Toward Dose Optimization for Fractionated Stereotactic Radiotherapy for Acoustic Neuromas: Comparison of Two Dose Cohorts

Hypoglossal nerve delineation in nasopharyngeal carcinoma patients may reduce the radiation dose and damage to the nerve

This study aims to establish a delineation guideline for the contouring of the hypoglossal nerve by dividing the nerve into different segments, and to test the possibility of a radiation dose reduction to the hypoglossal nerve in NPC patients receiving radiotherapy. Twenty NPC patients were selected arbitrarily. The hypoglossal nerves were delineated using anatomic landmarks and divided into the cisternal, intracanalicular, carotid, and transverse segments. The tumor coverage by radiation and dose-volume parameters of the nerve with and without various dose constraints to the hypoglossal nerve were compared. The hypoglossal nerve, which is invisible on CT images, can be delineated accurately with the assistance of several anatomic landmarks. Without a dose constraint to the hypoglossal nerve, the carotid space, intracanalicular, and transverse segments had high radiation dose-volumes. The dose-volume to the nerve, however, can be reduced when the nerve was defined and a dose constraint was given. The delineation of the hypoglossal nerve with its different segments is feasible. The carotid space, intracanalicular, and transverse segments received the highest dose, where the nerve damage was most likely located. The dose to the nerve can be reduced to less than 70 Gy using the intensity-modulated radiotherapy technique.

Proton beam radiation therapy for vestibular schwannomas-tumor control and hearing preservation rates: a systematic review and meta-analysis

OBJECTIVE

Proton beam therapy is considered, by some authors, as having the advantage of delivering dose distributions more conformal to target compared with stereotactic radiosurgery (SRS). Here, we performed a systematic review and meta-analysis of proton beam for VSs, evaluating tumor control and cranial nerve preservation rates, particularly with regard to facial and hearing preservation.

METHODS

We reviewed, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) articles published between 1968 and September 30, 2022. We retained 8 studies reporting 587 patients.

RESULTS

Overall rate of tumor control (both stability and decrease in volume) was 95.4% (range 93.5-97.2%, p heterogeneity= 0.77, p<0.001). Overall rate of tumor progression was 4.6% (range 2.8-6.5%, p heterogeneity < 0.77, p<0.001). Overall rate of trigeminal nerve preservation (absence of numbness) was 95.6% (range 93.5-97.7%, I2 = 11.44%, p heterogeneity= 0.34, p<0.001). Overall rate of facial nerve preservation was 93.7% (range 89.6-97.7%, I2 = 76.27%, p heterogeneity<0.001, p<0.001). Overall rate of hearing preservation was 40.6% (range 29.4-51.8%, I2 = 43.36%, p heterogeneity= 0.1, p<0.001).

CONCLUSION

Proton beam therapy for VSs achieves high tumor control rates, as high as 95.4%. Facial rate preservation overall rates are 93%, which is lower compared to the most SRS series. Compared with most currently reported SRS techniques, proton beam radiation therapy for VSs does not offer an advantage for facial and hearing preservation compared to most of the currently reported SRS series.

Schwannomas of Brain and Spinal Cord

Schwannomas are benign tumors originating from the Schwann cells of cranial or spinal nerves. The most common cranial schwannomas originate from the eight cranial nervevestibular schwannomas (VS). VS account for 6-8% of all intracranial tumors, 25-33% of the tumors localized in the posterior cranial fossa, and 80-94% of the tumors in the cerebellopontine angle (CPA). Schwannomas of other cranial nerves/trigeminal, facial, and schwannomas of the lower cranial nerves/are much less frequent. According to the World Health Organization (WHO), intracranial and intraspinal schwannomas are classified as Grade I. Some VS are found incidentally, but most present with hearing loss (95%), tinnitus (63%), disequilibrium (61%), or headache (32%). The neurological symptoms of VSs are mainly due to compression on the surrounding structures, such as the cranial nerves and vessels, or the brainstem. The gold standard for the imaging diagnosis of VS is MRI scan. The optimal management of VSs remains controversial. There are three main management options-conservative treatment or "watch-and-wait" policy, surgical treatment, and radiotherapy in all its variations. Currently, surgery of VS is not merely a life-saving procedure. The functional outcome of surgery and the quality of life become issues of major importance. The most appropriate surgical approach for each patient should be considered according to some criteria including indications, risk-benefit ratio, and prognosis of each patient. The approaches to the CPA and VS removal are generally divided in posterior and lateral. The retrosigmoid suboccipital approach is a safe and simple approach, and it is favored for VS surgery in most neurosurgical centers. Radiosurgery is becoming more and more available nowadays and is established as one of the main treatment modalities in VS management. Radiosurgery (SRS) is performed with either Gamma knife, Cyber knife, or linear accelerator. Larger tumors are being increasingly frequently managed with combined surgery and radiosurgery. The main goal of VS management is preservation of neurological function - facial nerve function, hearing, etc. The reported recurrence rate after microsurgical tumor removal is 0.5-5%. Postoperative follow-up imaging is essential to diagnose any recurrence.

