scholarly journals Quantitative tumor volumetric responses after Gamma Knife radiosurgery for meningiomas

2016 ◽  
Vol 124 (1) ◽  
pp. 146-154 ◽  
Author(s):  
Gillian Harrison ◽  
Hideyuki Kano ◽  
L. Dade Lunsford ◽  
John C. Flickinger ◽  
Douglas Kondziolka
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Tumor Response ◽  
Gamma Knife Radiosurgery ◽  
Rate Of Change ◽  
Tumor Control ◽  
Volume Increase ◽  
Volume Response ◽  
Early Imaging

OBJECT The reported tumor control rates for meningiomas after stereotactic radiosurgery (SRS) are high; however, early imaging assessment of tumor volumes may not accurately predict the eventual tumor response. The objective in this study was to quantitatively evaluate the volumetric responses of meningiomas after SRS and to determine whether early volume responses are predictive of longer-term tumor control. METHODS The authors performed a retrospective review of 252 patients (median age 56 years, range 14–87 years) who underwent Gamma Knife radiosurgery between 2002 and 2010. All patients had evaluable pre- and postoperative T1-weighted contrast-enhanced MRIs. The median baseline tumor volume was 3.5 cm3 (range 0.2–33.8 cm3) and the median follow-up was 19.5 months (range 0.1–104.6 months). Follow-up tumor volumes were compared with baseline volumes. Tumor volume percent change and the tumor volume rate of change were compared at 3-month intervals. Eventual tumor responses were classified as progressed for > 15% volume change, regressed for ≤ 15% change, and stable for ± 15% of baseline volume at time of last follow-up. Volumetric data were compared with the final tumor status by using univariable and multivariable logistic regression. RESULTS Tumor volume regression (median decrease of −40.2%) was demonstrated in 168 (67%) patients, tumor stabilization (median change of −2.7%) in 67 (26%) patients, and delayed tumor progression (median increase of 104%) in 17 (7%) patients (p < 0.001). Tumors that eventually regressed had an average volume reduction of −18.2% at 3 months. Tumors that eventually progressed all demonstrated volume increase by 6 months. Transient progression was observed in 15 tumors before eventual decrease, and transient regression was noted in 6 tumors before eventual volume increase. CONCLUSIONS The volume response of meningiomas after SRS is dynamic, and early imaging estimations of the tumor volume may not correlate with the final tumor response. However, tumors that ultimately regressed tended to respond in the first 3 months, whereas tumors that ultimately progressed showed progression within 6 months.

scholarly journals Gamma Knife radiosurgery for vestibular schwannomas: evaluation of tumor control and its predictors in a large patient cohort in The Netherlands

2016 ◽  
Vol 124 (6) ◽  
pp. 1619-1626 ◽  
Author(s):  
Stijn Klijn ◽  
Jeroen B. Verheul ◽  
Guus N. Beute ◽  
Sieger Leenstra ◽  
Jef J. S. Mulder ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Hearing Preservation ◽  
Cox Proportional Hazards Model ◽  
Tumor Control ◽  
Complication Rates ◽  
Tumor Control Rate ◽  
Large Patient

OBJECT The authors of this study sought to assess tumor control and complication rates in a large cohort of patients who underwent Gamma Knife radiosurgery (GKRS) for vestibular schwannoma (VS) and to identify predictors of tumor control. METHODS The records of 420 patients treated with GKRS for VS with a median marginal dose of 11 Gy were retrospectively analyzed. Patients with neurofibromatosis Type 2 or who had undergone treatment for VS previously were excluded. The authors assessed tumor control and complication rates with chart review and used the Cox proportional hazards model to identify predictors of tumor control. Preservation of serviceable hearing, defined as Gardner-Robertson Class I–II, was evaluated in a subgroup of 71 patients with serviceable hearing at baseline and with available follow-up audiograms. RESULTS The median VS tumor volume was 1.4 cm3, and the median length of follow-up was 5.1 years. Actuarial 5-and 10-year tumor control rates were 91.3% and 84.8%, respectively. Only tumor volume was a statistically significant predictor of tumor control rate. The tumor control rate decreased from 94.1% for tumors smaller than 0.5 cm3 to 80.7% for tumors larger than 6 cm3. Thirteen patients (3.1%) had new or increased permanent trigeminal nerve neuropathy, 4 (1.0%) had new or increased permanent facial weakness, and 5 (1.2%) exhibited new or increased hydrocephalus requiring a shunting procedure. Actuarial 3-year and 5-year hearing preservation rates were 65% and 42%, respectively. CONCLUSIONS The 5-year actuarial tumor control rate of 91.3% in this cohort of patients with VS compared slightly unfavorably with the rates reported in other large studies, but the complication and hearing preservation rates in this study were similar to those reported previously. Various factors may contribute to the observed differences in reported outcomes. These factors include variations in treatment indication and in the definition of treatment failure, as well as a lack of standardization of terminology and of evaluation of complications. Last, differences in dosimetric variables may also be an explanatory factor.

