Gamma Knife Radiosurgery For Vestibular Schwannomas Research Articles

Significance of Dosimetric Parameters in Patients Undergoing Gamma Knife Radiosurgery for Vestibular Schwannoma.

Vestibular schwannoma (VS) is a benign, encapsulated, and slow-growing tumor of the myelin-forming cells of the 8th cranial nerve. Gamma Knife radiosurgery (GKRS) has become a widely accepted primary treatment modality for small- to medium-sized VSs. In the case of VS, highly conformal, precisely focused radiation is delivered to the acoustic tumor in a single session under the direct supervision of a radiosurgery teamAim:This study aims to determine the significance of Conformity Index and Gradient Index (GI) in patients undergoing GKRS for VS, retrospectively, and re-assess the plans.Materials and Methods:A dosimetric study of 112 patients of VS (both operated and nonoperated) treated on Gamma Knife Perfexion unit at our hospital, over a 3-year period, was carried out retrospectively. The patients’ mean age at the time of GKRS was 48 years and the mean dose to the tumor margin was 13 Gy. The conformality of the treatment plan was determined by Conformity Index. GI determines fall off dose outside the target.Results:The dosimetric parameters such as Conformity Index and GI were calculated using the dose-volume histograms and the volume analysis tools available in the Leksell Gamma Plan using TMR 10 algorithm. The mean Paddick Conformity Index was found to be around 0.80 ± 0.085 and the mean GI was 2.67 ± 0.22.Conclusions:The dosimetric parameters can be used to evaluate the dose coverage and conformity and dose fall off outside the target.

Pre-existing Vestibular Symptoms Are Associated With Acute Vestibular Symptoms After Gamma Knife Therapy for Vestibular Schwannoma.

To identify pretreatment variables associated with the development of acute vestibular symptoms after Gamma Knife (GK) treatment for Vestibular Schwannoma (VS). Retrospective case series. Tertiary neurotology referral center. Patients treated with GK radiosurgery for VS between March 2007 and March 2017 were considered for this study. Patients with neurofibromatosis type II, previous VS surgery, follow-up less than 6 months, or the lack of T2 magnetic resonance imaging (MRI) sequences from the day of treatment were excluded. The presence of acute vestibular symptoms arising within 6 months after GK was the main outcome variable. Tumor, patient, and treatment characteristics were gathered from the medical record. In total, 98 patients met inclusion criteria. The incidence of acute vestibular symptoms occurring within 6 months after GK treatment was 46.9%. Post-GK vestibular symptoms were reported at a significantly higher frequency among subjects who had reported vestibular symptoms before their treatment (p = 0.001). Tumor size was not associated with a propensity to develop acute vestibular symptoms (p = 0.397). The likelihood of receiving a referral to vestibular rehabilitation services was not significantly different among patients with larger versus smaller tumor size, as defined by 1.6 cm and 1.4 cm thresholds (p = 0.896, p = 0.654). Inquiries aimed at revealing a history of vestibular complaints may prove useful in counseling patients on the likelihood of experiencing acute vestibular symptoms after treatment of Vestibular Schwannoma with Gamma Knife therapy.

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

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. 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. 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 >40years (P= 0.017), pre-GKRS pure tone average <30decibels (P= 0.002), and Gardner-Robertson class I (P= 0.001) were significant factors. No patient developed cranial nerve dysfunction, hydrocephalus, or malignant degeneration. For most patients with small VSs, GKRS will be an effective alternative treatment to microsurgery with retained serviceable hearing and good tumor control.

Gamma Knife radiosurgery for treatment of growing vestibular schwannomas in patients with neurofibromatosis Type 2: a matched cohort study with sporadic vestibular schwannomas.

