Gamma knife radiosurgery for acoustic tumors: multivariate analysis of four year results

Pentoxifylline and Vitamin E Can Restrict Radiation Necrosis via Vascular Pathways, Experimental Study in an Animal Model

OBJECTIVE

Radiation necrosis (RN) is a long-term side effect of Gamma Knife stereotactic radiosurgery that may require surgical intervention. Pentoxifylline and vitamin E have previously been shown to be effective in the treatment of RN in the published literature, but there are no data on the prophylactic use of these molecules or, more importantly, whether prophylaxis is required.

METHODS

The iatrogenic RN model included 50 Sprague-Dawley rats of both sexes. There were 7 treatment subgroups established. Gamma-Plan 8.32 was used to plan after magnetic resonance scans were performed in a specially designed frame. The injection doses used in the treatment groups were vitamin E (30 mg/kg/day in a single dose) and pentoxifylline (50 mg/kg/day in 2 doses). Control magnetic resonance scans were performed at the end of a 16-week treatment, and the subjects were decapitated for pathological evaluations.

RESULTS

The intensity of hypoxia - inducible factor 1α immunoreactivity is statistically significantly lower in the therapeutic vitamin E, prophylactic pentoxifylline and vitamin E, and therapeutic pentoxifylline and vitamin E groups than in the other groups. Similarly, the intensity of vascular endothelial growth factor immunoreactivity was reduced in the therapeutic vitamin E and prophylactic pentoxifylline and vitamin E treatment modality groups. When compared with other groups, the therapeutic pentoxifylline group had significantly fewer vascular endothelial growth factor-immunoreactive cells in the perinecrotic area, with an accompanying decreased contrast enhancement pattern.

CONCLUSIONS

Both vitamin E and pentoxifylline are effective for the treatment and/or restriction of RN, either alone or in combination. The use of these molecules as a preventive measure did not outperform the therapeutic treatment.

Long-Term Outcome of Unilateral Acoustic Neuromas With or Without Hearing Loss: Over 10 Years and Beyond After Gamma Knife Radiosurgery

BACKGROUND

Since the long-term outcomes of 162 patients who underwent gamma knife radiosurgery (GKS) as an initial or adjuvant treatment for acoustic neuromas (ANs) with unilateral hearing loss were first reported in 1998, there has been no report of a comprehensive analysis of what has changed in GKS practice.

METHODS

We performed a retrospective study of the long-term outcomes of 106 patients with unilateral sporadic ANs who underwent GKS as an initial treatment. The mean patient age was 50 years, and the mean initial tumor volume was 3.68 cm3 (range, 0.10-23.30 cm3). The median marginal tumor dose was 12.5 Gy (range, 8.0-15.0 Gy) and the median follow-up duration was 153 months (range, 120-216 months).

RESULTS

The tumor volume increased in 11 patients (10.4%), remained stationary in 27 (25.5%), and decreased in 68 patients (64.2%). The actuarial 3, 5, 10, and 15-year tumor control rates were 95.3 ± 2.1%, 94.3 ± 2.2%, 87.7 ± 3.2%, and 86.6 ± 3.3%, respectively. The 10-year actuarial tumor control rate was significantly lower in the patients with tumor volumes of ≥ 8 cm3 (P = 0.010). The rate of maintaining the same Gardner-Robertson scale grade was 28.6%, and that of serviceable hearing was 46.4%. The rates of newly developed facial and trigeminal neuropathy were 2.8% and 4.7%, respectively. The patients who received marginal doses of less than 12 Gy revealed higher tumor control failure rates (P = 0.129) and newly occurred facial or trigeminal neuropathy rates (P = 0.040 and 0.313, respectively).

CONCLUSION

GKS as an initial treatment for ANs could be helpful in terms of tumor control, the preservation of serviceable hearing, and the prevention of cranial neuropathy. It is recommended to perform GKS as soon as possible not only for tumor control in unilateral ANs with hearing loss but also for hearing preservation in those without hearing loss.

The 100 Most Highly Cited Publications on Hearing Preservation for Vestibular Schwannomas

OBJECTIVE

Vestibular schwannomas are benign, slow-growing tumors that often reduce patient quality of life by compressing nearby nerves. Neurological function preservation is one of the indicators of treatment success, with hearing preservation being the most difficult to obtain. This paper provides a bibliometric analysis of hearing preservation in treating acoustic neuromas and a greater understanding of the most highly cited articles, which have enhanced our understanding of this topic.

METHODS

Key terms of "acoustic neuroma," "vestibular schwannoma," and "hearing preservation" were queried through Web of Science. Articles were sorted by citation frequency, and the top 100 articles were recorded for title, name of first author, journal title, year of publication, total number of citations (and associated rank), average number of citations per year, country of the first author's associated institution, and type of study.

RESULTS

The top 100 cited articles were published from 1980 to 2014. The United States had the highest involvement as a country (55%), the University of Pittsburgh as an institution (13%), and The Journal of Neurosurgery as a publishing source (27%). Fourteen were reviews, and 86 were clinical papers. Of the 86, 73 were retrospective studies.

CONCLUSION

Bibliometric analyses summarize and assess potential areas of strength and knowledge gaps within the literature. Studies on hearing preservation in vestibular schwannomas mostly consist of retrospective reviews that assess postoperative outcomes of microsurgery and radiosurgery. Prospective studies and novel treatment options for hearing preservation in vestibular schwannomas are needed to increase current literature diversity.

Long-Term Hearing Outcomes From Gamma Knife Treatment for Vestibulocochlear Nerve Schwannomas in a Large, Tertiary Care, Academic Hospital

OBJECTIVE

Describe long-term hearing outcomes with audiologic data with modern stereotactic radiosurgery techniques for vestibular schwannoma tumors.

