regarding the role of particle radiotherapy in the treatment of skull base tumors.

Dosimetric predictive factors for facial nerve paralysis after cyberknife® stereotactic radiotherapy for vestibular schwannomas: A single institution experience of 88 patients

PURPOSE

To identify dosimetric predictive factors of facial nerve paralysis for patients with vestibular schwannomas (VS) treated in a single institution with Cyberknife® (CK) hypofractionated stereotactic radiotherapy (SRT).

METHODS AND MATERIALS

Eighty-eight patients were treated from 2010 to 2020. Different treatment schedules were used over that period, some prescribed to the 80% isodose line (4 × 5 Gy, 3 × 7 Gy, 3 × 8 Gy and 5 × 5 Gy) and one to the 70% isodose line (3 × 7.7 Gy). Local control tumor and facial nerve toxicity were recorded, as well as various dosimetric indicators.

RESULTS

Median follow-up 37 months (range, 7-96). Of the 88 stereotactic treatments, 20 patients (23%) developed objectively diagnosed radiation-induced facial nerve paralysis. The 2-year and 5-year local tumor control were respectively 95% and 88%, and the overall 2-year facial nerve preservation was 76%. Prescriptions with a maximum dose point (Dmax) of 33 Gy were at a substantially higher risk of facial paralysis than prescriptions with a Dmax less than or equal to 30 Gy (HR = 4.51, 95% CI = [1.04;19.6], p = 0.045). The 2-years cumulative incidences of facial paralysis were 32% [20%;44%] in the case of a 33 Gy Dmax, against 7% [1%;21%] otherwise. We identified four significative dosimetric predictive factors for radiation-induced facial nerve dysfunction: a GTV minimal dose over 22 Gy (EQD2 = 45.5 Gy, p = 0.019), a GTV mean dose over 29 Gy (EQD2 = 73.5 Gy, HR = 2.84, 95% CI = [1.10;7.36], p = 0.024), a PTV mean dose over 27 Gy (EQD2 = 64.8 Gy, HR = 10.52, 95% CI = [1.39;79.76], p = 0.002) and a PTV maximal dose of 32 Gy (EQD2 = 87.5 Gy,HR = 5.09, 95% CI = [1.17;22.15], p = 0.013).

CONCLUSION

We identified four dosimetric predictive factors for post-treatment facial paralysis. Increasing the doses of hypofractionated stereotactic radiotherapy for vestibular schwannomas leads to higher facial nerve toxicity and may lead to lower local control rates than other published series. Our three-hypofractionated regimens may have also played a role in these results.

Vestibular Schwannoma Hypofractionated Stereotactic Radiation Therapy in Five Fractions

AIM

To retrospectively analyse the long-term results of hypofractionated stereotactic radiation therapy (HSRT) applied in five fractions for vestibular schwannomas.

MATERIALS AND METHODS

One hundred and thirty-four patients with vestibular schwannomas underwent medical treatment of HSRT. The median follow-up time interval was 54 months (range 6-121 months). All patients had a prescribed dose of 22 Gy in five fractions to D90. Restaging was carried out by thin-slice contrast-enhanced T1 magnetic resonance imaging. Progression was defined as 2 mm post-treatment tumour enlargement. Progression or death for any reason was counted as an event in progression-free survival rates. Acute toxicity was defined as adverse events occurring within 3 months of HSRT; long-term toxicity was defined as such events occurring after 3 months.

RESULTS

In 74/128 patients who had >6 months of follow-up (54%), the HSRT resulted in a partial or a complete response. The mean time interval for response in 50% of these was 4 years, whereas in 49 patients (38%) vestibular schwannomas failed to show any response, resulting in stable disease. Five of 128 patients (4%) showed marked progressive vestibular schwannomas after treatment in the first 3 years; two of them received conventionally fractionated radiation therapy. Local control at 3, 5 and 7 years was 96%, 95% and 94%, respectively. Seven were lost to follow-up. The median planning target volume was 2.1 ml (range 0.78-8.66). The 3- and 5-year progression-free survival rates were 95% and 94%, respectively. Seven patients reported a marked deterioration in hearing ability. Post-radiation therapy magnetic resonance imaging showed variability in oedema collection, but no patient suffered from radio-necrosis. Grade 2 temporary facial nerve disorders were observed in 10 patients (8%) 3-6 months after HSRT.

