Fractionated stereotactic radiotherapy for the treatment of vestibular schwannomas: combined experience of the Toronto-Sunnybrook Regional Cancer Centre and the Princess Margaret Hospital

Treatment for vestibular schwannoma: Systematic review and single arm meta-analysis

OBJECTIVE

Vestibular schwannoma is a benign tumor in the schwannoma cells of the 8th cranial nerve. It causes symptoms like tinnitus, vertigo and end up with loss of hearing so the appropriate treatment is very important. There are many treatment techniques including conservative, surgery and radiosurgery. We aimed to systematically review and single arm meta-analysis the different treatment techniques of vestibular schwannoma.

METHODS

A comprehensive literature search using thirteen databases including PubMed, Scopus, and Web of Science was performed. All clinical trials about treatment vestibular schwannoma were included and single arm meta-analyzed. We assessed the risk of bias using ROBIN-I's tool and scale of Council Australia's Cancer Guidelines Wiki. The protocol was registered in PROSPERO (CRD42018089784) and has been updated on 17 April 2019.

RESULTS

A total of 35 clinical trials studies were included in the final analysis. The pooled proportion of stable hearing capability in patients receiving gamma knife radiosurgery (GKRS) was 64% (95% CI: 52%-74%). GKRS favored increased hearing capability 10% (95% CI: 7%-16%). Regarding tumor size, GKRS is the most protective method 53% (95% CI: 37%-69%). Complications occurred most commonly in single fractional linac stereotactic radiosurgery (SFSRT) 37% (95% CI: 12%-72%).

CONCLUSION

Our analysis suggested gamma knife radiosurgery could be the most ideal treatment for vestibular schwannoma based on stabilizing hearing capability, increasing hearing capability, decreasing tumor size and complications.

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

Purpose

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

Methods

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

Results

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

Conclusion

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

Fractionated stereotactic radiotherapy of benign skull-base tumors: a dosimetric comparison of volumetric modulated arc therapy with Rapidarc® versus non-coplanar dynamic arcs

Background

Benign tumors of the skull base are a challenge when delivering radiotherapy. An appropriate choice of radiation technique may significantly improve the patient’s outcomes. Our study aimed to compare the dosimetric results of fractionated stereotactic radiotherapy between non-coplanar dynamic arcs and coplanar volumetric modulated arctherapy (Rapidarc®).

Methods

Thirteen patients treated with Novalis TX® were analysed: six vestibular schwannomas, four pituitary adenomas and three meningioma. Two treatment plans were created for each case: dynamic arcs (4–5 non coplanar arcs) and Rapidarc® (2 coplanar arcs). All tumors were >3 cm and accessible to both techniques. Patients had a stereotactic facemask (Brainlab) and were daily repositioned by Exactrac®. GTV and CTV were contoured according to tumor type. A 1-mm margin was added to the CTV to obtain PTV. Radiation doses were 52.2–54 Gy, using 1.8 Gy per fraction. Treatment time was faster with Rapidarc®.

Results

The mean PTV V95 % was 98.8 for Rapidarc® and 95.9 % for DA (p = 0.09). Homogeneity index was better with Rapidarc®: 0.06 vs. 0.09 (p = 0.01). Higher conformity index values were obtained with Rapidarc®: 75.2 vs. 67.9 % (p = 0.04). The volume of healthy brain that received a high dose (V90 %) was 0.7 % using Rapidarc® vs. 1.4 % with dynamic arcs (p = 0.05). Rapidarc® and dynamic arcs gave, respectively, a mean D40 % of 10.5 vs. 18.1 Gy (p = 0.005) for the hippocampus and a Dmean of 25.4 vs. 35.3 Gy (p = 0.008) for the ipsilateral cochlea. Low-dose delivery with Rapidarc® and dynamic arcs were, respectively, 184 vs. 166 cm³ for V20 Gy (p = 0.14) and 1265 vs. 1056 cm³ for V5 Gy (p = 0.67).

Conclusions

Fractionated stereotactic radiotherapy using Rapidarc® for large benign tumors of the skull base provided target volume coverage that was at least equal to that of dynamics arcs, with better conformity and homogeneity and faster treatment time. Rapidarc® also offered better sparing of the ipsilateral cochlea and hippocampus. Low-dose delivery were similar between both techniques.