BACKGROUND

Since the mid-20th century, stereotactic radiosurgery has been an option for central nervous system tumors. Due to the non-invasive manner of treatment, this was extended to treatment for benign vestibular schwannomas without intracranial surgery. Modern advances have localized radiation and reduced dosage, but data are still lacking in the long-term hearing outcomes of this method of treatment. As one of the national leaders in this procedure, we present our full database of these outcomes over the full time period of our institutions utility of this modality.

METHODS

A retrospective review was performed of all patients undergoing stereotactic radiotherapy for vestibular schwannomas within the study period of 1998 to 2019 and their audiograms analyzed along with patient data. Laterality Gardner-Robertson hearing score changes were the primary outcome analyzed for each patient; and controls were placed to accommodate for patient demographic data.

RESULTS

Long-term, multi-year audiometric evaluation showed statistically significant loss of serviceable hearing and reduction in hearing ability with the use of stereotactic radiosurgery for treatment of vestibular schwannomas.

CONCLUSIONS

Little long-term data exists on the audiometric outcomes related to stereotactic radiosurgery treatment for vestibular schwannomas. Our institution has performed more than 300 stereotactic radiosurgery treatments showing a continued reduction over time in serviceable hearing. Practitioners should advise patients undergoing treatment for vestibular schwannomas with this treatment of long-term results.

Long-term outcomes of rotating gamma knife for vestibular schwannoma: A 4-year prospective longitudinal study of 89 consecutive patients in Vietnam

Background:

Microsurgical total removal of vestibular schwannoma (VS) is the definitive treatment but has a high incidence of postoperative neurological deficits. Rotating Gamma Knife (RGK) is a preferred option for a small tumor. This study aims to evaluate long-term neurological outcomes of RGK for VS.

Methods:

This prospective longitudinal study was conducted at the Nuclear Medicine and Oncology Center, Bach Mai Hospital, Hanoi, Vietnam. Eighty-nine consecutive patients were enrolled from October 2011 to October 2015 and followed up to June 2017. RGK was indicated for VS measuring <2.2 cm, while RGK for tumors measuring 2.2–3 cm was considered in patients with severe comorbidities, high-risk surgery, and who denied surgery. Concurrently, VS consisted of newly diagnosed, postoperative residual, and recurrent tumors. Patients with neurofibromatosis type 2 were excluded from the study. Primary outcomes were radiological tumor control rate, vestibulocochlear functions, facial and trigeminal nerve preservation. Stereotactic radiosurgery was performed by the Rotating Gamma System Gamma ART 6000.

Results:

The tumors were measured 20.7 ± 5.6 mm at pre treatment and 17.6 ± 4.1 mm at 3-year post treatment. The mean radiation dose was 13.5 ± 0.9 Gy. Mean follow-up was 40.6 ± 13.3 months. The radiological tumor control rate was achieved 95.5% at 5-year post treatment. The hearing and vestibular functions were preserved in 70.3% and 68.9%, respectively. The facial and trigeminal nerve preservation rates were 94.4% and 73.3%, respectively.

Conclusion:

RGK is an effective and safe treatment for VS measuring ≤3 cm with no significant complications during long-term follow-up.

Collagen Family Genes Associated with Risk of Recurrence after Radiation Therapy for Vestibular Schwannoma and Pan-Cancer Analysis

Background

The safety of radiotherapy techniques in the treatment of vestibular schwannoma (VS) shows a high rate of tumor control with few side effects. Neuropeptide Y (NPY) may have a potential relevance to the recurrence of VS. Further research is still needed on the key genes that determine the sensitivity of VS to radiation therapy.

Materials and Methods

Transcriptional microarray data and clinical information data from VS patients were downloaded from GSE141801, and vascular-related genes associated with recurrence after radiation therapy for VS were obtained by combining information from MSigDB. Logistics regression was applied to construct a column line graph prediction model for recurrence status after radiation therapy. Pan-cancer analysis was also performed to investigate the cooccurrence of these genes in tumorigenesis.

Results

We identified eight VS recurrence-related genes from the GSE141801 dataset. All of these genes were highly expressed in the VS recurrence samples. Four collagen family genes (COL5A1, COL3A1, COL4A1, and COL15A1) were further screened, and a model was constructed to predict the risk of recurrence of VS. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that these four collagen family genes play important roles in a variety of biological functions and cellular pathways. Pan-cancer analysis further revealed that the expression of these genes was significantly heterogeneous across immune phenotypes and significantly associated with immune infiltration. Finally, Neuropeptide Y (NPY) was found to be significantly and negatively correlated with the expression of COL5A1, COL3A1, and COL4A1.

Conclusions

Four collagen family genes have been identified as possible predictors of recurrence after radiation therapy for VS. Pan-cancer analysis reveals potential associations between the pathogenesis of VS and other tumorigenic factors. The relevance of NPY to VS was also revealed for the first time.

Tufts Medical Center Experience With Long-Term Follow-Up of Vestibular Schwannoma Treated With Gamma Knife Stereotactic Radiosurgery: Novel Finding of Delayed Pseudoprogression

Purpose

Our purpose was to evaluate the long-term outcomes of patients with vestibular schwannoma (VS) treated with Gamma Knife stereotactic radiosurgery (GKSRS) with modern techniques, with attention to posttreatment tumor growth dynamics, dosimetric predictors, and late toxicities.