CYBERKNIFE RADIOSURGERY FOR TRIGEMINAL SCHWANNOMAS

Neurosurgery ◽  
2009 ◽  
Vol 64 (suppl_2) ◽  
pp. A14-A18 ◽  
Author(s):  
Gordon T. Sakamoto ◽  
D. John Borchers ◽  
Furen Xiao ◽  
Hee-Jin Yang ◽  
Steven D. Chang ◽  
...  
Keyword(s):  
Surgical Resection ◽  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Benign Tumors ◽  
Tumor Control ◽  
Modest Improvement ◽  
Facial Numbness ◽  
The Mean

Abstract OBJECTIVE Trigeminal schwannomas (TS) are benign tumors that are managed by surgical resection and/or stereotactic radiosurgery. Most radiosurgical series report results using the gamma knife. The CyberKnife (Accuray, Inc., Sunnyvale, CA) is a frameless, robotic stereotactic radiosurgical system. In this series, we report our experience using the CyberKnife in the treatment of TS. METHODS We retrospectively reviewed the medical records and diagnostic imaging in 13 consecutive patients with TS who were treated with the CyberKnife from 2003 to 2007. Seven patients had a previous surgical resection. The mean tumor volume was 6.3 mL (range, 0.39–19.98 mL), and the mean marginal dose was 18.5 Gy. Six of the tumors were treated in a single session. The mean clinical follow-up period was 21.8 months (range, 7–53 months). RESULTS In this series, the tumor control rate was 100%. The average reduction in tumor volume was 45% (range, 14–98%). A modest improvement in facial pain was noted in 4 of the 6 patients who presented with this symptom. One patient had improvement in facial numbness, and another had improvement in pretreatment headaches. One patient developed jaw weakness and facial dysesthesia, and another patient developed asymptomatic radiation necrosis. CONCLUSION Although the length of follow-up is limited, we report our initial experience with CyberKnife treatment of TS. Our results demonstrate tumor control rates and clinical outcomes that parallel those of previous reports using gamma knife radiosurgery; however, long-term follow-up studies are needed.

Gamma Knife Radiosurgery as a Primary Treatment for Nonfunctioning Pituitary Adenoma Invading the Cavernous Sinus

2020 ◽  
Vol 98 (6) ◽  
pp. 371-377
Author(s):  
Won Jae Lee ◽  
Kyung-Rae Cho ◽  
Jung-Won Choi ◽  
Doo-Sik Kong ◽  
Ho Jun Seol ◽  
...  
Keyword(s):  
Pituitary Adenoma ◽  
Gamma Knife ◽  
Cavernous Sinus ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Primary Treatment ◽  
Tumor Control ◽  
Nonfunctioning Pituitary Adenoma ◽  
Maximal Diameter

<b><i>Objectives:</i></b> Surgical resection of nonfunctioning pituitary adenoma (NFPA) invading the cavernous sinus (CS) remains a challenging and significant factor associated with incomplete resection. The residual tumor in CS is usually treated with adjuvant stereotactic radiosurgery (SRS), but there is little information concerning SRS as an initial treatment for CS-invading NFPA. In this study, we investigated the tumor control rate and clinical outcomes of the patients who received primary gamma knife radiosurgery (GKRS) for CS-invading NFPA. <b><i>Methods:</i></b> This was a single-institute retrospective analysis of 11 patients. CS invasion of tumor was categorized using the modified Knosp grading system. The median tumor volume and maximal diameter were 1.6 cm<sup>3</sup> (range 0.4–6.5) and 17.2 mm (range 11.6–23.3), respectively. The median clinical follow-up period was 48.5 months (range 16.4–177.8). The median prescription dose at tumor margin was 15 Gy (range 11–25) and median prescription isodose was 50% (range 45–50). The maximum radiation dose to optic chiasm and optic nerve were 7.2 Gy (range 3.4–9.2) and 7.5 Gy (range 4.5–11.5), respectively. <b><i>Results:</i></b> Tumor control was achieved in all patients. The median tumor volume and maximal diameter at last follow-up were 0.4 cm<sup>3</sup> (range 0.1–2.3) and 11.4 mm (range 4.7–19.5), respectively. The median volume reduction rate was 52% (range 33–88). Six patients showed downgrading of modified Knosp grade after GKRS. No patients developed GKRS-related complications such as hypopituitarism or visual disturbance. <b><i>Conclusions:</i></b> SRS may be an alternative primary treatment option for CS-invading NFPA if there is no urgent and absolute indication for surgery such as optic apparatus compression.