Fractionated radiation therapy for vestibular schwannoma

Vestibular schwannomas are the most common tumors of the cerebellopontine angle. Multiple management paradigms exist for patients with these benign tumors, including observation, microsurgery, stereotactic radiosurgery, and fractionated radiation therapy, or some combination of these. While the proper course of management is controversial, the goals of therapy are to achieve excellent local tumor control and optimize functional outcomes with as little treatment-related morbidity as possible. Decision-making is tailored to patient-specific factors such as tumor size, clinical presentation, patient age, and goals of hearing preservation. We review the literature in order to summarize the application of fractionated radiation therapy to this tumor entity, where it is used as a primary treatment or, more commonly, as an adjunct therapy. We also provide an overview of the use of fractionated radiation therapy for the preservation of hearing and facial function, and dosing and other technical considerations, in light of the indolent natural history of vestibular schwannomas. We also discuss potential risks associated with this treatment modality, including its effects on temporal bone structures and cranial nerves among other possible complications. Lastly, we outline future directions in this rapidly evolving segment of vestibular schwannoma therapy, which has benefited from the advent of intensity-modulated radiation therapy coupled with stereotactic localization.

Hypofractionated stereotactic radiation therapy in three to five fractions for vestibular schwannoma

OBJECTIVE

To retrospectively examine the outcomes of hypofractionated stereotactic radiation therapy in three to five fractions for vestibular schwannomas.

METHODS

Twenty-five patients with 26 vestibular schwannomas were treated with hypofractionated stereotactic radiation therapy using a CyberKnife. The vestibular schwannomas of 5 patients were associated with type II neurofibromatosis. The median follow-up time was 80 months (range: 6-167); the median planning target volume was 2.6 cm(3) (0.3-15.4); and the median prescribed dose (≥D90) was 21 Gy in three fractions (18-25 Gy in three to five fractions). Progression was defined as ≥2 mm 3-dimensional post-treatment tumor enlargement excluding transient expansion. Progression or any death was counted as an event in progression-free survival rates, whereas only progression was counted in progression-free rates.

RESULTS

The 7-year progression-free survival and progression-free rates were 78 and 95%, respectively. Late adverse events (≥3 months) with grades based on Common Terminology Criteria for Adverse Events, v4.03 were observed in 6 patients: Grade 3 hydrocephalus in one patient, Grade 2 facial nerve disorders in two and Grade 1-2 tinnitus in three. In total, 12 out of 25 patients maintained pure tone averages ≤50 dB before hypofractionated stereotactic radiation therapy, and 6 of these 12 patients (50%) maintained pure tone averages at this level at the final audiometric follow-up after hypofractionated stereotactic radiation therapy. However, gradient deterioration of pure tone average was observed in 11 of these 12 patients. The mean pure tone averages before hypofractionated stereotactic radiation therapy and at the final follow-up for the aforementioned 12 patients were 29.8 and 57.1 dB, respectively.

CONCLUSIONS

Treating vestibular schwannomas with hypofractionated stereotactic radiation therapy in three to five fractions may prevent tumor progression with tolerable toxicity. However, gradient deterioration of pure tone average was observed.

The newly diagnosed vestibular schwannoma: radiosurgery, resection, or observation?

OBJECT

Management recommendations for patients with smaller-volume or newly diagnosed vestibular schwannomas (< 4 cm(3)) need to be based on an understanding of the anticipated natural history of the tumor and the side effects it produces. The natural history can then be compared with the risks and benefits of therapeutic intervention using a minimally invasive strategy such as stereotactic radiosurgery (SRS).

METHODS

The authors reviewed the emerging literature stemming from recent recommendations to "wait and scan" (observation) and compared this strategy with published outcomes after early intervention using SRS or results from matched cohort studies of resection and SRS.

RESULTS

Various retrospective studies indicate that vestibular schwannomas grow at a rate of 0-3.9 mm per year and double in volume between 1.65 and 4.4 years. Stereotactic radiosurgery arrests growth in up to 98% of patients when studied at intervals of 10-15 years. Most patients who select "wait and scan" note gradually decreasing hearing function leading to the loss of useful hearing by 5 years. In contrast, current studies indicate that 3-5 years after Gamma Knife surgery, 61%-80% of patients maintain useful hearing (speech discrimination score > 50%, pure tone average < 50).

CONCLUSIONS

Based on published data on both volume and hearing preservation for both strategies, the authors devised a management recommendation for patients with small vestibular schwannomas. When resection is not chosen by the patient, the authors believe that early SRS intervention, in contrast to observation, results in long-term tumor control and improved rates of hearing preservation.

Dynamic radiosurgery at the Toronto - Bayview Regional Cancer Centre, 1988-2007

Dynamic radiosurgery was first developed in Montreal and was subsequently adopted at the Toronto-Bayview Regional Cancer Centre in 1988. At that time radiosurgery was in its infancy in Canada. The opportunity of offering highly conformal radiation treatments for intracranial targets presented numerous technical challenges notably in the area of quality assurance. This review chronicles the development of radiosurgery at the Toronto-Bayview Regional Cancer Centre and summarises the successes and failures of the program over the following two decades.