Methods and Materials

One hundred twelve patients with VS were treated with GKSRS with a median dose of 12.5 Gy to the 50% isodose line treated between 2004 and 2015, with patients followed up to 15 years. Target and organ-at-risk doses were recorded, and tumor diameter/volume, audiologic decline, and trigeminal/facial nerve preservation were tracked from treatment onward.

Results

GKSRS yielded local control of 5, 10, and 15 years at 96.9%, 90.0%, and 87.1% respectively. Pseudoprogression was found in 45%, with a novel pattern detected with peak swelling at 31 months. Pseudoprogression was associated with smaller tumor diameter at treatment and fewer treatment isocenters, but not with the development of any toxicity, nor was it predicted by any dosimetric factor. Median time to hearing loss was 3.4 years with actuarial hearing preservation at 2, 5, and 10 years of 66.5%, 43.1%, and 37.6%, with rate of hearing loss correlating with maximum cochlea and modiolus doses. Trigeminal and facial nerve preservation rates were 92.7% and 97.6%, respectively. Increasing maximum tumor dose was associated with facial paresthesia.

Conclusions

Modern GKSRS is a safe and effective treatment for VS on long-term follow-up, with high levels of facial and trigeminal nerve preservation. A novel pattern of pseudoprogression has been identified suggesting longer imaging follow-up may be needed before initiating salvage in those without symptomatic progression. Several tumor and dosimetric predictors have been suggested for the development of different toxicities, requiring further evaluation.

Treatment Outcomes and Dose Rate Effects Following Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannomas

BACKGROUND

Gamma Knife radiosurgery (GKRS; Elekta AB) remains a well-established treatment modality for vestibular schwannomas. Despite highly effective tumor control, further research is needed toward optimizing long-term functional outcomes. Whereas dose-rate effects may impact post-treatment toxicities given tissue dose-response relationships, potential effects remain largely unexplored.

OBJECTIVE

To evaluate treatment outcomes and potential dose-rate effects following definitive GKRS for vestibular schwannomas.

METHODS

We retrospectively reviewed 419 patients treated at our institution between 1998 and 2015, characterizing baseline demographics, pretreatment symptoms, and GKRS parameters. The cohort was divided into 2 dose-rate groups based on the median value (2.675 Gy/min). Outcomes included clinical tumor control, radiographic progression-free survival, serviceable hearing preservation, hearing loss, and facial nerve dysfunction (FND). Prognostic factors were assessed using Cox regression.

RESULTS

The study cohort included 227 patients with available follow-up. Following GKRS 2-yr and 4-yr clinical tumor control rates were 98% (95% CI: 95.6%-100%) and 96% (95% CI: 91.4%-99.6%), respectively. Among 177 patients with available radiographic follow-up, 2-yr and 4-yr radiographic progression-free survival rates were 97% (95% CI: 94.0%-100.0%) and 88% (95% CI: 81.2%-95.0%). The serviceable hearing preservation rate was 72.2% among patients with baseline Gardner-Robertson class I/II hearing and post-treatment audiological evaluations. Most patients experienced effective relief from prior headaches (94.7%), tinnitus (83.7%), balance issues (62.7%), FND (90.0%), and trigeminal nerve dysfunction (79.2%), but not hearing loss (1.0%). Whereas GKRS provided effective tumor control independently of dose rate, GKRS patients exposed to lower dose rates experienced significantly better freedom from post-treatment hearing loss and FND (P = .044).

CONCLUSION

Whereas GKRS provides excellent tumor control and effective symptomatic relief for vestibular schwannomas, dose-rate effects may impact post-treatment functional outcomes. Further research remains warranted.

Systematic Review of Hearing Preservation After Radiotherapy for Vestibular Schwannoma

OBJECTIVE

To determine the long-term hearing preservation rate for spontaneous vestibular schwannoma treated by primary radiotherapy.

DATA SOURCES

The MEDLINE/PubMed, Web of Science, Cochrane Reviews, and EMBASE databases were searched using a comprehensive Boolean keyword search developed in conjunction with a scientific librarian. English language papers published from 2000 to 2016 were evaluated.

STUDY SELECTION

Inclusion criteria: full articles, pretreatment and posttreatment audiograms or audiogram based scoring system, vestibular schwannoma only tumor type, reported time to follow-up, published after 1999, use of either Gamma Knife or linear accelerator radiotherapy.

EXCLUSION CRITERIA

case report or series with fewer than five cases, inadequate audiometric data, inadequate time to follow-up, neurofibromatosis type 2 exceeding 10% of study population, previous treatment exceeding 10% of study population, repeat datasets, use of proton beam therapy, and non-English language.

DATA EXTRACTION

Two reviewers independently analyzed papers for inclusion. Class A/B, 1/2 hearing was defined as either pure tone average less than or equal to 50 db with speech discrimination score more than or equal to 50%, American Academy of Otolaryngology-Head & Neck Surgery (AAO-HNS) Hearing Class A or B, or Gardner-Robertson Grade I or II. Aggregate data were used when individual data were not specified.

DATA SYNTHESIS

Means were compared with student t test.

CONCLUSIONS

Forty seven articles containing a total of 2,195 patients with preserved Class A/B, 1/2 hearing were identified for analysis. The aggregate crude hearing preservation rate was 58% at an average reporting time of 46.6 months after radiotherapy treatment. Analysis of time-based reporting shows a clear trend of decreased hearing preservation extending to 10-year follow-up. This data encourages a future long-term controlled trial.