Gamma Knife radiosurgery for larger-volume vestibular schwannomas

2011 ◽  
Vol 114 (3) ◽  
pp. 801-807 ◽  
Author(s):  
Huai-che Yang ◽  
Hideyuki Kano ◽  
Nasir Raza Awan ◽  
L. Dade Lunsford ◽  
Ajay Niranjan ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Univariate Analysis ◽  
Gamma Knife Radiosurgery ◽  
Volume Reduction ◽  
Vestibular Schwannomas ◽  
Maximum Diameter ◽  
Tumor Control ◽  
Recent Experience

Object Stereotactic radiosurgery (SRS) is an important management option for patients with small- and medium-sized vestibular schwannomas. To assess the potential role of SRS in larger tumors, the authors reviewed their recent experience. Methods Between 1994 and 2008, 65 patients with vestibular schwannomas between 3 and 4 cm in one extracanalicular maximum diameter (median tumor volume 9 ml) underwent Gamma Knife surgery. Seventeen patients (26%) had previously undergone resection. Results The median follow-up duration was 36 months (range 1–146 months). At the first planned imaging follow-up at 6 months, 5 tumors (8%) were slightly expanded, 53 (82%) were stable in size, and 7 (11%) were smaller. Two patients (3%) underwent resection within 6 months due to progressive symptoms. Two years later, with 63 tumors overall after the 2 post-SRS resections, 16 tumors (25%) had a volume reduction of more than 50%, 22 (35%) tumors had a volume reduction of 10–50%, 18 (29%) were stable in volume (volume change < 10%), and 7 (11%) had larger volumes (5 of the 7 patients underwent resection and 1 of the 7 underwent repeat SRS). Eighteen (82%) of 22 patients with serviceable hearing before SRS still had serviceable hearing after SRS more than 2 years later. Three patients (5%) developed symptomatic hydrocephalus and underwent placement of a ventriculoperitoneal shunt. In 4 patients (6%) trigeminal sensory dysfunction developed, and in 1 patient (2%) mild facial weakness (House-Brackmann Grade II) developed after SRS. In univariate analysis, patients who had a previous resection (p = 0.010), those with a tumor volume exceeding 10 ml (p = 0.05), and those with Koos Grade 4 tumors (p = 0.02) had less likelihood of tumor control after SRS. Conclusions Although microsurgical resection remains the primary management choice in patients with low comorbidities, most vestibular schwannomas with a maximum diameter less than 4 cm and without significant mass effect can be managed satisfactorily with Gamma Knife radiosurgery.

Magnetic resonance imaging characteristics and the prediction of outcome of vestibular schwannomas following Gamma Knife radiosurgery

2017 ◽  
Vol 127 (6) ◽  
pp. 1384-1391 ◽  
Author(s):  
Chih-Chun Wu ◽  
Wan-Yuo Guo ◽  
Wen-Yuh Chung ◽  
Hisu-Mei Wu ◽  
Chung-Jung Lin ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Reduction Ratio ◽  
Volume Reduction ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Mri Features ◽  
Before And After