Guidelines in the management of CNS tumors

INTRODUCTION

Evidence-based, clinical practice guidelines in the management of central nervous system tumors (CNS) continue to be developed and updated through the work of the Joint Section on Tumors of the Congress of Neurological Surgeons (CNS) and the American Association of Neurological Surgeons (AANS).

METHODS

The guidelines are created using the most current and clinically relevant evidence using systematic methodologies, which classify available data and provide recommendations for clinical practice.

CONCLUSION

This update summarizes the Tumor Section Guidelines developed over the last five years for non-functioning pituitary adenomas, low grade gliomas, vestibular schwannomas, and metastatic brain tumors.

Long-Term Hearing Outcomes Following Stereotactic Radiosurgery in Vestibular Schwannoma Patients-A Retrospective Cohort Study

BACKGROUND

An understanding of the hearing outcomes is needed for treatment counseling for patients with vestibular schwannomas (VS).

OBJECTIVE

To determine long-term hearing results following stereotactic radiosurgery (SRS) for VS and identify any influential variables.

METHODS

Tertiary hospital retrospective cohort.

RESULTS

There were 579 tumors (576 patients) treated with SRS. Eighty-two percent (473) of tumors had ≥1 yr and 59% (344 ≥3 yr follow-up. In the 244 tumor ears, with measurable hearing before SRS who were followed ≥1 yr, 14% (31) had improved hearing, 13% (29) unchanged hearing, and 74% (158) had worsened hearing. In 175 patients with ≥3 yr follow-up and who had measurable hearing pretreatment, 6% (11 ears) improved hearing, 31% (54 ears) unchanged hearing, and 63% (110 ears) had worsened hearing. Patients with tumors with larger target volumes (P = .040) and with neurofibromatosis type 2 (NF2; P = .017) were associated with poorer hearing (P = .040). Patients with word recognition scores (WRS) of 50% or poorer had tumors with a larger volume (P = .0002), larger linear size (P = .032), and NF2 (P = .045). Traditionally reported hearing outcomes using the Gardner Robertson maintenance of PTA ≤50 db or WRS ≥50% were 48% at 3 yr, which overestimates hearing outcomes compared to the above reporting standards.

CONCLUSION

Hearing declines over time in VS treated with SRS in a high proportion of cases. The frequency and magnitude of long-term hearing decline following SRS argues against prophylactic radiation for small tumors in hearing ears with undetermined growth behavior.

Fractionated Proton Beam Therapy for Acoustic Neuromas: Tumor Control and Hearing Preservation

Purpose

This prospective cohort evaluated patients with acoustic neuroma treated with proton irradiation at Loma Linda University Medical Center. A dose of 50.4 Gy in 28 fractions was given to improve hearing preservation while maintaining tumor control.

Patients and Methods

Ninety-five patients were treated from March 1991 to March 2008. Fractionated proton radiotherapy at daily doses of 1.8 Gy was employed. Patients were treated to 1 of 3 total doses: 59.4 Gy, used initially for patients without serviceable hearing; 54 Gy, used for patients with serviceable hearing through October 2000; and 50.4 Gy used since 2001 for patients with serviceable hearing. Survival and local control were calculated using the Kaplan-Meier method. Logistic regression analysis was preformed comparing dose, tumor size, and tumor location with hearing preservation.