Longitudinal Radiographic Outcomes of Vestibular Schwannoma in Single and Fractionated Stereotactic Radiosurgery: A Retrospective Cohort Study

Management of vestibular schwannoma (VS) includes stereotactic radiosurgery (SRS) in single or fractionated treatments. There is a paucity of literature on the three-dimensional (3D) volumetric kinetics and radiological changes following SRS and no consensus on appropriate post-SRS surveillance imaging timeline. This is a retrospective cohort study with institutional review board approval. A total of 55 patients met study criteria. We collected volumetric kinetic data in VS treated with SRS over time using a target volume contouring software. We also tracked radiographic phenomena such as pseudoprogression and necrosis. A secondary objective was to describe our overall treatment success rate and any failures. For all treatments groups, pseudoprogression most typically occurred within 12 months post-SRS, after which tumor volumes on average normalized and then decreased from pretreatment size at the last follow-up. Only two patients required salvage therapy post-SRS and were considered SRS treatment failures. Both patients were in the five-fraction cohort but with a lower biologically equivalent dose. Our study is first to collect 3D volumetric kinetics of VS following single and fractionated SRS in contrast to extrapolations from single and two-dimensional measurements. Our longitudinal data also show initial increases in volume in the first 12 months post-SRS followed by later declines, setting up interesting questions regarding the utility of early posttreatment surveillance imaging in the asymptomatic patient. Finally, we show low rates of treatment failure (3.6%) and show in our cohort that SRS dose de-escalation posed a risk of treatment failure.

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.

Vestibular schwannomas: Accuracy of tumor volume estimated by ice cream cone formula using thin-sliced MR images

PURPOSE

We estimated the volume of vestibular schwannomas by an ice cream cone formula using thin-sliced magnetic resonance images (MRI) and compared the estimation accuracy among different estimating formulas and between different models.

METHODS

The study was approved by a local institutional review board. A total of 100 patients with vestibular schwannomas examined by MRI between January 2011 and November 2015 were enrolled retrospectively. Informed consent was waived. Volumes of vestibular schwannomas were estimated by cuboidal, ellipsoidal, and spherical formulas based on a one-component model, and cuboidal, ellipsoidal, Linskey's, and ice cream cone formulas based on a two-component model. The estimated volumes were compared to the volumes measured by planimetry. Intraobserver reproducibility and interobserver agreement was tested. Estimation error, including absolute percentage error (APE) and percentage error (PE), was calculated. Statistical analysis included intraclass correlation coefficient (ICC), linear regression analysis, one-way analysis of variance, and paired t-tests with P < 0.05 considered statistically significant.

RESULTS

Overall tumor size was 4.80 ± 6.8 mL (mean ±standard deviation). All ICCs were no less than 0.992, suggestive of high intraobserver reproducibility and high interobserver agreement. Cuboidal formulas significantly overestimated the tumor volume by a factor of 1.9 to 2.4 (P ≤ 0.001). The one-component ellipsoidal and spherical formulas overestimated the tumor volume with an APE of 20.3% and 29.2%, respectively. The two-component ice cream cone method, and ellipsoidal and Linskey's formulas significantly reduced the APE to 11.0%, 10.1%, and 12.5%, respectively (all P < 0.001).

CONCLUSION

The ice cream cone method and other two-component formulas including the ellipsoidal and Linskey's formulas allow for estimation of vestibular schwannoma volume more accurately than all one-component formulas.

A prediction model of radiation-induced necrosis for intracranial radiosurgery based on target volume

PURPOSE

This study aims to extend the observation that the 12 Gy-radiosurgical-volume (V12Gy) correlates with the incidence of radiation necrosis in patients with intracranial tumors treated with radiosurgery by using target volume to predict V12Gy. V12Gy based on the target volume was used to predict the radiation necrosis probability (P) directly. Also investigated was the reduction in radiation necrosis rates (ΔP) as a result of optimizing the prescription isodose lines for linac-based SRS.

METHODS

Twenty concentric spherical targets and 22 patients with brain tumors were retrospectively studied. For each case, a standard clinical plan and an optimized plan with prescription isodose lines based on gradient index were created. V12Gy were extracted from both plans to analyze the correlation between V12Gy and target volume. The necrosis probability P as a function of V12Gy was evaluated. To account for variation in prescription, the relation between V12Gy and prescription was also investigated.

RESULTS

A prediction model for radiation-induced necrosis was presented based on the retrospective study. The model directly relates the typical prescribed dose and the target volume to the radionecrosis probability; V12Gy increased linearly with the target volume (R²  > 0.99). The linear correlation was then integrated into a logistic model to predict P directly from the target volume. The change in V12Gy as a function of prescription was modeled using a single parameter, s (=-1.15). Relatively large ΔP was observed for target volumes between 7 and 28 cm³ with the maximum reduction (8-9%) occurring at approximately 18 cm³ .

CONCLUSIONS

Based on the model results, optimizing the prescription isodose line for target volumes between 7 and 28 cm³ results in a significant reduction in necrosis probability. V12Gy based on the target volume could provide clinicians a predictor of radiation necrosis at the contouring stage thus facilitating treatment decisions.

The Management and Imaging of Vestibular Schwannomas

Vestibular schwannomas are the most common cerebellopontine angle tumor. During the past century, the management goals of vestibular schwannomas have shifted from total resection to functional preservation. Current treatment options include surgical resection, stereotactic radiosurgery, and observation. Imaging has become a crucial part of the initial screening, evaluation, and follow-up assessment of vestibular schwannomas. Recognizing and understanding the management objectives, various treatment modalities, expected posttreatment findings, and complications allows the radiologist to play an essential role in a multidisciplinary team by providing key findings relevant to treatment planning and outcome assessment. The authors provide a comprehensive discussion of the surgical management, role of radiation therapy and observation, imaging differential, and pre- and posttreatment imaging findings of vestibular schwannomas.