OBJECTIVEGamma Knife surgery (GKS) is a promising treatment modality for patients with vestibular schwannomas (VSs), but a small percentage of patients have persistent postradiosurgical tumor growth. The aim of this study was to determine the clinical and quantitative MRI features of VS as predictors of long-term tumor control after GKS.METHODSThe authors performed a retrospective study of all patients with VS treated with GKS using the Leksell Gamma Knife Unit between 2005 and 2013 at their institution. A total of 187 patients who had a minimum of 24 months of clinical and radiological assessment after radiosurgery were included in this study. Those who underwent a craniotomy with tumor removal before and after GKS were excluded. Study patients comprised 85 (45.5%) males and 102 (54.5%) females, with a median age of 52.2 years (range 20.4–82.3 years). Tumor volumes, enhancing patterns, and apparent diffusion coefficient (ADC) values were measured by region of interest (ROI) analysis of the whole tumor by serial MRI before and after GKS.RESULTSThe median follow-up period was 60.8 months (range 24–128.9 months), and the median treated tumor volume was 3.54 cm3 (0.1–16.2 cm3). At last follow-up, imaging studies indicated that 150 tumors (80.2%) showed decreased tumor volume, 20 (10.7%) had stabilized, and 17 (9.1%) continued to grow following radiosurgery. The postradiosurgical outcome was not significantly correlated with pretreatment volumes or postradiosurgical enhancing patterns. Tumors that showed regression within the initial 12 months following radiosurgery were more likely to have a larger volume reduction ratio at last follow-up than those that did not (volume reduction ratio 55% vs 23.6%, respectively; p < 0.001). Compared with solid VSs, cystic VSs were more likely to regress or stabilize in the initial postradiosurgical 6–12-month period and during extended follow-up. Cystic VSs exhibited a greater volume reduction ratio at last follow-up (cystic vs solid: 67.6% ± 24.1% vs 31.8% ± 51.9%; p < 0.001). The mean preradiosurgical maximum ADC (ADCmax) values of all VSs were significantly higher for those with tumor regression or stabilization at last follow-up compared with those with progression (2.391 vs 1.826 × 10−3 mm2/sec; p = 0.010).CONCLUSIONSLoss of central enhancement after radiosurgery was a common phenomenon, but it did not correlate with tumor volume outcome. Preradiosurgical MRI features including cystic components and ADCmax values can be helpful as predictors of treatment outcome.

scholarly journals Gamma Knife radiosurgery for large vestibular schwannomas greater than 3 cm in diameter

2018 ◽  
Vol 128 (5) ◽  
pp. 1380-1387 ◽  
Author(s):  
Cheng-Wei Huang ◽  
Hsien-Tang Tu ◽  
Chun-Yi Chuang ◽  
Cheng-Siu Chang ◽  
Hsi-Hsien Chou ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Pure Tone Audiometry ◽  
Volume Reduction ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Recent Experience ◽  
Single Dimension

OBJECTIVEStereotactic radiosurgery (SRS) is an important alternative management option for patients with small- and medium-sized vestibular schwannomas (VSs). Its use in the treatment of large tumors, however, is still being debated. The authors reviewed their recent experience to assess the potential role of SRS in larger-sized VSs.METHODSBetween 2000 and 2014, 35 patients with large VSs, defined as having both a single dimension > 3 cm and a volume > 10 cm3, underwent Gamma Knife radiosurgery (GKRS). Nine patients (25.7%) had previously undergone resection. The median total volume covered in this group of patients was 14.8 cm3 (range 10.3–24.5 cm3). The median tumor margin dose was 11 Gy (range 10–12 Gy).RESULTSThe median follow-up duration was 48 months (range 6–156 months). All 35 patients had regular MRI follow-up examinations. Twenty tumors (57.1%) had a volume reduction of greater than 50%, 5 (14.3%) had a volume reduction of 15%–50%, 5 (14.3%) were stable in size (volume change < 15%), and 5 (14.3%) had larger volumes (all of these lesions were eventually resected). Four patients (11.4%) underwent resection within 9 months to 6 years because of progressive symptoms. One patient (2.9%) had open surgery for new-onset intractable trigeminal neuralgia at 48 months after GKRS. Two patients (5.7%) who developed a symptomatic cyst underwent placement of a cystoperitoneal shunt. Eight (66%) of 12 patients with pre-GKRS trigeminal sensory dysfunction had hypoesthesia relief. One hemifacial spasm completely resolved 3 years after treatment. Seven patients with facial weakness experienced no deterioration after GKRS. Two of 3 patients with serviceable hearing before GKRS deteriorated while 1 patient retained the same level of hearing. Two patients improved from severe hearing loss to pure tone audiometry less than 50 dB.The authors found borderline statistical significance for post-GKRS tumor enlargement for later resection (p = 0.05, HR 9.97, CI 0.99–100.00). A tumor volume ≥ 15 cm3 was a significant factor predictive of GKRS failure (p = 0.005). No difference in outcome was observed based on indication for GKRS (p = 0.0761).CONCLUSIONSAlthough microsurgical resection remains the primary management choice in patients with VSs, most VSs that are defined as having both a single dimension > 3 cm and a volume > 10 cm3 and tolerable mass effect can be managed satisfactorily with GKRS. Tumor volume ≥ 15 cm3 is a significant factor predicting poor tumor control following GKRS.