Stereotactic Radiosurgery of Cranial Nonvestibular Schwannomas: Results of Single- and Multisession Radiosurgery

BACKGROUND:

Surgical resection of nonvestibular cranial schwannomas carries a considerable risk of postoperative complications. Stereotactic radiosurgery (SRS) offers a non-invasive treatment alternative. The efficacy and safety of multi-session SRS of nonvestibular cranial schwannomas has not been well studied.

OBJECTIVE:

To analyze the results of single- and multi-session SRS of nonvestibular cranial schwannomas.

METHODS:

From 2001 to 2007, 42 lesions in 40 patients were treated with SRS at Stanford University Medical Center, targeting schwannomas of cranial nerves IV (n = 1), V (n = 18), VII (n = 6), X (n = 5), XII (n = 2), jugular foramen (n = 8), and cavernous sinus (n = 2). SRS was delivered to a median marginal dose of 18 Gy (range, 15-33 Gy) in 1 to 3 sessions, targeting a median tumor volume of 3.2 cm3 (range, 0.1-23.7 cm3). The median doses for treatments in 1 (n = 18), 2 (n = 9), and 3 (n = 15) sessions were 17.5, 20, and 18 Gy, respectively.

RESULTS:

With a median follow-up of 29 months (range, 6-84 months), tumor control was achieved in 41 of the 42 lesions. Eighteen of 42 lesions (43%) decreased in size; 23 tumors (55%) remained stable. There were 2 cases of new or worsening cranial nerve deficits in patients treated in single session; no patient treated with multi-session SRS experienced any cranial nerve toxicity (P = 0.18).

CONCLUSION:

SRS of nonvestibular cranial schwannomas provides excellent tumor control with minimal risk of complications. There was a trend towards decreased complications with multi-session SRS.

Predictors of hearing preservation after stereotactic radiosurgery for acoustic neuroma

Object

Many patients with acoustic neuromas (ANs) have hearing function at diagnosis and desire to maintain it. To date, radiosurgical techniques have been focused on conformal irradiation of the tumor mass, with less attention to inner ear structures for which there was scant radiobiological information. The authors of this study evaluated tumor control and hearing preservation as they relate to tumor volume, imaging characteristics, and nerve and cochlear radiation dose following stereotactic radiosurgery (SRS) using the Gamma Knife.

Methods

Seventy-seven patients with ANs had serviceable hearing (Gardner-Robertson [GR] Class I or II) and underwent SRS between 2004 and 2007. This interval reflected more recent measurements of inner ear dosimetry during the authors' 21-year experience. The median patient age was 52 years (range 22–82 years). No patient had undergone any prior treatment for the ANs. The median tumor volume was 0.75 cm3 (range 0.07–7.7 cm3), and the median radiation dose to the tumor margin was 12.5 Gy (range 12–13 Gy). At diagnosis, a greater distance from the lateral tumor to the end of the internal auditory canal correlated with better hearing function.

Results

At a median of 20 months after SRS, no patient required any other additional treatment. Serviceable hearing was preserved in 71% of all patients and in 89% (46 patients) of those with GR Class I hearing. Significant prognostic factors for maintaining the same GR class included (all pre-SRS) GR Class I hearing, a speech discrimination score (SDS) ≥ 80%, a pure tone average (PTA) < 20 dB, and a patient age < 60 years. Significant prognostic factors for serviceable hearing preservation were (all pre-SRS) GR Class I hearing, an SDS ≥ 80%, a PTA < 20 dB, a patient age < 60 years, an intracanalicular tumor location, and a tumor volume < 0.75 cm3. Patients who received a radiation dose of < 4.2 Gy to the central cochlea had significantly better hearing preservation of the same GR class. Twelve of 12 patients < 60 years of age who had received a cochlear dose < 4.2 Gy retained serviceable hearing at 2 years post-SRS.

Conclusions

As currently practiced, SRS with the Gamma Knife preserves serviceable hearing in the majority of patients. Tumor volume and anatomy relate to the hearing level before radiosurgery and influence technique. A low radiosurgical dose to the cochlea enhances hearing preservation.

Advances in technology for intracranial stereotactic radiosurgery

Stereotactic radiosurgery (SRS) refers to a single radiation treatment delivering a high dose to an intra-cranial target localized in three-dimensions by CT and/or MRI imaging. Traditionally, immobilization of the patient's head has been achieved using a rigid stereotactic head frame as the key step in allowing for accurate dose delivery. SRS has been delivered by both Cobalt-60 (Gamma Knife) and linear accelerator (linac) technologies for many decades. The focus of this review is to highlight recent advances and major innovations in SRS technologies relevant to clinical practice and developments allowing for non-invasive frame SRS.