Predictors of Trigeminal Neuropathy After Radiosurgery for Vestibular Schwannomas

PURPOSE

To analyze the relationship between dosimetric characteristics and symptoms related to trigeminal neuropathy (TN) observed after radiosurgery (RS) for vestibular schwannomas (VS); to propose guidelines to optimize planification in VS RS regarding TN preservation; and to detail the mechanism of TN impairment after VS RS.

METHODS AND MATERIALS

One hundred seventy-nine patients treated between 2011 and 2013 for VS RS and without trigeminal impairment before RS were included in a retrospective study. Univariate and multivariate analyses were performed to determine predictors of TN among characteristics of the patients, the dosimetry, and the VS.

RESULTS

There were 20 Koos grade 1, 99 grade 2, 57 grade 3, and 3 grade 4. Fourteen patients (7.8%) presented a transitory or permanent TN. Between the patients with and without TN after VS RS, there was no significant difference regarding dosimetry or VS volume itself. Significant differences (univariate analysis P<.05, Mann-Whitney test) were found for parameters related to the cisternal portion of the trigeminal nerve: total integrated dose, maximum dose, mean dose, volume of the Vth nerve (Volv), and volume of the Vth nerve receiving at least 11 Gy (VolVcist>11Gy), but also for maximal dose to the Vth nerve nucleus and intra-axial portion (Dose maxVax). After multivariate analysis, the best model predicting TN included VolVcist>11Gy (P=.0045), Dose maxVax (P=.0006), and Volv (P=.0058). The negative predictive value of this model was 97%.

CONCLUSIONS

The parameters VolVcist>11Gy, Dose maxVax, and Volv should be checked when designing dosimetry for VS RS.

Management of sporadic vestibular schwannoma

Vestibular schwannomas (VS) comprise 8% of all intracranial tumors and 90% of cerebellopontine angle and internal auditory canal neoplasms. Secondary to the widespread adoption of screening protocols for asymmetrical hearing loss and the increasing use of advanced imaging, the number of VS diagnosed each year continues to rise, while the average size has declined. Microsurgery remains the treatment of choice for large tumors, however the management of small- to medium-sized VS remains highly controversial with options including observation, radiotherapy, or microsurgery. Within this chapter, the authors provide an overview of the contemporary management of VS, reviewing important considerations and common controversies.

Postradiation imaging changes in the CNS: how can we differentiate between treatment effect and disease progression?

A familiar challenge for neuroradiologists and neuro-oncologists is differentiating between radiation treatment effect and disease progression in the CNS. Both entities are characterized by an increase in contrast enhancement on MRI and present with similar clinical signs and symptoms that may occur either in close temporal proximity to the treatment or later in the disease course. When radiation-related imaging changes or clinical deterioration are mistaken for disease progression, patients may be subject to unnecessary surgery and/or a change from otherwise effective therapy. Similarly, when disease progression is mistaken for treatment effect, a potentially ineffective therapy may be continued in the face of progressive disease. Here we describe the three types of radiation injury to the brain based on the time to development of signs and symptoms--acute, subacute and late--and then review specific imaging changes after intensity-modulated radiation therapy, stereotactic radiosurgery and brachytherapy. We provide an overview of these phenomena in the treatment of a wide range of malignant and benign CNS illnesses. Finally, we review the published data regarding imaging techniques under investigation to address this well-known problem.

Linac-based stereotactic radiosurgery and fractionated stereotactic radiotherapy for vestibular schwannomas: comparative observations of 139 patients treated at a single institution

Stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (SRT) have been recognized as an alternative to surgery for small to medium sized vestibular schwannoma (VS). This study analysed and compared the outcomes of VS treated with the first Thailand installation of a dedicated Linac-based stereotactic radiation machine using single-fraction radiosurgery (SRS), hypofraction stereotactic radiotherapy (HSRT) and conventional fraction stereotactic radiotherapy (CSRT). From 1997 to 2010, a total of 139 consecutive patients with 146 lesions of VS were treated with X-Knife at Ramathibodi hospital, Bangkok, Thailand. SRS was selected for 39 lesions (in patients with small tumors ≤3 cm and non-serviceable hearing function), whereas HSRT (79 lesions) and CSRT (28 lesions) were given for the remaining lesions that were not suitable for SRS. With a median follow-up time of 61 months (range, 12-143), the 5-year local control rate was 95, 100 and 95% in the SRS, HSRT and CSRT groups, respectively. Hearing preservation was observed after SRS in 75%, after HSRT in 87% and after CSRT in 63% of the patients. Cranial nerve complications were low in all groups. There were no statistically significant differences in local control, hearing preservation or complication between the treatment schedules. In view of our results, it may be preferable to use HSRT over CSRT for patients with serviceable hearing because of the shorter duration of treatment.

Changing times and early debates

The machine was soon being called the Gamma Knife. Its spread led to increasing numbers of papers from different centers but particularly Pittsburgh. As mentioned in the preface, the introduction of new methods in medicine is seldom without problems. There were a number of squabbles about the treatment of various indications. It was suggested that for AVMs, the GKS was unnecessary. For meningiomas, there was marked skepticism within the milieu itself in the early days. Metastases were not treated in Stockholm because of Leksell's opposition to the treatment of malignant disease, and indeed, these tumors became generally popular indications rather later. There was a thought that pituitary adenomas could be better treated with GKS but it proved too unreliable, and for these tumors, GKS remains an ancillary treatment method. The most marked disagreements were with respect of the vestibular schwannomas. This discussion continues to the present.