OBJECTIVE Neurofibromatosis Type 2 (NF2) is a tumor syndrome characterized by an autosomal dominant pattern of inheritance. The hallmark of NF2 is the development of bilateral vestibular schwannomas (VSs), generally by 30 years of age. One of the first-line treatment options for small to medium-large VSs is radiosurgery. Although radiosurgery shows excellent results in sporadic VS, its use in NF2-related VS is still a topic of dispute. The aim of this study was to evaluate long-term tumor control, hearing preservation rates, and factors influencing outcome of optimally dosed, contemporary Gamma Knife radiosurgery (GKRS) for growing VSs in patients with NF2 and compare the findings to data obtained in patients with sporadic VS also treated by means of GKRS. METHODS The authors performed a retrospective analysis of 47 growing VSs in 34 NF2 patients who underwent GKRS treatment performed with either the Model C or Perfexion Leksell Gamma Knife, with a median margin dose of 11 Gy. Actuarial tumor control rates were estimated using the Kaplan-Meier method. For patient- and treatment-related factors, a Cox proportional hazards model was used to identify predictors of outcome. Trigeminal, facial, and vestibulocochlear nerve function were assessed before and after treatment. NF2-related VS patients were matched 1:1 with sporadic VS patients who were treated in the same institute, and the same indications for treatment, definitions, and dosimetry were used in order to compare outcomes. RESULTS Actuarial tumor control rates in NF2 patients after 1, 3, 5, and 8 years were 98%, 89%, 87%, and 87%, respectively. Phenotype and tumor volume had significant hazard rates of 0.086 and 22.99, respectively, showing that Feiling-Gardner phenotype and a tumor volume not exceeding 6 cm3 both were associated with significantly better outcome. Actuarial rates of serviceable hearing preservation after 1, 3, 5, and 7 years were 95%, 82%, 59%, and 33%, respectively. None of the patients experienced worsening of trigeminal nerve function. Facial nerve function worsened in 1 patient (2.5%). No significant differences in tumor control, hearing preservation, or complications were found in comparing the results of GKRS for NF2-related VS versus GKRS for sporadic VS. CONCLUSIONS With modern GKRS, the use of low margin doses for treating growing VSs in patients with NF2 demonstrates good long-term tumor control rates. Feiling-Gardner phenotype and tumor volume smaller than 6 cm3 seem to be independently associated with prolonged progression-free survival, highlighting the clinical importance of phenotype assessment before GKRS treatment. In addition, no significant differences in tumor control rates or complications were found in the matched-control cohort analysis comparing GKRS for VS in patients with NF2 and GKRS for sporadic VS. These results show that GKRS is a valid treatment option for NF2-related VS, in addition to being a good option for sporadic VS, particularly in patients with the Feiling-Gardner phenotype and/or tumors that are small to medium in size. Larger tumors in patients with the Wishart phenotype appear to respond poorly to radiosurgery, and other treatment modalities should therefore be considered in such cases.

Gamma Knife Radiosurgery for Residual and Recurrent Vestibular Schwannomas After Previous Surgery: Clinical Results in a Series of 90 Patients and Review of the Literature

Complete removal of vestibular schwannomas (VS) is not always achievable without any risk of disabling postoperative complications, especially in terms of facial nerve function. Moreover, even after gross total removal, a relevant rate of recurrence has been reported. The aim of this study is to validate Gamma Knife radiosurgery (GKRS) as an effective strategy to treat tumor regrowth after previous surgery. Ninety patients treated with GKRS for VS after previous microsurgery were included in the present study. GKRS was performed at a median of 31 months (range, 4-174 months) postoperatively. Mean tumor volume was 3.35 cm3 (median, 2.5 cm3; range, 0.027-13 cm3) and median marginal dose was 13 Gy. At a mean follow-up of 77.2 months, tumor control was achieved in 90% of patients: 2 patients underwent repeated GKRS, and 7 patients underwent further microsurgery. Tumor shrinkage at last follow-up was recorded in 80.3% of cases. The complication rate was low and many consisted of a transient worsening of preexisting symptoms. The overall incidence of persisting facial nerve deficit and trigeminal nerve impairment was, in both cases, 3.3%. Two of 5 patients (40%) preserved functional hearing at last follow-up. One patient (1.1%) underwent ventriculoperitoneal shunting 12 months after GKRS. GKRS is a safe and effective treatment for growing residual and recurrent VSs, with tumor control obtained in 90% of cases and a low morbidity rate. Moreover, the possibility of treating patients with major medical comorbidities constitutes a significant advantage over repeated surgery.

Long-term outcome of gamma knife radiosurgery for vestibular schwannoma.

Objective We evaluated the long-term outcome of vestibular schwannoma (VS) treated with gamma knife radiosurgery (GKRS) as a primary treatment as well as an adjunct therapy. Materials and Methods We performed a retrospective review (2000-2012) of 82 patients with VS who received GKRS. Of 82 patients, 20 patients with prior resection received GKRS treatment as an adjunct therapy. The remainder of the patients (62) received GKRS as a primary treatment. Results GKRS for VS showed significant variations in tumor growth control (decreased in 44 patients [54%], arrested growth in 30 patients [36%], and increased tumor size in 8 patients [10%]). Progression-free survival rates after GKRS at 3, 5, and 10 years were 98%, 95%, and 95%, respectively. Hearing, facial nerve function, and Karnofsky performance scale were significantly improved after GKRS compared with pretreated status (79 versus 90). Two patients (2.5%) required resection again due to tumor progression and worsening of signs and symptoms. Conclusion Long-term follow-up demonstrated that GKRS offers a high rate of tumor control, preservation of multiple nerve functions, and a good quality of life in both new and recurrent patients with VS.