scholarly journals Gamma Knife radiosurgery for vestibular schwannoma: clinical results at long-term follow-up in a series of 379 patients

2014 ◽  
Vol 121 (Suppl_2) ◽  
pp. 123-142 ◽  
Author(s):  
Nicola Boari ◽  
Michele Bailo ◽  
Filippo Gagliardi ◽  
Alberto Franzin ◽  
Marco Gemma ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Hearing Preservation ◽  
Class I ◽  
Medium Size ◽  
Tumor Control ◽  
Long Term Follow Up

ObjectSince the 1990s, Gamma Knife radiosurgery (GKRS) has become the first-line treatment option for small- to medium-size vestibular schwannomas (VSs), especially in patients without mass effect–related symptoms and with functional hearing. The aim of this study was to assess the safety and efficacy of GKRS, in terms of tumor control, hearing preservation, and complications, in a series of 379 consecutive patients treated for VS.MethodsOf 523 patients treated at the authors' institution for VS between 2001 and 2010, the authors included 379 who underwent GKRS as the primary treatment. These patients were not affected by Type 2 neurofibromatosis and had clinical follow-up of at least 36 months. Clinical follow-up (mean and median 75.7 and 69.5 months, respectively) was performed for all patients, whereas audiometric and quantitative radiological follow-up examinations were obtained for only 153 and 219 patients, respectively. The patients' ages ranged from 23 to 85 years (mean 59 years). The mean tumor volume was 1.94 ± 2.2 cm3 (median 1.2 cm3, range 0.013–14.3 cm3), and the median margin dose was 13 Gy (range 11–15 Gy). Parameters considered as determinants of the clinical outcome were long-term tumor control, hearing preservation, and complications. A statistical analysis was performed to correlate clinical outcomes with the radiological features of the tumor, dose-planning parameters, and patient characteristics.ResultsControl of the tumor with GKRS was achieved in 97.1% of the patients. In 82.7% of the patients, the tumor volume had decreased at the last follow-up, with a mean relative reduction of 34.1%. The rate of complications was very low, with most consisting of a transient worsening of preexisting symptoms. Patients who had vertigo, balance disorders, or facial or trigeminal impairment usually experienced a complete or at least significant symptom relief after treatment. However, no significant improvement was observed in patients previously reporting tinnitus. The overall rate of preservation of functional hearing at the long-term follow-up was 49%; in patients with hearing classified as Gardner-Robertson (GR) Class I, this value was 71% and reached 93% among cases of GR Class I hearing in patients younger than 55 years.ConclusionsGamma Knife radiosurgery is a safe and effective treatment for VS, achieving tumor control in 97.1% of cases and resulting in a very low morbidity rate. Younger GR Class I patients had a significantly higher probability of retaining functional hearing even at the 10-year follow-up; for this reason, the time between symptom onset, diagnosis, and treatment should be shortened to achieve better outcomes in functional hearing preservation.

Treatment of Asymptomatic Meningioma With Gamma Knife Radiosurgery: Long-Term Follow-up With Volumetric Assessment and Clinical Outcome

Neurosurgery ◽  
2019 ◽  
Vol 85 (5) ◽  
pp. E889-E899 ◽  
Author(s):  
Amitabh Gupta ◽  
Zhiyuan Xu ◽  
Or Cohen-Inbar ◽  
M Harrison Snyder ◽  
Landon K Hobbs ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Progression Free Survival ◽  
Tumor Control ◽  
Volumetric Assessment ◽  
Asymptomatic Patients ◽  
Asymptomatic Meningioma ◽  
Longitudinal Imaging