CONCLUSION

Delivering HSRT in five fractions for vestibular schwannoma appears safe and efficient, combining both efficiency and short treatment time while optimising neurological function preservation.

A mechanistic mathematical model of initiation and malignant transformation in sporadic vestibular schwannoma

BACKGROUND

A vestibular schwannoma (VS) is a relatively rare, benign tumour of the eighth cranial nerve, often involving alterations to the gene NF2. Previous mathematical models of schwannoma incidence have not attempted to account for alterations in specific genes, and could not distinguish between nonsense mutations and loss of heterozygosity (LOH).

METHODS

Here, we present a mechanistic approach to modelling initiation and malignant transformation in schwannoma. Each parameter is associated with a specific gene or mechanism operative in Schwann cells, and can be determined by combining incidence data with empirical frequencies of pathogenic variants and LOH.

RESULTS

This results in new estimates for the base-pair mutation rate u = 4.48 × 10^-10 and the rate of LOH = 2.03 × 10^-6/yr in Schwann cells. In addition to new parameter estimates, we extend the approach to estimate the risk of both spontaneous and radiation-induced malignant transformation.

DISCUSSION

We conclude that radiotherapy is likely to have a negligible excess risk of malignancy for sporadic VS, with a possible exception of rapidly growing tumours.

Decision Making on Vestibular Schwannoma: Lessons from a Multidisciplinary Board

BACKGROUND

Management of vestibular schwannoma (VS) is a complex process aimed at identifying a clinical indication for fractionated stereotactic radiotherapy (sRT) or radiosurgery, microsurgical resection, or wait and scan (WS). We describe the experience of our VS multidisciplinary team (MDT) at a tertiary university referral center created for diagnosis, treatment, and follow-up of VS patients.

METHODS

We conducted a retrospective study on 132 consecutive patients referred to the MDT and managed by observation (WS), microsurgery, or fractionated sRT. The analysis included patient age, tumor size, hearing level, facial nerve function, tumor control, complications, and quality of life questionnaires.

RESULTS

Among the patients, 21% were subjected to microsurgery, 10% to sRT, and 69% to WS. The median follow-up time was 30 months. Outcomes based on different management modalities are described. Statistically significant differences among groups were detected in terms of quality of life (physical domain).

CONCLUSIONS

MDT may provide the best individualized therapy for VS patients compared with a single gold-standard strategy.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8-10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

Stereotactic Radiosurgery for Vestibular Schwannoma Outcomes in Patients With Perfect Word Recognition-A Retrospective Cohort Study

OBJECTIVES

To investigate tumor control rate and hearing outcomes following stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) cases with perfect (100%) word recognition score (WRS).

STUDY DESIGN

A retrospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

Inclusion criteria were receiving primary SRS, a pretreatment WRS of 100%, and availability of both pre- and posttreatment audiometric data for evaluation.

INTERVENTION

SRS delivered by Cyberknife.

MAIN OUTCOME MEASURES

Tumor growth rates and audiological outcomes after SRS.

RESULTS

The cohort consisted of 139 patients, with more than 1-year follow-up (mean 6.1 yrs). SRS tumor control rate was 87% for the whole cohort. Growth before SRS was documented in 24% (n = 34 of 139). The proportion of sporadic VS cases who maintained hearing (decline <10 dB of pure-tone audiometry or <20% of WRS) at 3 years was 50%, at 5 years was 45%, and at 10 years was 42%. In multivariate analysis, increased age was found to be predictive of increased hearing loss (p = 0.03), while the following factors were shown not to be significant: sex (p = 0.5), tumor size (p = 0.2), pre-SRS tumor growth (p = 0.5), and target volume (p = 0.42).

CONCLUSIONS

Among patients with VS who had perfect WRS and underwent SRS, the overall tumor control rate was 87% comparable to observation. Hearing maintenance and preservation of "serviceable" hearing rates after 5 years in VS patients with perfect WRS treated by SRS is less than that when comparing to similar observation cohorts. Given this finding we do not advocate using SRS to preserve hearing, over observation, in tumors with perfect WRS.

Efficacy and comorbidities of hypofractionated and single-dose radiosurgery for vestibular schwannomas: a systematic review and meta-analysis

Background

Vestibular schwannomas (VS) are tumors of the cerebellopontine angle with significant morbidity, causing hearing loss, tinnitus, and trigeminal and facial nerve compromise. An effective alternative to microsurgical resection is stereotactic radiosurgery (SRS), which can be delivered in either single-fraction (SRS) or hypofractionated stereotactic radiotherapy (hSRT) (3-5 treatments) regimens. It remains unclear which fractionation regimen provides superior outcomes.