Novalis intensity-modulated radiosurgery: methods for pretreatment planning

OBJECTIVE

The Novalis stereotactic radiotherapy system (BrainLAB, Heimstetten, Germany) allows for precise treatment of cranial base tumors with single-fraction radiosurgery. In some cases, however, proximity of the optic nerve and chiasm is a concern. In these cases, intensity-modulated stereotactic radiosurgery (IMRS) can be used to limit the dose to these structures. IMRS planning can be labor intensive, which poses a problem when it is performed on the day of treatment. We describe our methods and results of preprocedure planning for IMRS for patients with lesions in the cavernous sinus or parasellar regions in whom the dose to the optic nerve or chiasm might exceed our acceptable tolerance dose (8 Gy).

METHODS

Patients whose lesions were more than 4 mm from the optic nerve and chiasm on standard magnetic resonance imaging scans but who were questionable candidates for radiosurgery because of concerns of dose to the optic nerve or chiasm were considered for IMRS. Preprocedure imaging (computed tomography and magnetic resonance imaging) was fused and analyzed using the BrainLAB BrainScan 5.3 treatment planning system. Dynamic conformal arc plans for stereotactic radiosurgery and IMRS were evaluated. Doses to the planning target volume and optic apparatus were assessed by dose-volume histograms and conformality index calculated to characterize the quality of the different plans. When IMRS was used, the preplan allowed for a rapid recalculation on the treatment day, minimizing the time patients were in the head frame before treatment.

RESULTS

We describe three patients with recurrent pituitary tumors and three with meningiomas. Doses were 1500 to 2000 cGy prescribed to the 80 to 96% isodose line delivered by eight to 22 fields. Tumor volumes ranged from 2.70 to 8.82 cm (mean, 5.7 cm). In five of the six patients, the dynamic conformal arc plan precluded delivery of therapeutic dose without exceeding optic nerve tolerance. On the basis of 95% coverage of target volume, maximum prescription doses of 7.7 to 20.64 Gy were possible with the dynamic conformal arc plans without exceeding 8 Gy to the optic apparatus. IMRS allowed maximum doses of 20 to 31 Gy using the same optic apparatus dose restriction. No complications have occurred, and all tumors have remained stable since treatment (mean follow-up period, 30 mo).

CONCLUSION

We believe this pretreatment technique streamlines the process for IMRS, allowing for better patient comfort and efficient physician time use.

Hearing preservation following fractionated stereotactic radiotherapy for vestibular schwannomas: prognostic implications of cochlear dose

Object

The goal in this study was to evaluate hearing preservation rates and to determine prognostic factors for this outcome following fractionated stereotactic radiotherapy (FSRT) of vestibular schwannoma.

Methods

Thirty-four consecutive patients with serviceable hearing who received FSRT between May 1998 and December 2003 were identified. Clinical and audiometry data were collected prospectively. The prescription dose was 45 Gy in 25 fractions prescribed to the 90% isodose line. The median follow-up duration was 36.5 months (range 12–85 months). The actuarial 2- and 4-year local control rates were 100 and 95.7%, respectively. Permanent trigeminal and facial nerve complications were 0 and 6%, respectively. The actuarial 2- and 3-year serviceable hearing preservation rates were both 63%. The median loss in speech reception threshold was 15 dB (range −10 to 65 dB). The radiotherapy dose to the cochlea was the only significant prognostic factor for hearing deterioration. Radiotherapy dose to the cochlear nucleus, patient age, sex, pre-FSRT hearing grade, tumor volume, and intracanalicular tumor volume failed to show any significance as prognostic factors.

Results

Five cases were replanned with four different radiotherapy techniques (namely arcs, dynamic arcs, static conformal fields, and intensity-modulated radiotherapy), with the cochlea defined as an organ at risk. In all cases, replanning resulted in statistically significant reduction in radiation to the cochlea (p = 0.001); however, no single replanning technique was found to be superior.

Conclusions

The radiation dose to the cochlea is strongly predictive for subsequent hearing deterioration. It is essential for the cochlea to be outlined as an organ at risk, and for radiation techniques to be optimized, to improve long-term hearing preservation.

Fractionated stereotactic radiotherapy for acoustic neuroma

BACKGROUND

The clinical outcome and toxicity of fractionated stereotactic radiotherapy (FSRT) was assessed for acoustic neuroma in 60 patients treated in a single institution.

METHODS

Between October 1996 and February 2005, 60 patients received FSRT for acoustic neuroma (AN). The mean total dose applied was 50 Gy in single daily 2-Gy fractions over 5 weeks. The median irradiated tumor volume was 4.9 cm(3) (range, 0.3-49.0 cm(3)). The median follow-up period was 31.9 months.