Abstract BACKGROUND Some patients are diagnosed with asymptomatic meningioma(s) after undergoing a screening CT and MRI for minor ailments or postresection. OBJECTIVE To help clinicians in decision making for treatment of asymptomatic meningiomas. METHODS A single center retrospective cohort study of 117 patients with 122 tumors treated with Gamma Knife radiosurgery (GKRS; Elekta AB, Stockholm, Sweden). Patients were followed with longitudinal imaging and clinical evaluations. Tumor volumetry and developments of new signs or symptoms after GKRS were the end points in the study. RESULTS Median patient age at GKRS was 60 yr (range 21-86 yr) with a median clinical follow-up of 53 mo (range 20-252 mo). The median pre-GKRS tumor volume was 3.6 ± 3.8 cc (±standard deviation). Tumors were treated with a median margin dose of 14 ± 2 Gy. At last follow-up, median tumor volume was 2.5 ± 3.6 cc. Radiological progression-free survival (PFS) rates were 97% and 94.4% at 5 yr and 10 yr, respectively. Clinical PFS rates were 86% and 70% at 5 yr and 10 yr, respectively. Development of neurological complications was seen in 21 (18%) patients, and 11 (52%) of them had undergone surgical resection prior to GKRS. CONCLUSION GKRS is a reasonable treatment strategy for asymptomatic meningiomas and compares favorably to natural history studies in terms of tumor control and neurological preservation. It results in relatively low morbidity in previously untreated meningiomas and serves as an appealing alternative treatment modality for recurrent meningiomas in asymptomatic patients.

scholarly journals Gamma Knife radiosurgery in the treatment of abducens nerve schwannomas: a retrospective study

2016 ◽  
Vol 125 (4) ◽  
pp. 832-837 ◽  
Author(s):  
Govindaraju Lakshmi Prasad ◽  
Manish Singh Sharma ◽  
Shashank S. Kale ◽  
Deepak Agrawal ◽  
Manmohan Singh ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Abducens Nerve ◽  
Symptomatic Improvement ◽  
Tumor Control ◽  
Imaging Features ◽  
Intracranial Tumors ◽  
The Mean

OBJECTIVE Of the intracranial schwannomas, those arising from the vestibular nerves are the most common. Abducens nerve (AN) schwannomas are very rare, and there is limited literature on their optimal management. Therapeutic options include surgery and/or stereotactic radiosurgery. The aim of this study was to evaluate the role of Gamma Knife radiosurgery (GKRS) in these sixth cranial nerve (CN) schwannomas. METHODS The authors performed a retrospective analysis of patients who had undergone GKRS for intracranial tumors at their institute in the period from 2003 to 2010. Inclusion criteria were as follows: isolated AN paresis on presentation, a lesion along the course of the sixth CN, and imaging features characteristic of a schwannoma. Patients with other CN deficits and neurofibromatosis Type 2 were excluded. Symptomatic improvement was defined as the resolution of or an improvement in diplopia noted on a subjective basis or as an improvement in lateral eyeball excursion noted objectively on follow-up. A reduction in tumor volume by at least 20%, as noted by comparing the pre- and post-GKRS images, was deemed significant. RESULTS Six patients with a mean age of 37.1 years (range 17–55 years) underwent primary GKRS. There were 2 prepontine cistern, 3 cavernous sinus, and 1 cisterno-cavernous tumor. The mean duration of symptoms was 6.1 months (range 3–12 months). The mean tumor volume was 3.3 cm3 (range 1.5–4.8 cm3). The mean tumor margin radiation dose was 12.5 Gy (range 12–14 Gy), while the median margin dose was 12 Gy (50% isodose line). The median number of isocenters used was 5 (range 4–8). The brainstem received an average 8.35-Gy radiation dosage (range 5.5–11 Gy). The mean follow-up duration was 44.3 months (range 24–78 months). Symptoms remained stable in 1 patient, improved in 3, and resolved in 2 (total improvement 83%). Magnetic resonance imaging at the last follow-up showed a stable tumor size in 3 patients (50%) and a reduction in the other 3. Thus, the tumor control rate achieved was 100%. No new CN deficits were noted. CONCLUSIONS Abducens nerve schwannomas are rare intracranial tumors. They can be cavernous, cisternal, or cisterno-cavernous in location. Excellent tumor control rates and symptomatic improvement can be achieved with GKRS, which appears to be a safe and effective, minimally invasive modality for the treatment of such lesions. Therefore, it is reasonable to consider GKRS as the initial treatment of choice for this rare pathology. Long-term follow-up will be essential for further recommendations.

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