Methods

Ovid MEDLINE, EMBASE, CINAHL, and Cochrane Reviews were searched for studies either comparing hSRT with SRS or focusing on hSRT alone in treating VS. Primary endpoints included tumor control, serviceable hearing, tinnitus, and cranial nerve V and VII symptoms. A random-effects analysis was employed to compare pre- and post-treatment effects (hSRT alone) or SRS and hSRT outcomes (two-arm studies).

Results

This analysis included 21 studies focusing on hSRT alone and 13 studies comparing SRS and hSRT. Significant heterogeneity was observed. Overall, when hSRT was analyzed alone, crude tumor control was achieved in 94% (95% CI: 88%, 99%) of 1571 patients. There was no difference between pre- and post-treatment odds ratios (OR) of tinnitus, facial, or trigeminal impairment. Serviceable hearing was diminished following hSRT (OR = 0.60, 95% CI: 0.44, 0.83). Comparison with SRS showed no difference with respect to tumor control, serviceable hearing, trigeminal or facial nerve impairment.

Conclusions

hSRT achieved excellent tumor control and, with the exception of serviceable hearing, did not result in worse post-treatment cranial nerve symptomatology. Analysis of comparative studies between hSRT and SRS did not reveal any significant difference in either tumor control or treatment morbidities.

Stereotactic Radiosurgery for Vestibular Schwannomas: Tumor Control Probability Analyses and Recommended Reporting Standards

PURPOSE

We sought to investigate the tumor control probability (TCP) of vestibular schwannomas after single-fraction stereotactic radiosurgery (SRS) or hypofractionated SRS over 2 to 5 fractions (fSRS).

METHODS AND MATERIALS

Studies (PubMed indexed from 1993-2017) were eligible for data extraction if they contained dosimetric details of SRS/fSRS correlated with local tumor control. The rate of tumor control at 5 years (or at 3 years if 5-year data were not available) were collated. Poisson modeling estimated the TCP per equivalent dose in 2 Gy per fraction (EQD2) and in 1, 3, and 5 fractions.

RESULTS

Data were extracted from 35 publications containing a total of 5162 patients. TCP modeling was limited by the absence of analyzable data of <11 Gy in a single-fraction, variability in definition of "tumor control," and by lack of significant increase in TCP for doses >12 Gy. Using linear-quadratic-based dose conversion, the 3- to 5-year TCP was estimated at 95% at an EQD2 of 25 Gy, corresponding to 1-, 3-, and 5-fraction doses of 13.8 Gy, 19.2 Gy, and 21.5 Gy, respectively. Single-fraction doses of 10 Gy, 11 Gy, 12 Gy, and 13 Gy predicted a TCP of 85.0%, 88.4%, 91.2%, and 93.5%, respectively. For fSRS, 18 Gy in 3 fractions (EQD2 of 23.0 Gy) and 25 Gy in 5 fractions (EQD2 of 30.2 Gy) corresponded to TCP of 93.6% and 97.2%. Overall, the quality of dosimetric reporting was poor; recommended reporting guidelines are presented.

CONCLUSIONS

With current typical SRS doses of 12 Gy in 1 fraction, 18 Gy in 3 fractions, and 25 Gy in 5 fractions, 3- to 5-year TCP exceeds 91%. To improve pooled data analyses to optimize treatment outcomes for patients with vestibular schwannoma, future reports of SRS should include complete dosimetric details with well-defined tumor control and toxicity endpoints.

Delayed pseudoprogression of a vestibular schwannoma postradiosurgery

Radiosurgery (RS) can offer excellent local control in the management of both benign and malignant tumors measuring less than 3 cm in size. A known late complication of radiosurgery is radiation necrosis which generally occurs within 6-18 months following treatment and has an increased risk of occurrence with higher radiation doses. The lower dose used to treat vestibular schwannomas (VS) makes this complication less frequent. Tumors that do not respond to radiosurgery and continue to grow may require surgical intervention. We report a case of a young male who received radiosurgery (18 Gy in 3 fractions) in February 2016 for a recurrent VS following initial debulking surgery in 2008. Follow-up imaging revealed an interval decrease in size by May 2017; however, by April 2018, there was significant interval increase in the cisternal components of the tumor. By September 2018, the lesion had increased by >50% (to a size of 29 mm) compared to May 2017. The patient agreed to undergo repeat surgical debulking. Upon review of the preoperative MRI, the cisternal component of the tumor had substantially decreased in size. Although uncommon, this reflects delayed, pseudoprogression which, in our case, was self-limiting. This raises a question regarding when to proceed with surgical intervention of growing VS following radiosurgery given the potential for delayed resolution of radiation necrosis and demonstrates a gap in our current literature involving surgery of VS following radiosurgery.