RESULTS

FSRT was well tolerated in all patients. The 5-year actuarial local control rate was 96.2% (95% CI: 91.1%-100.0%). Five-year actuarial progression-free survival was 92.8% (95% CI: 84.8%-100.0%). The overall hearing preservation rate was 77.3%. Five of 6 patients with initial cranial nerve V (CNV) numbness remained stable post-FSRT. Two of 3 patients with baseline trigeminal neuralgia improved with the remaining patient stable. All 3 patients with nonsurgically related facial nerve weakness either improved or achieved stability in function. There were no cases of new cranial nerve toxicity post-FSRT.

CONCLUSIONS

FSRT for the treatment of AN is safe, effective, and well tolerated. FSRT should thus be considered as an effective alternative treatment modality when compared with microsurgical resection or single fraction stereotactic radiosurgery.

Twenty years' experience in the treatment of acoustic neuromas with fractionated radiotherapy: a review of 45 cases

PURPOSE

To evaluate very long-term results of fractionated radiotherapy (FRT) of acoustic neuromas (AN).

METHODS AND MATERIALS

From January 1986 to January 2004, FRT was performed in 45 consecutive patients (46 AN). Indications were as follows: poor general condition contraindicating surgery, hearing preservation in bilateral neuromas, partial resection, nonsurgical recurrence. A 3-field to 5-field technique with static beams was used. A mean total dose of 51 Gy was given (1.80 Gy/fraction). The median tumor diameter was 31 mm (range, 11-55 mm). The median follow-up from FRT was 80 months (range, 4-227 months).

RESULTS

The particularity of our series consists of a very long-term follow-up of FRT given to selected patients. Nineteen patients died, two with progressive disease, and 17 from non-AN causes. A serviceable level of hearing was preserved in 7/9 hearing patients. No patient had facial or trigeminal neuropathy. Tumor shrinkage was observed in 27 (59%) and stable disease in 16 (35%). Tumor progression occurred in three patients, 12 to 15 months after FRT. Two additional tumors recurred after shrinkage 20 and 216 months after treatment and were operated on. Actuarial local tumor control rates at 5 and 15 years were 86%. For the patient who had a tumor recurrence at 216 months, histologic examination documented transformation to a low-grade malignant peripheral nerve sheath tumor.

CONCLUSION

Very long-term efficacy of FRT is well documented in this series. However, our results suggest that malignant transformation can occur many years after FRT so we advocate caution when using this treatment for young patients.

Vestibular schwannoma management: What is the 'best' option?

There is an abundance of medical literature describing the management options for vestibular schwannomas. However, the lack of high quality clinical trials means that, for any individual patient, the decision is often based on the clinician's personal biases. The management options that are available are conservative treatment, surgery, single-dose stereotactic radiosurgery and fractionated radiotherapy. In this review, we set out what the aims of managing a vestibular schwannoma should be and compare how these different treatment modalities perform. The particular objectives of tumour control, cranial nerve preservation, prevention of malignancy, quality of life and cost-effectiveness are discussed. It remains difficult to differentiate between these methods when more than one is suitable; the literature confirms that they are all safe and effective, but the decision must be the patient's, based on their individual priorities. This review should equip the clinician to provide an informed overview of the options.

Management of acoustic neuromas with fractionated stereotactic radiotherapy (FSRT): Long-term results in 106 patients treated in a single institution

PURPOSE

To assess the long-term outcome and toxicity of fractionated stereotactic radiotherapy for acoustic neuromas in 106 patients treated in a single institution.

PATIENTS AND METHODS

Between October 1989 and January 2004, fractionated stereotactic radiotherapy (FSRT) was performed in 106 patients with acoustic neuroma (AN). The median total dose applied was 57.6 Gy in median single fractions of 1.8 Gy in five fractions per week. The median irradiated tumor volume was 3.9 mL (range, 2.7-30.7 mL). The median follow-up time was 48.5 months (range, 3-172 months).

RESULTS

Fractionated stereotactic radiotherapy was well tolerated in all patients. Actuarial local tumor control rates at 3- and 5- years after FSRT were 94.3% and 93%, respectively. Actuarial useful hearing preservation was 94% at 5 years. The presence of neurofibromatosis (NF-2) significantly adversely influenced hearing preservation in patients that presented with useful hearing at the initiation of RT (p = 0.00062). Actuarial hearing preservation without the diagnosis of NF-2 was 98%. In cases with NF-2, the hearing preservation rate was 64%. Cranial nerve toxicity other than hearing impairment was rare. The rate of radiation induced toxicity to the trigeminal and facial nerve was 3.4% and 2.3%, respectively.