Long-term safety and efficacy of stereotactic radiosurgery for vestibular schwannomas: evaluation of 440 patients more than 10 years after treatment with Gamma Knife surgery

Object

Little is known about long-term outcomes, including tumor control and adverse radiation effects, in patients harboring vestibular schwannomas (VSs) treated with stereotactic radiosurgery > 10 years previously. The aim of this study was to confirm whether Gamma Knife surgery (GKS) for VSs continues to be safe and effective > 10 years after treatment.

Methods

A total of 440 patients with VS (including neurofibromatosis Type 2) treated with GKS between May 1991 and December 2000 were evaluable. Of these, 347 patients (79%) underwent GKS as an initial treatment and 93 (21%) had undergone prior resection. Three hundred fifty-eight patients (81%) had a solid tumor and 82 (19%) had a cystic tumor. The median tumor volume was 2.8 cm3 and the median marginal dose was 12.8 Gy.

Results

The median follow-up period was 12.5 years. The actuarial 5- and ≥ 10-year progression-free survival was 93% and 92%, respectively. No patient developed treatment failure > 10 years after treatment. According to multivariate analysis, significant factors related to worse progression-free survival included brainstem compression with a deviation of the fourth ventricle (p < 0.0001), marginal dose ≤ 13 Gy (p = 0.01), prior treatment (p = 0.02), and female sex (p = 0.02). Of 287 patients treated at a recent optimum dose of ≤ 13 Gy, 3 (1%) developed facial palsy, including 2 with transient palsy and 1 with persistent palsy after a second GKS, and 3 (1%) developed facial numbness, including 2 with transient and 1 with persistent facial numbness. The actuarial 10-year facial nerve preservation rate was 97% in the high marginal dose group (> 13 Gy) and 100% in the low marginal dose group (≤ 13 Gy). Ten patients (2.3%) developed delayed cyst formation. One patient alone developed malignant transformation, indicating an incidence of 0.3%.

Conclusions

In this study GKS was a safe and effective treatment for the majority of patients followed > 10 years after treatment. Special attention should be paid to cyst formation and malignant transformation as late adverse radiation effects, although they appeared to be rare. However, it is necessary to collect further long-term follow-up data before making conclusions about the long-term safety and efficacy of GKS, especially for young patients with VSs.

A comprehensive analysis of hearing preservation after radiosurgery for vestibular schwannoma

Object

Gamma Knife surgery (GKS) has evolved into a practical alternative to open microsurgical resection in the treatment of patients with vestibular schwannoma (VS). Hearing preservation rates in GKS series suggest very favorable outcomes without the possible acute morbidity associated with open microsurgery. To mitigate institutional and practitioner bias, the authors performed an analytical review of the published literature on the GKS treatment of vestibular schwannoma patients. Their aim was to objectively characterize the prognostic factors that contribute to hearing preservation after GKS, as well as methodically summarize the reported literature describing hearing preservation after GKS for VS.

Methods

A comprehensive search of the English-language literature revealed a total of 254 published studies reporting assessable and quantifiable outcome data obtained in patients who underwent radiosurgery for VSs. Inclusion criteria for articles were 4-fold: 1) hearing preservation rates reported specifically for VS; 2) hearing status reported using the American Association of Otolaryngology–Head and Neck Surgery (AAO-HNS) or Gardner-Robertson classification; 3) documentation of initial tumor size; and 4) GKS was the only radiosurgical modality in the treatment. In the analysis only patients with AAO-HNS Class A or B or Gardner-Robertson Grade I or II status at the last follow-up visit were defined as having preserved hearing. Hearing preservation and outcome data were then aggregated and analyzed based on the radiation dose, tumor volume, and patient age.

Results

The 45 articles that met the authors' inclusion criteria represented 4234 patients in whom an overall hearing preservation rate was 51%, irrespective of radiation dose, patient age, or tumor volume. Practitioners who delivered an average ≤ 13-Gy dose of radiation reported a higher hearing preservation rate (60.5% at ≤ 13 Gy vs 50.4% at > 13 Gy; p = 0.0005). Patients with smaller tumors (average tumor volume ≤ 1.5 cm3) had a hearing preservation rate (62%) comparable with patients harboring larger tumors (61%) (p = 0.8968). Age was not a significant prognostic factor for hearing preservation rates as in older patients there was a trend toward improved hearing preservation rates (56% at < 65 years vs 71% at ≥ 65 years of age; p < 0.1134). The average overall follow-up in the studies reviewed was 44.4 ± 32 months (median 35 months).

Conclusions

These data provide a methodical overview of the literature regarding hearing preservation with GKS for VS and a less biased assessment of outcomes than single-institution studies. This objective analysis provides insight into advising patients of hearing preservation rates for GKS treatment of VSs that have been reported, as aggregated in the published literature. Analysis of the data suggests that an overall hearing preservation rate of ~ 51% can be expected approaching 3–4 years after radiosurgical treatment, and the analysis reveals that patients treated with ≤ 13 Gy were more likely to have preserved hearing than patients receiving larger doses of radiation. Furthermore, larger tumors and older patients do not appear to be at any increased risk for hearing loss after GKS for VS than younger patients or patients with smaller tumors.

Radiation therapy and hearing loss

A review of literature on the development of sensorineural hearing loss after high-dose radiation therapy for head-and-neck tumors and stereotactic radiosurgery or fractionated stereotactic radiotherapy for the treatment of vestibular schwannoma is presented. Because of the small volume of the cochlea a dose-volume analysis is not feasible. Instead, the current literature on the effect of the mean dose received by the cochlea and other treatment- and patient-related factors on outcome are evaluated. Based on the data, a specific threshold dose to cochlea for sensorineural hearing loss cannot be determined; therefore, dose-prescription limits are suggested. A standard for evaluating radiation therapy-associated ototoxicity as well as a detailed approach for scoring toxicity is presented.