Surgery of the lateral skull base: a 50-year endeavour

Disregarding the widely used division of skull base into anterior and lateral, since the skull base should be conceived as a single anatomic structure, it was to our convenience to group all those approaches that run from the antero-lateral, pure lateral and postero-lateral side of the skull base as “Surgery of the lateral skull base”. “50 years of endeavour” points to the great effort which has been made over the last decades, when more and more difficult surgeries were performed by reducing morbidity. The principle of lateral skull base surgery, “remove skull base bone to approach the base itself and the adjacent sites of the endo-esocranium”, was then combined with function preservation and with tailoring surgery to the pathology. The concept that histology dictates the extent of resection, balancing the intrinsic morbidity of each approach was the object of the first section of the present report. The main surgical approaches were described in the second section and were conceived not as a step-by-step description of technique, but as the highlighthening of the surgical principles. The third section was centered on open issues related to the tumor and its treatment. The topic of vestibular schwannoma was investigated with the current debate on observation, hearing preservation surgery, hearing rehabilitation, radiotherapy and the recent efforts to detect biological markers able to predict tumor growth. Jugular foramen paragangliomas were treated in the frame of radical or partial surgery, radiotherapy, partial “tailored” surgery and observation. Surgery on meningioma was debated from the point of view of the neurosurgeon and of the otologist. Endolymphatic sac tumors and malignant tumors of the external auditory canal were also treated, as well as chordomas, chondrosarcomas and petrous bone cholesteatomas. Finally, the fourth section focused on free-choice topics which were assigned to aknowledged experts. The aim of this work was attempting to report the state of the art of the lateral skull base surgery after 50 years of hard work and, above all, to raise questions on those issues which still need an answer, as to allow progress in knowledge through sharing of various experiences. At the end of the reading, if more doubts remain rather than certainties, the aim of this work will probably be achieved.

Oculomotor Schwannomas: A Systematic Review and Report of Two Pediatric Cases Treated with Fractionated Cyberknife Stereotactic Radiotherapy

OBJECTIVE

Pediatric oculomotor nerve schwannomas are rare and challenging lesions due to the high morbidity associated with surgical intervention and their proximity to critical structures limiting the opportunity for stereotactic radiosurgery. We aim to report and review the novel use of fractionated Cyberknife (Accuray, Inc., Sunnyvale, California, USA) stereotactic radiotherapy in pediatric patients with oculomotor schwannomas.

METHODS

A systematic review of PubMed, Embase, and Cochrane was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Two patients, ages 8 and 10 years, with tumor volumes of 0.1 cm³ and 0.2 cm³, respectively, were treated with fractionated Cyberknife radiotherapy at our institution. A total dose of 45-50 Gy was administered over 25 fractions (1.8-2.0 Gy per fraction) to the 82%-84% isodose line. Serial magnetic resonance imaging was obtained for long-term follow-up (56-58 months).

RESULTS

We found 14 articles published between 1982 and 2018 that reported a total of 18 pediatric patients with intracranial oculomotor schwannomas. No previously described cases of pediatric intracranial oculomotor schwannomas were treated with radiation therapy. In both of our patients, radiographic tumor control was achieved at a mean follow-up of 57 months, with 1 patient displaying a decrease in tumor volume. Neither patient exhibited any worsening of their presenting symptoms, nor did either patient develop any new neurocognitive deficits following treatment.

CONCLUSIONS

Fractionated Cyberknife radiotherapy is an effective and well-tolerated treatment option for intracranial oculomotor nerve schwannomas with excellent tumor control rates, similar to surgical and radiosurgical techniques, while sparing critical surrounding structures.

Hearing Preservation for Vestibular Schwannomas Treated with Stereotactic Radiosurgery or Fractionated Stereotactic Radiotherapy

BACKGROUND

Vestibular schwannomas (VS) are benign intracranial neoplasms arising from the eighth cranial nerve for which targeted radiation therapy (RT) has proved increasingly successful. However, long-term hearing and related cranial nerve outcomes have been disputed for the 3 current RT modalities.