Results

Ninety-four patients were assessable; the median follow-up was 64 months. Five-year local control rates for the 59.4 Gy, 54 Gy, and 50.4 Gy groups were 95%, 97%, and 92%, respectively (P = .80); the overall 10-year actuarial control rate was 90%. Cranial nerve injuries occurred in <5% in all groups. Four-year actuarial rates of hearing preservation were maintained in 44% of patients treated with 54 Gy and 64% treated with 50.4 Gy (P = .284). On multivariate analysis, initial tumor diameter (≤1.5 cm) was found to be a prognostic factor for maintaining serviceable hearing in both groups (P = .011).

Conclusions

Fractionated proton therapy of 50.4 Gy offers excellent local control and minimal cranial nerve toxicities. Improved rates of hearing preservation that are comparable with radiosurgery were seen with 50.4 Gy compared with higher doses, although this did not reach significance. Maintaining hearing was found to be associated with smaller initial tumor size.

Long-Term Outcomes of Fractionated Stereotactic Proton Therapy for Vestibular Schwannoma: A Case Series

Purpose

Evaluate clinical outcomes in patients with vestibular schwannoma (VS) treated with fractionated proton therapy (PT) at a single institution.

Materials and Methods

We retrospectively reviewed the medical records of patients treated with fractionated PT for definitive management of VS between November 2007 and December 2013 at our institution. No patient had received prior treatment for VS. Patients received 50.4 Gy in 28 fractions using passively scattered PT. Pretreatment and posttreatment hearing status, tumor dimensions, and cranial nerve V and VII function were evaluated. Hearing status was graded as nonserviceable or serviceable, defined as Gardner-Robertson grade I or II and the ability to use a telephone with the treated ear. Toxicities were prospectively evaluated using Common Terminology Criteria for Adverse Events, version 4.0.

Results

Fourteen patients with 14 lesions (8 men, 6 women) were included in the analysis. Median age at treatment was 60 years (range, 24-74 years). Median clinical follow-up for living patients was 68 months (range, 36-106 months). Mean maximal tumor dimension was 2.1 cm (range, 0.5-3.8 cm). Mean tumor volume was 6.4 cm³ (range, 0.3-16.0 cm³). One patient died of unrelated causes 5 months after treatment, and 2 had subsequent surgical resections due to radiographic and/or clinical progression. The actuarial 3-year local control rate was 85%. There were no cranial nerve V or VII injuries. Two of 6 patients (33%) with serviceable hearing at the time of treatment retained serviceable hearing. Three patients (21%) demonstrated radiographic tumor regression on brain magnetic resonance imaging after a median of 26 months (range, 2-113 months). No acute toxicity of grade 3 or above was reported.

Conclusion

Fractionated PT for VS is well tolerated and provides good local control. Improvements in proton delivery techniques and patient selection may enable improved outcomes.

Low-Dose Gamma Knife Radiosurgery for Vestibular Schwannomas: Tumor Control and Cranial Nerve Function Preservation After 11 Gy

OBJECTIVES

This study aims to report tumor control rates and cranial nerve function after low dose (11.0 Gy) Gamma knife radiosurgery (GKRS) in patients with vestibular schwannomas.

METHODS

A retrospective chart review was performed on 30 consecutive patients with vestibular schwannomas treated from March 2004 to August 2010 with GKRS at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. The marginal dose for all patients was 11.0 Gy prescribed to the 50% isodose line. Median follow-up time was 42 months. The median treatment volume was 0.53 cm3. Hearing data were obtained from audiometry reports before and after radiosurgery.

RESULTS

The actuarial progression free survival (PFS) based on freedom from surgery was 100% at 5 years. PFS based on freedom from persistent growth was 91% at 5 years. One patient experienced tumor progression requiring resection at 87 months. Serviceable hearing, defined as Gardner-Robertson score of I-II, was preserved in 50% of patients. On univariate and multivariate analyses, only higher mean and maximum dose to the cochlea significantly decreased the proportion of patients with serviceable hearing.