Hearing preservation and facial nerve function after microsurgery for intracanalicular vestibular schwannomas: comparison of middle fossa and retrosigmoid approaches

PURPOSE

Therapeutic options for vestibular schwannomas (VS) include microsurgery, stereotactic radiosurgery and conservative management. Early treatment of intracanalicular vestibular schwannomas (IVS) may be advisable because their spontaneous course will show hearing loss in most cases. Advanced microsurgical techniques and continuous intraoperative monitoring of cranial nerves may allow hearing preservation (HP) without facial nerve damage. However, there are still controversies about the definition of hearing preservation, and the best surgical approach that should be used.

METHODS

In this study, we reviewed the main data from the recent literature on IVS surgery and compared hearing, facial function and complication rates after the retrosigmoid (RS) and middle fossa (MF) approaches, respectively.

RESULTS

The results showed that the average HP rate after IVS surgery ranged from 58% (RS) to 62% (MF). HP varied widely depending on the audiometric criteria that were used for definition of serviceable hearing. There was a trend to show that the MF approach offered a better quality of postoperative hearing (not statistically significant), whereas the RS approach offered a better facial nerve preservation and fewer complications (not statistically significant).

CONCLUSIONS

We believe that the timing of treatment in the course of the disease and selection between radiosurgical versus microsurgical procedure are key issues in the management of IVS. Preservation of hearing and good facial nerve function in surgery for VS is a reasonable goal for many patients with intracanalicular tumors and serviceable hearing. Once open surgery has been decided, selection of the approach mainly depends on individual anatomical considerations and experience of the surgeon.

Optimal dose of stereotactic radiosurgery for acoustic neuromas: a systematic review

Radiosurgery is increasingly employed in the treatment of acoustic neuroma, but the optimal dose in terms of long-term tumour control and minimal adverse effects has not been established. We performed a systematic review of the published literature of radiosurgery of acoustic neuroma to assess whether the use of low dose radiosurgery is as effective as high dose treatment. Reports of radiosurgery for acoustic neuroma were identified through a Medline search. Studies with at least 15 patients and a median follow-up longer than 12 months were included. The relationship between actuarial 5-year progression-free survival (PFS), and tumour and treatment parameters was examined. Forty-two studies were included. Tumour control following lower radiosurgery doses was similar to that reported following high doses. Only 12 studies reported actuarial outcomes at 5 years. There was no relationship between PFS at 5 years and dose to the tumour margin. Radiosurgery of larger tumours was associated with lower 5 year PFS (p < 0.05). Although on initial inspection radiosurgery of acoustic neuroma with doses of 12 - 13 Gy seems to be as effective as higher dose treatment, the available reports are subject to a number of confounding factors, are not sufficiently statistically powered and there is only limited long-term actuarial outcome data. Currently, available studies do not provide sufficient confidence to support the claim that low dose radiosurgery is equally effective as higher doses in the long-term control of acoustic neuroma.

Current concepts in management of meningiomas and schwannomas

Meningiomas and schwannomas are the two most common extra-axial intracranial tumors in adults. Since their initial discovery, these often-benign lesions have shared a parallel metamorphosis in their management. The goal of this article is to provide a review of the current literature surrounding the mainstays of therapy for these lesions.

Hypofractionated CyberKnife stereotactic radiosurgery for acoustic neuromas with and without association to neurofibromatosis Type 2

CyberKnife stereotactic radiosurgery (CKSRS) has been proved effective in treating intra-cranial lesions. To treat acoustic neuroma (AN) patients with or without neurofibromatosis Type 2 (NF2) associations, the functional preservation of hearing, trigeminal nerve, and facial nerve are important. Twenty-one patients were treated with hypofractionated CKSRS. Fourteen non-NF2 and seven NF2 patients were enrolled. Cranial nerve function, audiograms, and magnetic resonance images (MRI) were monitored. Mean follow-up was 15 month. Tumors with volumes ranging from 0.13 to 24.8 cm3 (mean 5.4 cm3) were irradiated with the marginal dose 1800-2000 cGy/3 fractions. Tumors were treated with an 80 to 89% isodose line (mean 83%) and mean 97.9% tumor coverage. Two patients experienced hearing deterioration (16.7%) in the non-NF2 group, and 3 patients (50%) in the NF2 group. No facial or trigeminal dysfunction, brain stem toxicity, or cerebellar edema occurred. Tumor regression was seen in 9 patients (43%) and stable in 12 patients (57%). 100% tumor control rate was achieved. Hypofractionated CKSRS was not only effective in tumor control but also excellent in hearing preservation for non-NF2 AN. But for NF2 patients, although the tumor control was remarkable, hearing preservation was modest as in non-NF2 patients.

Effect of treatment plan quality on outcomes after radiosurgery for vestibular schwannoma

Object

The goal in this study was to review the effects of treatment plan quality on outcomes after radiosurgery for vestibular schwannoma (VS).

Methods

Between July 1988 and August 2005, 390 patients were treated. The results of this experience have been published recently. In this study the authors looked at dosimetry variables: conformity of treatment plan and steepness of dose gradient, in the same group of patients. Over the duration of this study, dosimetry evolved from a single isocenter with marginal conformity to multiple isocenters with high conformity. Multivariate statistics were used to determine the effects of these variables on tumor control and on two types of complication, facial weakness and facial numbness.