OBJECTIVE

To determine differences in hearing preservation for patients treated with stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (FSRT), or hypofractionated stereotactic radiotherapy (hypoFSRT) for VS.

METHODS

A retrospective electronic chart review was conducted for all patients with unilateral VS treated with primary RT at a single academic medical center between 2000 and 2017. The primary outcome measure was preservation of serviceable hearing status in the affected ear at last follow-up. Secondary outcomes included tinnitus, vertigo, and imbalance.

RESULTS

A total of 33 FSRT cases, 21 SRS cases, and 6 hypoFSRT cases were identified. Postoperative deterioration in serviceable hearing and tinnitus showed significant differences across cohorts. The SRS cohort had a higher baseline incidence of nonserviceable hearing and disequilibrium compared with other cohorts before RT (P = 0.001 and 0.022, respectively); no differences in baseline morbidity were observed for vertigo and tinnitus. The 5-year tumor control rate was 95.2%, 93.9%, and 100% with SRS, FSRT, and hypoFSRT, respectively.

CONCLUSIONS

Our series indicated an excellent tumor control rate in all the modalities. Our SRS cohort showed increased incidence and shorter time to hearing deterioration compared with the FSRT and hypoFSRT cohorts. The FSRT and hypoFSRT cohorts have shown comparable overall outcomes. Onset of post-RT tinnitus was observed only with FSRT.

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.

Risk Recall of Complications Associated with Vestibular Schwannoma Treatment

OBJECTIVE

To assess the risk recall of complications among patients who underwent different vestibular schwannoma (VS) treatments.

STUDY DESIGN

Patients with VS completed a voluntary and anonymous survey.

SETTING

Survey links were distributed via the Acoustic Neuroma Association (ANA) website, Facebook, and email list.

SUBJECTS AND METHODS

Surveys were distributed to ANA members from January to March 2017. Of the 3200 ANA members with a VS diagnosis at the time of survey distribution, 789 (25%) completed the survey.

RESULTS

Subjects reported the following incidence of posttreatment complications: imbalance (60%), hearing issues (51%), dry eyes (30%), headache (29%), and facial weakness (27%). Overall, 188 (25%) recalled remembering all the risks associated with their treatment. Among those in the surgical cohort (52%) who experienced balance issues, facial weakness, cerebrospinal fluid leak, meningitis, and stroke, 73%, 91%, 77%, 67%, and 33% claimed recall of these associated risks. Among those in the radiosurgery cohort (28%) who experienced balance issues, facial weakness, and hydrocephalus, 56%, 52%, and 60% recalled discussions of those risks. Patients with higher-level education (P = .026) and those who underwent surgery (P = .001) had a significantly higher risk recall ratio, while sex, age, and tumor size were not significant contributing factors.

CONCLUSION

Not all patients with VS who experienced treatment complications recalled remembering those risks being discussed with them. Patients with higher education and those who underwent surgery had a better recall of risks associated with different treatment modalities. The risk recall ratio of patients experiencing complications ranged 33% to 91%, suggesting an opportunity for decision-making and discussion improvement.

Effect of Gamma Knife Radiosurgery on Vestibular Schwannoma with Serviceable Hearing: A Single-Center Indian Study

OBJECTIVE

Gamma Knife radiosurgery (GKRS) is an established treatment modality for vestibular schwannomas (VSs). The tumor control and hearing preservation rates suggest that GKRS is a good alternative treatment for small- and medium-size VS. Data are lacking from India regarding GKRS for VSs. Our aim was to find the hearing preservation and tumor control rates and the factors contributing to these.

METHODS

In a retrospective 9-year study period, 87 patients had undergone GKRS for unilateral VS with Gardner-Robertson (GR) class I or II serviceable hearing. All 87 had been evaluated with magnetic resonance imaging and audiometry before GKRS and during follow-up to assess for the factors influencing tumor control and hearing preservation.