CONCLUSION

Vestibular schwannomas can be treated with low doses (11.0 Gy) of GKRS with good tumor control and cranial nerve preservation.

Vestibular Schwannomas Treated with Cyberknife®: Clinical Outcomes

Purpose

Fractionated stereotactic radiotherapy (FSR) is a recognized treatment for vestibular schwannomas (VS). This study's aim is to present clinical outcomes and local control (LC) results for patients with VS treated with FSR using the Cyberknife® (CK) in 2 French cancer centers.

Methods

Patients treated with FSR for VS between 2007 and 2012 were retrospectively analyzed. Local control was determined using follow-up MRI. The hearing preservation (HP) rate was determined by analyzing pretreatment and posttreatment audiograms.

Results

Forty patients were treated for VS with the CK in both centers. The mean maximal VS dimension was 18.3 mm (range 3–30). The median follow-up was 36 months and the LC was 97% at 3 years of follow-up and 89% after 5 years. The HP rate was 83% and no facial nerve impairment was reported.

Conclusions

Our results in terms of LC and HP rate are congruent with similar studies that use the CK to treat VS. It appears that the CK is safe and efficient in VS management even for large lesions. Further studies with larger cohorts are warranted.

Schwannoma of the trochlear nerve-an illustrated case series and a systematic review of management

Schwannomas of cranial nerves in the absence of systemic neurofibromatosis are relatively rare. Among these, schwannomas of the trochlear nerve are even less common. They can be found incidentally or when they cause diplopia or other significant neurological deficits. Treatment options include observation only, neuro-ophthalmological intervention, and/or neurosurgical management via resection or sterotactic radiosurgery (SRS). In recent years, the latter has become an attractive therapeutic tool for a number of benign skull base neoplasm including a small number of reports on its successful use for trochlear Schwannomas. However, no treatment algorithm for the management of these tumors has been proposed so far. The goal of this manuscript is to illustrate a case series of this rare entity and to suggest a rational treatment algorithm for trochlear schwannomas, based on our institutional experience of recent cases, and a pertinent review of the literature. Including our series of 5 cases, a total of 85 cases reporting on the management of trochlear schwannomas have been published. Of those reported, less than half (40 %) of patients underwent surgical resection, whereas the remainder were managed conservatively or with SRS. Seventy-six percent (65/85) of the entire cohort presented with diplopia, which was the solitary symptom in over half of the cases (n = 39). All patients who presented with symptoms other than diplopia or headaches as solitary symptoms underwent surgical resection. Patients in the non-surgical group were mostly male (M/F = 3.5:1), presented at an older age and had shorter mean diameter (4.6 vs. 30.4 mm, p < 0.0001) when compared to the surgical group. Twelve patients in the entire cohort were treated with SRS, none of whom had undergone surgical resection before or after radiation treatment. Trochlear schwannoma patients without systemic neurofibromatosis are rare and infrequently reported in the literature. Of those, patients harboring symptomatic trochlear Schwannomas do not form a single homogenous group, but fall into two rather distinct subgroups regarding demographics and clinical characteristics. Among those patients in need of intervention, open microsurgical resection as well as less invasive treatment options exist, which all aim at safe relief of symptoms and prevention of progression. Both open microsurgical removal as well as SRS can achieve good long-term local control. Consequently, a tailored multidisciplinary treatment algorithm, based on the individual presentation and tumor configuration, is proposed.

Reduced-dose fractionated stereotactic radiotherapy for acoustic neuromas: maintenance of tumor control with improved hearing preservation

BACKGROUND

Fractionated stereotactic radiotherapy (FSRT) is a noninvasive treatment for acoustic neuromas (ANs). Initial reports from our institution demonstrated that the reduction of treatment dose to 46.8 Gy resulted in improved preservation of functional hearing status.

OBJECTIVE

We now report the tumor control (TC), symptomatic outcome, and hearing preservation (HP) rate in patients treated with reduced-dose FSRT.