How to distinguish tumor growth from transient expansion of vestibular schwannomas following Gamma Knife radiosurgery

Typically, vestibular schwannomas (VS) react to Gamma Knife radiosurgery (GKRS) with a transient increase of tumor volume owed to tumor swelling at about 6 months followed by a reduction of tumor volume owed to tumor shrinkage at about 18 months. It is important to distinguish this transient tumor expansion (TTE) from tumor growth. We undertook this study to see if there is a typical time interval in the follow-up of VS following GKRS, which may indicate tumor growth rather than TTE. We retrospectively reviewed the patient charts of patients who underwent GKRS for unilateral sporadic VS at the Gamma Knife Center Zurich from 1994-2009 and who were treated by J. Siegfried or one of the authors (TM). Tumor progression was defined as an increase of tumor volume of ≥ 20 % as compared to the initial tumor volume at the earliest 2 years following GKRS. This time interval of ≥ 2 years was chosen in order to distinguish TTE from genuine tumor progression. Whenever tumor enlargement was suspected on follow-up MRI at ≥ 2 years following GKRS, tumor volumes were measured using custom software. From 1994-2009, 235 patients underwent GKRS in Zurich for unilateral sporadic VS. Tumor progression with a volume increase of ≥ 20 % occurred in 21/235 (8.9 %) patients at 3.4 ± 0.9 years following GKRS. Seventeen out of 235 (7 %) patients had a clinically relevant tumor progression requiring microsurgery or repeat radiosurgery. According to our data, time may be a good parameter distinguishing tumor progression due to tumor growth from TTE due to tumor swelling in VS following GKRS. Tumor growth seems to occur at about 3-4 years following GKRS for VS as opposed to TTE, which seems to be present at about 6-18 months following GKRS for VS.

Dose-Volume Effects on Hearing Preservation in Gamma-knife Radiosurgery of Vestibular Schwannomas

Dose-Volume Effects on Hearing Preservation in Gamma-knife Radiosurgery of Vestibular Schwannomas

Dosimetric and Clinical Analysis of Spatial Distribution of the Radiation Dose in Gamma Knife Radiosurgery for Vestibular Schwannoma

We investigated variations in the distribution of radiation dose inside (dose inhomogeneity) and outside (dose falloff) the target volume during Gamma Knife (GK) irradiation of vestibular schwannoma (VS). We analyzed the relationship between some parameters of dose distribution and the clinical and radiological outcome of patients. Data from dose plans of 203 patients treated for a vestibular schwannoma by GK C using same prescription dose (12 Gy at the 50% isodose) were collected. Four different dosimetric indexes were defined and calculated retrospectively in all plannings on the basis of dose-volume histograms: Paddick conformity index (PI), gradient index (GI), homogeneity index (HI), and unit isocenter (UI). The different measures related to distribution of the radiation dose were compared with hearing and tumor outcome of 203 patients with clinical and radiological follow-up of minimum 2 years. Mean, median, SD, and ranges of the four indexes of dose distribution analyzed were calculated; large variations were found between dose plans. We found a high correlation between the target volume and PI, GI, and UI. No significant association was found between the indexes of dose distribution calculated in this study and tumor control, tumor volume shrinkage, hearing worsening, loss of functional hearing, or complete hearing loss at last follow-up. Parameters of distribution of the radiation dose during GK radiosurgery for VS can be highly variable between dose plans. The tumor and hearing outcome of patients treated is not significantly related to these global indexes of dose distribution inside and around target volume. In GK radiosurgery for VS, the outcome seems more to be influenced by local radiation dose delivered to specific structures or volumes than by global dose gradients.