RESULTS

Of the 87 patients, 77 with a minimum follow-up of 2 years and magnetic resonance imaging and audiometry evaluations available were included in the present study. The median follow-up period was 30 months. The tumor control rate and hearing preservation rate was 96.1% and 79.2%, respectively. Hearing preservation was not affected by the tumor volume. However, age >40 years, pre-GKRS pure tone average <30 decibels, speech discrimination score >85%, pre-GKRS Gardner-Robertson grade I hearing, mean cochlear dose <4 Gy, and pre-GKRS Ohata class of laterality C, D, E were significant on univariate analysis. The multivariate analysis revealed that age >40 years (P = 0.017), pre-GKRS pure tone average <30 decibels (P = 0.002), and Gardner-Robertson class I (P = 0.001) were significant factors. No patient developed cranial nerve dysfunction, hydrocephalus, or malignant degeneration.

CONCLUSION

For most patients with small VSs, GKRS will be an effective alternative treatment to microsurgery with retained serviceable hearing and good tumor control.

LINAC radiosurgery treatment for vestibular schwannoma

OBJECTIVE

The aims of our study were to evaluate tumour response in a series of patients with vestibular schwannoma (VS) treated with linear accelerator stereotactic radiosurgery (LINAC-RS), to describe the complications and to analyze the variables associated with the response to treatment.

MATERIAL AND METHODS

This retrospective descriptive study included 64 patients treated from 2010 to 2016 with a minimum follow-up of one year, excluding patients with neurofibromatosis. Clinical-radiological parameters were evaluated. The treatment was performed using LINAC-RS. The prescribed dose was 12Gy at 90% isodose.

RESULTS

The mean age at treatment was 53 years, 56% were women. Ninety-eight percent of the patients had hearing loss, 71% with grade III according to the Gardner-Robertson Classification. The mean volume at treatment was 2.92cc and the mean follow-up, 40.95 months. The overall therapeutic success was 90%, reaching 100% at 12 and 24 months, and 86% after 36 months of follow-up. The radiological result was significantly related to the initial tumour volume (p<0.037). In 20 patients there was evidence of transient tumour growth compatible with pseudoprogression. Acute complications were present in 37.5%, and transitory complications in 50%. Chronic complications were found in 20%, with 84% being permanent. The rate of acute complications was lower in patients with regression (p<0.016). Chronic complications were more frequent in the 41-60 year old age group (p<0.040).

CONCLUSIONS

In our study, the overall tumour control was in accordance with other published series. The radiological result significantly related to the tumour volume at the commencement of treatment. The rate of acute complications was lower in patients with regression.

Feasibility of MR-only radiation planning for hypofractionated stereotactic radiotherapy of schwannomas using non-coplanar volumetric modulated arc therapy

PURPOSE

To compare the dose calculation accuracy of plans done on a CT density-assigned MR image set for hypofractionated stereotactic radiotherapy (HSRT) using volumetric modulated radiation therapy containing non-coplanar beams.

METHODS

Eighteen patients diagnosed with schwannoma treated with HSRT were selected retrospectively. These patients underwent planning CT (pCT) for radiation therapy (RT) and contrast-enhanced three-dimensional fast-spoiled gradient-echo image (3D FSPGR) to assist tumor delineation. CT_plan is plan done on pCT. The structures body, bone, and air are contoured exclusively on MR image and assigned Hounsfield units of 25, + 1000, and - 1000, respectively. This is termed as MRCT. After registration, original plans from pCT are pasted on the MRCT. Dose calculation is done in two ways: (1) with preset MU values (DDC) and (2) with optimization (OPT_DC). Conformity indices and D_max and D_0.5cc of brainstem, gamma agreement index and correlation coefficient are analyzed. ANOVA test is carried out to find the significance of difference between plans.

RESULTS

The mean deviations of D_max and D_0.5cc of brainstem for CT_plan versus DDC are 2.49% and 1.45% respectively. The mean deviations of D_max and D_0.5cc of brainstem for CT_plan versus OPT_DC are - 1.56% and - 1.97%, respectively. Mean deviations of conformity index for DDC and OPT_DC are 0.84% and 0.89%, respectively. No significant difference was found with ANOVA test.

CONCLUSION

Results show that there is no difference between plans generated with actual CT data and MRCT data. Thus MR scans could be employed for radiation planning provided the verification image is available. This gives us confidence to reduce treatment margins where image registration process is avoided.