METHODS

We analyzed all patients with AN treated from 2002 to 2011. All patients received 46.8 Gy in 1.8-Gy fractions. Follow-up audiogram and magnetic resonance imaging were performed in ≤ 1-year intervals. TC and HP were calculated by the Kaplan-Meier method. Analysis of HP, defined as Gardner-Robertson value ≤ 2, was determined by audiometric data. Non-hearing-related symptoms were defined by Common Terminology Criteria for Adverse Events version 4.

RESULTS

In total, 154 patients were analyzed. At a median follow-up of 35 months (range, 4-108), TC was achieved in 96% of patients (n = 148/154) and at 3 and 5 years was 99% and 93%. Eighty-seven patients had serviceable hearing at the time of FSRT and evaluable audiometric follow-up. Overall HP was 67% and at 3 and 5 years was 66% and 54%. Pure tone average decreased by a median of 13 dB in all patients. Nineteen percent (n = 31) of patients experienced symptom improvement, and 8% (n = 13) had worsening of symptoms. Cranial nerve dysfunction occurred in 3.8% of patients (n = 6).

CONCLUSION

Reduced-dose FSRT to 46.8 Gy for AN achieves excellent functional HP rates and limited toxicity without compromising long-term TC. Based on these promising outcomes, further attempts at dose deescalation may be warranted.

Single institution experience treating 104 vestibular schwannomas with fractionated stereotactic radiation therapy or stereotactic radiosurgery

The pupose of this study is to assess the long-term outcome and toxicity of fractionated stereotactic radiation therapy (FSRT) and stereotactic radiosurgery (SRS) for 100 vestibular schwannomas treated at a single institution. From 1993 to 2007, 104 patients underwent were treated with radiation therapy for vestibular schwannoma. Forty-eight patients received SRS, with a median prescription dose of 12.5 Gy for SRS (range 9.7-16 Gy). For FSRT, two different fraction schedules were employed: a conventional schedule (ConFSRT) of 1.8 Gy per fraction (Gy/F) for 25 or 28 fractions to a total dose of 45 or 50.4 Gy (n = 19); and a once weekly hypofractionated course (HypoFSRT) consisting of 4 Gy/F for 5 fractions to a total dose of 20 Gy (n = 37). Patients treated with FSRT had better baseline hearing, facial, and trigeminal nerve function, and were more likely to have a diagnosis of NF2. The 5-year progression free rate (PFR) was 97.0 after SRS, 90.5% after HypoFSRT, and 100.0% after ConFSRT (p = NS). Univariate analysis demonstrated that NF2 and larger tumor size (greater than the median) correlated with poorer local control, but prior surgical resection did not. Serviceable hearing was preserved in 60.0% of SRS patients, 63.2% of HypoFSRT patients, and 44.4% of ConFSRT patients (p = 0.6). Similarly, there were no significant differences in 5-year rates of trigeminal toxicity facial nerve toxicity, vestibular dysfunction, or tinnitus.

CONCLUSIONS

Equivalent 5-year PFR and toxicity rates are shown for patients with vestibular schwanoma selected for SRS, HypoFSRT, and ConFSRT after multidisciplinary evaluation. Factors correlating with tumor progression included NF2 and larger tumor size.

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.

Fractionated stereotactic radiotherapy for acoustic neuromas: a prospective monocenter study of about 158 cases

PURPOSE

To evaluate long-term outcomes and efficacy of fractionated stereotactic radiotherapy in the treatment of acoustic neuromas.

MATERIAL AND METHODS

Between January 1996 and December 2009, 158 acoustic neuromas were treated by FSR in 155 patients. They received a dose of 50.4 Gy, with a safety margin of 1-2mm with a median tumor volume at 2.45 mL (range: 0.17-12.5 mL) and a median follow-up duration at 60 months (range: 24-192).