Tumor control and hearing preservation after Gamma Knife radiosurgery for vestibular schwannomas in neurofibromatosis type 2

To analyze the effect of Gamma Knife radiosurgery (GKS) on tumor control and hearing preservation rates in patients with vestibular schwannomas (VS) in a setting of neurofibromatosis type 2 (NF 2), a retrospective study was carried out at a tertiary-level referral Gamma Knife unit. Dose plans, pre- and postoperative radiology, and follow-up clinical records of patients with NF 2 who had undergone GKS for VS using a Leksell Gamma Knife (Elekta Instruments AB, Stockholm, Sweden) model B unit from 1997 to 2008 were reviewed. Thirty patients with 54 VS underwent GKS. The average age of the cohort was 29 years (range 10-56 years). Twenty-four patients had bilateral VS. The commonest clinical presentation was hearing loss and tinnitus. Primary GKS was given to 36 tumors, while 18 tumors received it as an adjunct to surgery. Average tumor size was 3.7 cc (range 0.1-13.3 cc). A median 12 Gy prescription dose (range 10-15 Gy) was administered at the 50% isodose (range 42-50%) to cover on average 91.5% of the tumor. Eighteen patients were available for clinical, 14 patients for radiological, and 5 patients (with useful hearing) for audiometric follow-up at an average of 26.6 months. The tumor control rate was 87.5% in this series (33.3% tumor regression), while hearing preservation was noted in 66.7% of cases. One patient developed worsening of facial function. GKS for VS provides satisfactory tumor control and hearing preservation in patients with NF 2. Long-term follow-up will determine future recommendations.

Quality of life after gamma knife radiosurgery treatment in patients with a vestibular schwannoma: the patient’s perspective

This study evaluates the impact of gamma knife radiosurgery (GKRS) on the quality of life (QOL) of patients with a sporadic vestibular schwannoma (VS). This study pertains to 108 VS patients who had GKRS in the years 2003 through 2007. Two different QOL questionnaires were used: medical outcome study short form 36 (SF36) and Glasgow benefit inventory (GBI). Radiosurgery was performed using a Leksell 4C gamma knife. The results of the QOL questionnaires in relation to prospectively and retrospectively gathered data of the VS patients treated by GKRS. Eventually, 97 patients could be included in the study. Their mean tumor size was 17 mm (range 6–39 mm); the mean maximum dose on the tumor was 19.9 Gy (range 16–25.5 Gy) and the mean marginal dose on the tumor was 11.1 (range 9.3–12.5 Gy). SF36 scores showed results comparable to those for a normal Dutch population. GBI showed a marginal decline in QOL. No correlation was found between QOL and gender, age, tumor size, or radiation dose. Increased audiovestibular symptoms after GKRS were correlated with a decreased GBI score, and decreased symptoms were correlated with a higher QOL post-GKRS. In this study shows that GKRS for VS has little impact on the general QOL of the VS patient. However, there is a wide range in individual QOL results. Individual QOL was influenced by the audiovestibular symptoms. No predictive patient, tumor, or treatment factors for QOL outcome after GKRS could be determined. Comparison with microsurgery is difficult because of intra group variability.

Microsurgery for vestibular schwannoma after gamma knife radiosurgery

We evaluated the clinical characteristics of microsurgery for vestibular schwannoma (VS) after failed gamma knife radiosurgery (GKS). Twelve patients, 5 men and 7 women aged 19 to 70 years (mean 54.5 years), who underwent microsurgery after failed GKS for VS were studied retrospectively. The median interval between GKS and microsurgery was 28.8 months (range, 6.6-120 months) and 4 patients had undergone previous microsurgery. The mean volume of tumour at GKS was 6.9 cm(3) (range, 0.5-19.7 cm(3)) and the mean prescription dose to the tumour margin was 12.3 Gy. Microsurgery involved the lateral suboccipital approach in all patients. Tumour expansion involved solid enlargement in 7 patients, cystic enlargement in 3, and central necrosis in 2. Bleeding was slight in all patients except in one, probably because of the previous irradiation. Adhesion to the brain stem was severe in 7 patients. Identification of the facial nerve was easy in 5 operations and difficult in 7. Dissection of the tumour from the facial nerve was difficult in most interventions because of severe adhesions or colour change. Severe adhesions between the trigeminal nerve and the tumour was observed in 2 patients. The tumour was subtotally removed except around the internal auditory canal in most patients. Only one residual tumour increased in size and needed second GKS. The function of the facial nerve deteriorated in 3 patients, was unchanged in 7, and improved in 2. All patients had lost hearing on the affected side at the time of microsurgery. Microsurgery for VS after failed GKS presents some technical difficulties. Dissection of the tumour from the facial nerve or brain stem is likely to be difficult. We recommend subtotal resection without dissection of the facial nerve and tumour, because growth of the residual tumour was rare in our series.