Long-term hearing outcomes after gamma knife surgery in patients with vestibular schwannoma with hearing preservation: evaluation in 92 patients with serial audiograms

The treatment strategy for patients with vestibular schwannoma (VS) is controversial, and data concerning the long-term hearing outcomes > 5 years after gamma knife surgery (GKS) are limited. The long-term hearing outcomes after GKS were evaluated in VS patients with hearing preservation. Ninety-two VS patients with a pure tone average (PTA) ≤ 50 dB were evaluated. The median age was 54 years; the median tumor volume was 1.5 cm³. The tumors were treated with a median margin dose of 12 Gy and a median mean cochlear dose of 4.0 Gy. At the time of GKS, 65 patients retained a PTA of 0-30 dB, and 27 had a PTA of 31-50 dB. The median follow-up period was 106 months. At the final follow-up, 2 (2%) developed tumor progression. During the median audiogram follow-up of 83 months, the PTA was ≤ 30 dB in 22 patients (24%) and 31-50 dB in 27 patients (29%); 43 patients (47%) worsened to a PTA > 50 dB. Hearing preservation rates were 66, 57, and 44% at 3, 5, and 10 years, respectively. In multivariate analysis, the mean cochlear dose (P < 0.001) and pre-GKS PTA (P = 0.045) were significant for hearing preservation. GKS was an effective treatment option for VS patients with a PTA ≤ 50 dB. As a lower cochlear dose and better pre-GKS PTA contributed to long-term hearing preservation, prophylactic GKS before hearing deterioration or tumor growth would be a treatment of choice if patients provided informed consent.

Retreatment of vestibular schwannoma with Gamma Knife radiosurgery: clinical outcome, tumor control, and review of literature

OBJECTIVE Gamma Knife radiosurgery (GKRS) has become an accepted treatment for vestibular schwannoma, with a high rate of tumor control and good clinical outcome. In a small number of cases, additional treatment is needed. This retrospective study examines the clinical outcome, reproducibility of volumetric response patterns, and tumor control rate after administering a second GKRS to treat vestibular schwannomas. METHODS A total of 38 patients were included: 28 patients underwent a radiosurgical procedure as the initial treatment (Group 1), and 10 patients underwent microsurgical resection with adjuvant radiosurgery on the tumor remnant as the initial treatment (Group 2). The indication for a second GKRS treatment was growth observed on follow-up imaging. The median margin dose was 11.0 Gy for the first procedure and 11.5 Gy for the second procedure. Tumor control after retreatment was assessed through volumetric analysis. Clinical outcome was assessed through medical chart review. RESULTS Median tumor volume at retreatment was 3.6 cm³, with a median treatment interval of 49 months. All patients showed tumor control in a median follow-up period of 75 months after the second radiosurgical procedure. Volumetric tumor response after the second procedure did not correspond to response after the first procedure. After retreatment, persisting House-Brackmann Grade II facial nerve dysfunction was observed in 3 patients (7.9%), facial spasms in 5 patients (13%), and trigeminal nerve hypesthesia in 3 patients (7.9%). Hearing preservation was not evaluated because of the small number of patients with serviceable hearing at the second procedure. CONCLUSIONS Repeat GKRS after a failed first treatment appears to be an effective strategy in terms of tumor control. The volumetric response after a repeat procedure could not be predicted by the volumetric response observed after first treatment. This justifies considering repeat GKRS even for tumors that do not show any volumetric response and show continuous growth after first treatment. An increased risk of mild facial and trigeminal nerve dysfunction was observed after the second treatment compared with the first treatment.

Long-term Treatment Response and Patient Outcomes for Vestibular Schwannoma Patients Treated with Hypofractionated Stereotactic Radiotherapy

Purpose

The aim of this study is to evaluate long-term treatment outcome and toxicities among vestibular schwannoma (VS) patients treated with hypofractionated stereotactic radiotherapy (HSRT).

Methods

383 patients with unilateral VS treated with HSRT (25 Gy, five fractions) between 1995 and 2007 were retrospectively reviewed. Treatment failure was defined as requiring salvage microsurgery. Posttreatment new/progressive clinical symptoms or increases in baseline tumor volume (BTV) due to treatment effect or progression were noted. Symptom outcomes were reported as baseline and posttreatment ± improvement, respectively. Symptoms were grouped by cranial nerve (CN) VII or CNVIII. Audiometry was assessed baseline and posttreatment hearing. Patients were grouped as having greater than serviceable hearing [Gardner Robertson (GR) score 1–2] or less than non-serviceable hearing (GR score 3–5) by audiometry.