RESULTS

FSR was well tolerated in all patients with mild sequelae consisting in radiation-induced trigeminal nerve impairments (3.2%), Grade 2 facial neuropathies (2.5%), new or aggravated tinnitus (2.1%) and VP shunting (2.5%). The treatment failed in four patients (2.5%) who had subsequent surgery respectively at 20, 38, 45 and 84 months post-FSR. The local tumor control rates were respectively 99.3%, 97.5% and 95.2% at 3, 5 and >7-year of follow-up. For initial Gardner-Robertson Grade 1 and 2 ANs, the preservation of useful hearing was possible in 54% of the cases; only Grade 1 ANs had stabilized during the course of the follow-up with 71% >7 years. However, hearing preservation was not correlated to the initial Koos Stage and to the radiation dose delivered to the cochlea. Tinnitus (70%), vertigo (59%), imbalance (46%) and ear mastoid pain (43%) had greatly improved post-FRS in most patients. Tumor control, hearing preservation and FRS toxicity were quite similar in patients with NF2, cystic acoustic neuroma, prior surgical resection and Koos Stage 4 AN. No secondary tumors were observed.

CONCLUSION

FSR is a safe and effective therapeutic for acoustic neuromas and could be an alternative to microsurgery. Compared to radiosurgery, there are no contraindications for fractioned doses of stereotactic radiotherapy especially for Stage-4 tumors and patients at high risk of hearing loss.

Radiation therapy and radiosurgery for vestibular schwannomas: indications, techniques, and results

This article describes in detail the uses of and distinctions between stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) for vestibular schwannoma (VS). The authors discuss devices and techniques used in SRS and SRT and, additionally, present readers the approach used by surgeons at Mayo Clinic. They discuss indications and results for both approaches in patients with vestibular schwannoma. Treatment of small and large tumors is discussed, along with cystic tumors and NF2-associated VS. Repeating SRS for vestibular schwannoma is also mentioned.

[Stereotactic radiotherapy of intracranial benign tumors]

Stereotactic radiotherapy can be delivered in one fraction or in multiple fractions schedule. It is used in benign tumours such as meningiomas, mainly localized in the base of the skull, for acoustic schwannoma and pituitary tumours. Whatever the tumour, results with the Gamma Knife(®) are the most numerous, but those obtained by linear accelerators, adapted or dedicated, are comparable. The peripheral dose is preferred to the dose delivered to the isocentre. One fraction stereotactic irradiation should be proposed in small lesions and fractionated treatment for tumours larger. Whatever the tumour, the results are satisfactory with a control rate of 90%. However, this value reflects a disparity assessment, radiological stability for meningiomas, radiological stability and preservation of useful hearing in schwannoma and radiological stability and a decrease in hormonal secretions for pituitary adenomas. Overall complication rates are low. In total, the treatment of benign lesions with stereotactic irradiation gives satisfactory results with few complications.

Stereotactic Radiotherapy for Trigeminal Schwannomas

BACKGROUND:

Data on radiotherapy for trigeminal schwannomas (TSs) and comparison of stereotactic radiosurgery (SRS) with fractionated stereotactic radiotherapy (FSRT) are limited.

OBJECTIVE:

We present a large retrospective review of our institutional experience treating TSs with SRS and FSRT. We also describe a flare phenomenon experienced by some patients.

METHODS:

The records of 23 consecutive TSs patients treated with radiotherapy between 1996 and 2011 were reviewed. We investigated radiographic response, tumor control, and toxicity.

RESULTS:

Ten patients underwent SRS and 13 underwent FSRT, with median clinical follow-up of 32 months (range, 3–120 months). Tumor control at 5 and 10 years was 94% overall. Symptom control at 5 years was achieved in 48% of all patients, with nonsignificant improvement in more patients in the FSRT group than those in the SRS group (56% vs 40%, P = .37). Acute toxicity was higher in the FSRT group (38.5 vs 0%, P &lt; .01), although lesions treated with FSRT were larger (mean, 9.5 mL vs 4.8 mL, P &lt; .01). A symptomatic flare phenomenon occurred in 2 patients (8.7% overall) during FSRT, involving transient cystic formation and dramatic size increase. One lesion regressed in size and 1 remained stable on follow-up.

CONCLUSION:

Tumor control rates for TSs are excellent with SRS and FSRT with minimal toxicity. This represents the first documented report of a flare phenomenon after FSRT for TS treatment. Flare risk after FSRT in previously resected large lesions should be discussed with patients before treatment, and prophylactic oral steroids may be considered.