CONCLUSION

Fractionated stereotactic radiotherapy is safe and efficacious for the treatment of AN, with mild toxicity with regard to hearing loss and cranial nerve function. FSRT might be considered as an equieffective treatment modality compared to neurosurgery and therefore represents an interesting alternative therapy for patients with AN.

Stereotactic Radiotherapy for Vestibular Schwannomas: Favorable Outcome with Minimal Toxicity

OBJECTIVE:

To determine the outcome and toxicity in patients with vestibular schwannomas treated with conventionally fractionated stereotactic radiotherapy (SRT) and to identify prognostic factors that are predictive of outcome.

METHODS:

Between 1992 and 2001, 70 patients with vestibular schwannomas were treated with linear accelerator-based SRT in our institutions. Eleven patients had neurofibromatosis Type II (NF2). The median age was 53 years (range, 17–82 yrs). The median tumor volume was 2.4 cm3 (range, 0.05–21.1 cm3). The indications for SRT were distributed as follows: 47% newly diagnosed, 31% progressive tumors after watchful waiting, 3% adjuvant postoperative radiation, and 19% recurrent tumors after surgical resection. The median dose was 54 Gy in 1.8 Gy per fraction, prescribed to 95% of the isodose line. Relocatable stereotactic frames were used for daily treatments. The median follow-up was 45.3 months.

RESULTS:

Tumor recurrence was defined as progressive enlargement of tumor on follow-up magnetic resonance imaging studies. One patient had a tumor recurrence at 38 months after SRT. The actuarial tumor control rates were 100 and 98% at 3 and 5 years, respectively. Three patients with a median tumor volume of 16.2 cm3 required surgical resection for persistent or increasing symptoms at a median of 37 months. The actuarial freedom from resection rates were 98 and 92% at 3 and 5 years, respectively. In multivariate analysis, tumor volume at time of treatment was predictive for neurosurgical intervention (surgical resection or shunt placement) after SRT (P = 0.001). The 3- and 5-year actuarial rates of freedom from any neurosurgical intervention were 100 and 97% for patients with tumor volume less than 8 cm3 and 74 and 47% respectively for patients with tumor of at least 8 cm3 (P &lt; 0.0001). The 3-year actuarial rates of facial and trigeminal nerve preservation were 99 and 96%, respectively. Surgery before SRT was predictive of posttreatment trigeminal neuropathy. The 3-year actuarial rates of freedom from trigeminal neuropathy were 86 and 98% for patients with and without previous resection, respectively (P = 0.04). There was no difference in tumor control and cranial nerve function preservation rates seen in NF2 patients compared with non-NF2 patients. No second primary cancer or malignant transformation was observed.

CONCLUSION:

SRT in the conventionally fractionated approach results in a very favorable outcome with minimal toxicity, with results comparable to those of the best of the radiosurgery series. Patients with large tumors are more likely to undergo neurosurgical interventions after SRT. Patients who have undergone previous surgery are at increased risk of developing trigeminal neuropathy.

Staged Stereotactic Irradiation for Acoustic Neuroma

OBJECTIVE:

Stereotactic radiosurgery has proven effective in the treatment of acoustic neuromas. Prior reports using single-stage radiosurgery consistently have shown excellent tumor control, but only up to a 50 to 73% likelihood of maintaining hearing at pretreatment levels. Staged, frame-based radiosurgery using 12-hour interfraction intervals previously has been shown by our group to achieve excellent tumor control while increasing the rate of hearing preservation at 2 years to 77%. The arrival of CyberKnife (Accuray, Inc., Sunnyvale, CA) image-guided radiosurgery now makes it more practical to treat acoustic neuroma with a staged approach. We hypothesize that such factors may further minimize injury of adjacent cranial nerves. In this retrospective study, we report our experience with staged radiosurgery for managing acoustic neuromas.

METHODS:

Since 1999, the CyberKnife has been used to treat more than 270 patients with acoustic neuroma at Stanford University. Sixty-one of these patients have now been followed up for a minimum of 36 months and form the basis for the present clinical investigation. Among the treated patients, the mean transverse tumor diameter was 18.5 mm, whereas the total marginal dose was either 18 or 21 Gy using three 6- or 7-Gy fractions. Audiograms and magnetic resonance imaging were obtained at 6-months intervals after treatment for the first 2 years and then annually thereafter.

RESULTS:

Of the 61 patients with a minimum of 36 months of follow-up (mean, 48 mo), 74% of patients with serviceable hearing (Gardner-Robinson Class 1–2) maintained serviceable hearing at the last follow-up, and no patient with at least some hearing before treatment lost all hearing on the treated side. Only one treated tumor (2%) progressed after radiosurgery; 29 (48%) of 61 decreased in size and 31 (50%) of the 61 tumors were stable. In no patients did new trigeminal dysfunction develop, nor did any patient experience permanent injury to their facial nerve; two patients experienced transient facial twitching that resolved in 3 to 5 months.