Results

The 5-year actuarial tumor control was 91%. Dosimetry had no effect on tumor control. Eighteen patients (4.6%) reported new-onset facial weakness and 14 (3.6%) reported new-onset facial numbness. Since 1994, when peripheral treatment doses were lowered to 1250 cGy, only three (1%) of 298 patients have experienced facial weakness and two (0.7%) of 298 have experienced facial numbness. Statistical analysis confirms, as in the prior study, that treatment volume and treatment dose are significant predictors of both facial weakness and facial numbness. In this model, prior tumor growth was also significant. Dosimetry, however, is definitely not a significant predictor of either complication.

Conclusions

Treatment dose appears to be much more important than treatment plan quality in the prevention of facial numbness or weakness after radiosurgery for VS.

Long-term Outcomes of Gamma Knife Stereotactic Radiosurgery of Vestibular Schwannomas

OBJECTIVE

Gamma Knife Stereotactic Radiosurgery (GK SRS) has become an important treatment modality for vestibular schwannomas. We evaluated the tumor control rate, patterns of tumor volume change and preservation of hearing following low-dose radiation for vestibular schwannomas in a homogeneous cohort group in which the mean marginal dose was 12 Gy.

METHODS

A total of 59 patients were enrolled in this study. All enrolled patients were followed-up for at least 5 years and the radiation dose was 11-13 Gy. Regular MRI, audiometry and clinical evaluations were done and tumor volumes were obtained from MRI using the OSIRIS program.

RESULTS

The tumor control rate was 97%. We were able to classify the patterns of change in tumor volume into three categories. Transient increases in tumor volume were detected in 29% of the patients and the maximum transient increase in tumor volume was identified at 6 to 30 months after GK SRS. The transient increases in tumor volume ranged from 121% to 188%. Hearing was preserved in 4 of the 12 patients who had serviceable hearing prior to treatment. There were no other complications associated with GK SRS.

CONCLUSION

Low-dose GK SRS was an effective and safe mode of treatment for vestibular schwannomas in comparison to the previously used high-dose GK SRS. Transient increases in tumor volume can be identified during the follow-up period after low-dose GK SRS for vestibular schwannomas. Physicians should be aware that these increases are not always indicative of treatment failure and that close observation is required following treatments. Unfortunately, a satisfactory hearing preservation rate was not achieved by reducing the radiation dose. It is thought that hearing preservation is a more sophisticated problem and further research is required.

Radiosurgery in patients with bilateral vestibular schwannomas

BACKGROUND

Patients with bilateral vestibular schwannomas offer a unique opportunity to determine the effectiveness of radiosurgery. By using the untreated tumor as an internal control, one can determine whether radiosurgery was able to interrupt the natural history of the treated tumor.

METHODS

From September 1998 to November 2004, 13 patients with neurofibromatosis type 2 had 14 tumors treated with radiosurgery at the University of Florida. A retrospective analysis was performed on these patients. Actuarial statistics were used to analyze local control in both the treated and untreated tumor.

RESULTS

The average follow-up length was 38 months. One patient failed to send a follow-up MRI. Actuarial local control in the treated tumors was 100% at 1 year and 92% at 2 and 5 years. Only 1 of the treated tumors continued to grow. In the untreated tumors, actuarial local control was 100% at 1 year, 78% at 2 years and 21% at 5 years. None of the untreated tumors decreased in size.

CONCLUSION

In all but 1 patient with follow-up data, radiosurgery successfully prevented or reversed tumor growth. Additionally, half of the untreated tumors continued to grow. This study shows that radiosurgery alters the natural history of vestibular schwannomas.

Treatment of vestibular schwannomas. Why, when and how?

Sporadic vestibular schwannoma (VS) causes unilateral hearing loss, tinnitus, vertigo and unsteadiness. In many cases, the tumour size may remain unchanged for many years following diagnosis, which is typically made by MRI. In the majority of cases the tumour is small, leaving the clinician and patient with the options of either serial scanning or active treatment by gamma knife radiosurgery (GKR) or microneurosurgery. Despite the vast number of published treatment reports, comparative studies are few, and evidence is no better than class III (May, 2006). The predominant clinical endpoints of VS treatment include tumour control, facial nerve function and hearing preservation. Less focus has been put on symptom relief and health-related quality of life (QOL). It is uncertain if treating a small tumour leaves the patient with a better chance of obtaining relief from future hearing loss, vertigo or tinnitus than by observing it without treatment. Recent data indicate that QOL is reduced in untreated VS patients, and may differ between patients who have been operated and patients treated with GKR. In the present paper we review the natural course and complaints of untreated VS patients, and the treatment alternatives and results. Furthermore, we review the literature concerning quality of life in patients with VS. Finally, we present our experience with a management strategy applied to more than 300 cases since 2001.

A review of 3 current radiosurgery systems

BACKGROUND

Stereotactic radiosurgery and fractionated stereotactic radiotherapy have become widespread techniques applied to the treatment of a variety of intracranial lesions. Rapid evolution of new technologies has now enabled clinicians to treat tumors outside the cranium and down the spinal axis. This review compares 3 commercially available systems in widespread use throughout the world.

METHODS

Literature review and interviews with practitioners in the United States were performed to establish data for a comparative analysis of the Gamma Knife (Elekta, Sweden), Novalis (BrainLabs, Germany), and CyberKnife systems (Accuray, Sunnyvale, CA). Cost analyses were deliberately excluded because of the need for detailed cost-benefit analysis beyond the scope of the review.

RESULTS

An unbiased comparative analysis was not possible because of the lack of objective data from a standard metric for these systems. Despite this shortcoming, disparate features of each system were compared and contrasted.

CONCLUSION

A careful assessment of each system, including its operational features, capabilities, and yearly capacity must be weighed against the composition of the radiosurgery team, the case mix of the practice, and the objectives of the clinical unit to yield the best fit.