Results

Median follow-up was 72.0 months. Nine (2.3%) experienced treatment failure. At last follow-up, 74 (19.3%) had new/progressive symptoms and were categorized as radiologic non-responders, whereas 300 (78.3%) had no tumor progression and were grouped as radiologic responders. Average pretreatment BTV for treatment failures, radiologic non-responders, and radiologic responders was 2.11, 0.44, and 1.87 cm³, respectively. Pretreatment CNVII and CNVIII symptoms were present in 9.4 and 93.4% of patients, respectively. Eight (24%) with pre-HSRT CNVII and 37 (10%) with pre-HSRT CNVIII symptoms recovered CN function post-HSRT. Thirty-five (9%) and 36 (9.4%) experienced new CNVII and CNVIII deficit, respectively, after HSRT. Of these, 20 (57%) and 18 (50%) recovered CNVII and CNVIII function, respectively, after HSRT. Evaluable audiograms were available in 199 patients. At baseline and at last follow-up, 65.8 and 36.2% had serviceable hearing, respectively. Fifty-one percent had preservation of serviceable hearing at last follow-up.

Conclusion

Treatment of VS with HSRT is effective with treatment success in 97.7% and an acceptable toxicity profile. Less than one-third of patients experience any new CNVII or CNVIII deficit posttreatment. Greater than 50% of patients with serviceable hearing at baseline maintained hearing function. Improved methods to differentiate treatment effect and tumor progression are needed.

Prognostic Indices for Predicting Facial Nerve Outcome following the Resection of Large Acoustic Neuromas

This study analyzes the simple ratio of anterior-to-posterior extension of large (>2.5 cm) acoustic neuromas relative to the internal auditory canal (ICA; anterior-posterior [A/P] index) as a tool for predicting risk of facial nerve (FN) injury. In total, 105 patients who underwent microsurgical resection for large acoustic neuromas were analyzed retrospectively. House-Brackmann (HB) scores were assessed immediately postoperatively, at 1 month, and at 1 year. Lateral-medial, inferior-superior, A/P, and maximum diameters were measured from preoperative magnetic resonance images. These measurements and the A/P index were analyzed using univariable and multivariable statistical models to assess relationship to FN outcomes. The retrosigmoid, translabyrinthine, and combined approaches were used, and the extent of resection was evaluated. For every 1 standard deviation increase in the A/P index, a patient was 3.87 times more likely have a higher postoperative HB score ( p  < 0.0001). Accordingly, for every 1-mm increase anterior to the IAC, a patient was 16% more likely have a higher postoperative HB score ( p  < 0.001). After controlling for tumor size, a patient was still 3.82 times more likely have a higher postoperative HB score for every 1 standard deviation increase in the A/P index ( p  < 0.0001). While larger tumor size trended toward worse postoperative HB scores, it was not statistically significant. Our prognostic index may be useful to assess the risk of FN injury preoperatively for large acoustic neuromas, while also providing information about the tumor-nerve relationship.

CT- and MRI-based gross target volume comparison in vestibular schwannomas

AIM

This study represents an enumeration and comparison of gross target volumes (GTV) as delineated independently on contrast-enhanced computed tomography (CT) and T1 and T2 weighted magnetic resonance imaging (MRI) in vestibular schwannomas (VS).

BACKGROUND

Multiple imaging in radiotherapy improves target localization.

METHODS AND MATERIALS

42 patients of VS were considered for this prospective study with one patient showing bilateral tumor. The GTV was delineated separately on CT and MRI. Difference in volumes were estimated individually for all the 43 lesions and similarity was studied between CT and T1 and T2 weighted MRI.

RESULTS

The male to female ratio for VS was found to be 1:1.3. The tumor was right sided in 34.9% and left sided in 65.1%. Tumor volumes (TV) on CT image sets were ranging from 0.251 cc to 27.27 cc. The TV for CT, MRI T1 and T2 weighted were 5.15 ± 5.2 cc, 5.8 ± 6.23 cc, and 5.9 ± 6.13 cc, respectively. Compared to MRI, CT underestimated the volumes. The mean dice coefficient between CT versus T1 and CT versus T2 was estimated to be 68.85 ± 18.3 and 66.68 ± 20.3, respectively. The percentage of volume difference between CT and MRI (%VD: mean ± SD for T1; 28.84 ± 15.0, T2; 35.74 ± 16.3) and volume error (%VE: T1; 18.77 ± 10.1, T2; 23.17 ± 13.93) were found to be significant, taking the CT volumes as the baseline.

CONCLUSIONS

MRI with multiple sequences should be incorporated for tumor volume delineation and they provide a clear boundary between the tumor and normal tissue with critical structures nearby.