CONCLUSION:

Although still preliminary, these results indicate that improved tumor dose homogeneity and a staged treatment regimen may improve hearing preservation in acoustic neuroma patients undergoing stereotactic radiosurgery.

Radiosurgery of vestibular schwannomas: summary of experience in 829 cases

OBJECT

Management options for vestibular schwannomas (VSs) have greatly expanded since the introduction of stereotactic radiosurgery. Optimal outcomes reflect long-term tumor control, preservation of cranial nerve function, and retention of quality of life. The authors review their 15-year experience.

METHODS

Between 1987 and 2002, some 829 patients with VSs underwent gamma knife surgery (GKS). Dose selection, imaging, and dose planning techniques evolved between 1987 and 1992 but thereafter remained stable for 10 years. The average tumor volume was 2.5 cm3. The median margin dose to the tumor was 13 Gy (range 10-20 Gy). No patient sustained significant perioperative morbidity. The average duration of hospital stay was less than 1 day. Unchanged hearing preservation was possible in 50 to 77% of patients (up to 90% in those with intracanalicular tumors). Facial neuropathy risks were reduced to less than 1%. Trigeminal symptoms were detected in less than 3% of patients whose tumors reached the level of the trigeminal nerve. Tumor control rates at 10 years were 97% (no additional treatment needed).

CONCLUSIONS

Superior imaging, multiple isocenter volumetric conformal dose planning, and optimal precision and dose delivery contributed to the long-term success of GKS, including in those patients in whom initial microsurgery had failed. Gamma knife surgery provides a low risk, minimally invasive treatment option for patients with newly diagnosed or residual VS. Cranial nerve preservation and quality of life maintenance are possible in long-term follow up.

Radiosurgery of vestibular schwannomas: summary of experience in 829 cases

Object. Management options for vestibular schwannomas (VSs) have greatly expanded since the introduction of stereotactic radiosurgery. Optimal outcomes reflect long-term tumor control, preservation of cranial nerve function, and retention of quality of life. The authors review their 15-year experience.

Methods. Between 1987 and 2002, some 829 patients with VSs underwent gamma knife surgery (GKS). Dose selection, imaging, and dose planning techniques evolved between 1987 and 1992 but thereafter remained stable for 10 years. The average tumor volume was 2.5 cm3. The median margin dose to the tumor was 13 Gy (range 10–20 Gy).

No patient sustained significant perioperative morbidity. The average duration of hospital stay was less than 1 day. Unchanged hearing preservation was possible in 50 to 77% of patients (up to 90% in those with intracanalicular tumors). Facial neuropathy risks were reduced to less than 1%. Trigeminal symptoms were detected in less than 3% of patients whose tumors reached the level of the trigeminal nerve. Tumor control rates at 10 years were 97% (no additional treatment needed).

Conclusions. Superior imaging, multiple isocenter volumetric conformal dose planning, and optimal precision and dose delivery contributed to the long-term success of GKS, including in those patients in whom initial microsurgery had failed. Gamma knife surgery provides a low risk, minimally invasive treatment option for patients with newly diagnosed or residual VS. Cranial nerve preservation and quality of life maintenance are possible in long-term follow up.

Hearing preservation after gamma knife stereotactic radiosurgery of vestibular schwannoma

BACKGROUND

To evaluate the hearing preservation rate and to determine its prognostic factors after gamma knife (GK) stereotactic radiosurgery (SRS) in patients with vestibular schwannoma, the authors used a prospective study design to analyze these patients.

METHODS

Between December 1997 and January 2002, 25 patients with vestibular schwannoma with serviceable hearing were enrolled in the current study. The median tumor volume was 3.0 cc (0.16-9.1 cc). The prescription dose was 12.0 +/- 0.7 gray at an isodose line of 49.8 +/- 1.1%. The tumor control rate and complications were evaluated by focusing on hearing preservation and its prognostic factors.

RESULTS

Based on radiologic study, the tumor control rate was 92% during the median follow-up period of 45 months. The trigeminal and facial nerve preservation rates were 95% and 100%, respectively. Thirteen (52%) of the 25 patients preserved serviceable hearing and 9 (36%) patients retained their pre-GK G-R grade levels after GK SRS. However, 16 patients showed hearing deterioration > 20 dB within 3-6 months and this trend continued for 24 months after the treatment. The maximum radiotherapy dose delivered to the cochlear nucleus was the single, significant prognostic factor of hearing deterioration.

CONCLUSIONS

The authors concluded that a more sophisticated strategy to prevent hearing deterioration during the first 6 months post-GK SRS is necessary to improve long-term hearing preservation.

Audiologic and treatment outcomes after linear accelerator–based stereotactic irradiation for acoustic neuroma

PURPOSE

Although surgical excision is the traditional treatment modality for acoustic neuroma, radiotherapy (RT) is gaining momentum as an alternative. This is particularly evident in patients with useful hearing, in whom fractionated RT offers the potential for hearing preservation. Our objective was to determine the disease control, hearing preservation (via audiograms), and toxicity rates after linear accelerator-based stereotactic radiation for acoustic neuroma.

METHODS AND MATERIALS

A total of 72 acoustic neuroma patients underwent stereotactic irradiation and had at least 6 months of follow-up between October 1997 and March 2002. Of these, 45 received single-fraction stereotactic radiosurgery (SRS) and 27 received fractionated stereotactic radiotherapy (SRT). Before treatment, all SRS patients were functionally deaf and 23 of 25 SRT patients had useful hearing in the affected ear. The minimal peripheral dose was 12 Gy and 45 Gy in all SRS and SRT patients, respectively. Tumor control, toxicity, and hearing preservation were recorded.

RESULTS

The median follow-up in the SRS and SRT groups was 27 and 26 months, respectively. No tumor progression was seen after SRS and SRT. On the basis of the audiogram criteria, the 1-year and 2-year hearing preservation rate was 85% and 57%, respectively. The mean pre- and post-SRT speech recognition threshold was 20 and 38 dB, respectively. The mean proportion of pre- and post-SRT speech discrimination was 91% and 59%, respectively.

CONCLUSION

Stereotactic RT achieves good local control, with acceptable toxicity. RT fractionation appears to provide encouraging rates of hearing preservation.

Management of acoustic schwannoma

PURPOSE

To discuss the optimal management for patients with acoustic schwannoma.

MATERIALS AND METHODS

Review of the pertinent literature.

RESULTS

Microsurgery, stereotactic radiosurgery, and fractionated radiotherapy result in cure rates that approximate 90% at 5 years. Depending on tumor extent and surgical approach, the morbidity of microsurgery may exceed that of stereotactic radiosurgery and fractionated radiotherapy. Patients with useful hearing before treatment may have a higher likelihood of hearing preservation after radiotherapy compared with radiosurgery.

CONCLUSION

Both microsurgery and radiosurgery are good options for patients with tumors less than 3 cm. Depending on tumor extent and the surgical approach, the morbidity of microsurgery may exceed that of radiosurgery. Patients with useful hearing may have a higher likelihood of hearing preservation after radiotherapy. Microsurgery is preferred for patients in whom the disease progresses after initial irradiation and in patients with tumors larger than 3 cm.

Single-fraction vs. fractionated linac-based stereotactic radiosurgery for vestibular schwannoma: a single-institution study

PURPOSE

In this single-institution trial, we investigated whether fractionated stereotactic radiation therapy is superior to single-fraction linac-based radiosurgery with respect to treatment-related toxicity and local control in patients with vestibular schwannoma.

METHODS AND MATERIALS

All 129 vestibular schwannoma patients treated between 1992 and June 2000 at our linac-based radiosurgery facility were analyzed with respect to treatment schedule. Dentate patients were prospectively selected for a fractionated schedule of 5 x 4 Gy and later on 5 x 5 Gy at the 80% isodose in 1 week with a relocatable stereotactic frame. Edentate patients were prospectively selected for a nonfractionated treatment of 1 x 10 Gy and later on 1 x 12.5 Gy at 80% isodose with an invasive stereotactic frame. Both MRI and CT scans were made in all 129 patients within 1 week before treatment. All patients were followed yearly with MRI and physical examination.

RESULTS

A fractionated schedule was given to 80 patients and a single fraction to 49 patients. Mean follow-up time was 33 months (range: 12-107 months). There was no statistically significant difference between the single-fraction group and the fractionated group with respect to mean tumor diameter (2.6 vs. 2.5 cm) or mean follow-up time (both 33 months). Only mean age (63 years vs. 49 years) was statistically significantly different (p = 0.001). Outcome differences between the single-fraction treatment group and the fractionated treatment group with respect to 5-year local control probability (100% vs. 94%), 5-year facial nerve preservation probability (93% vs. 97%), and 5-year hearing preservation probability (75% vs. 61%) were not statistically significant. The difference in 5-year trigeminal nerve preservation (92% vs. 98%) reached statistical significance (p = 0.048).

CONCLUSION

Linac-based single-fraction radiosurgery seems to be as good as linac-based fractionated stereotactic radiation therapy in vestibular schwannoma patients, except for a small difference in trigeminal nerve preservation rate in favor of a fractionated schedule.