[Role of radiosurgery and stereotactic radiotherapy in the management of vestibular schwannomas]

PURPOSE OF THE STUDY

In order to investigate the role of radiosurgery and stereotactic radiotherapy in the management of vestibular schwannomas, we have reviewed our own prospective cohort and the main series of the modern literature.

PATIENTS AND METHODS

Between July 14th 1992 and June 1st 2011, 2991 vestibular schwannomas were operated on the Stereotactic and Functional Neurosurgery Department of Timone University Hospital. All the patients have been evaluated prospectively, with a follow up longer than 3 years for 2336 patients, excluding patients suffering from type 2 neurofibromatosis (148 patients). In 7% of the patients, the vestibular schwannoma had previously been resected. According to Koos classification, in 17.6% of the patients, vestibular schwannomas were stage I, 51.8% stage II, 27% stage III and 3.6% stage IV. The mean tumour volume was 2.63 cm(3). According to Garner Robertson classification, the hearing was still functional at the time of radiosurgery in 46% and subnormal in 20.9% of the patients.

RESULTS

Long term tumour control was achieved in 97.5% of the patients. A transient facial palsy was observed in 0.5% of the cases. The rate of trigeminal injury was 0.5%. Useful hearing was preserved at 3 years in 78%. This rate reached 95% in patients with no past history of sudden hearing loss. Other predictors of functional hearing preservation are the young age, the small size of the lesion and a dose to the modiulus of the cochlea lower than 4Gy. We observed no radio-induced tumour. Only large, Koos IV vestibular schwannomas are contraindicated for upfront radiosurgery. In these patients, we propose a combined approach with a deliberately partial microsurgical removal, followed by a radiosurgery of the residue.

CONCLUSION

This cohort is unique by the size of the population and the length of the follow up and results demonstrate the efficacy of radiosurgery and its safety, especially its high rate of hearing preservation.

Multisession stereotactic radiosurgery for vestibular schwannomas: single-institution experience with 383 cases

BACKGROUND

Single-session stereotactic radiosurgery (SRS) treatment of vestibular schwannomas results in excellent tumor control. It is not known whether functional outcomes can be improved by fractionating the treatment over multiple sessions.

OBJECTIVE

To examine tumor control and complication rates after multisession SRS.

METHODS

Three hundred eighty-three patients treated with SRS from 1999 to 2007 at Stanford University Medical Center were retrospectively reviewed. Ninety percent were treated with 18 Gy in 3 sessions, targeting a median tumor volume of 1.1 cm3 (range, 0.02-19.8 cm3).

RESULTS

During a median follow-up duration of 3.6 years (range, 1-10 years), 10 tumors required additional treatment, resulting in 3- and 5-year Kaplan-Meier tumor control rates of 99% and 96%, respectively. Five-year tumor control rate was 98% for tumors < 3.4 cm3. Neurofibromatosis type 2-associated tumors were associated with worse tumor control (P = .02). Of the 200 evaluable patients with pre-SRS serviceable hearing (Gardner-Robertson grade 1 and 2), the crude rate of serviceable hearing preservation was 76%. Smaller tumor volume was associated with hearing preservation (P = .001). There was no case of post-SRS facial weakness. Eight patients (2%) developed trigeminal dysfunction, half of which was transient.

CONCLUSION

Multisession SRS treatment of vestibular schwannomas results in an excellent rate of tumor control. The hearing, trigeminal nerve, and facial nerve function preservation rates reported here are promising.

Gamma knife radiosurgery for vestibular schwannomas: tumor control and functional preservation in 70 patients

OBJECTIVE

We present the previously unreported outcomes of 70 patients treated with Gamma knife radiosurgery for vestibular schwannoma (VS), including comprehensive analysis of clinical outcomes and the effects of lower marginal doses.

METHODS

We performed a retrospective study of patients treated for VS at Gamma knife of Spokane between 2003 and 2008. Endpoints measured include tumor control, hearing preservation, and facial nerve preservation, including the effect of tumor size and marginal dose. Statistical analysis was performed with Wilcoxon signed-rank test, paired Student t test, Mann-Whitney U test, Kendall's rank correlation, Fisher exact test, and Liddell's exact χ(2) test for matched pairs.

RESULTS

With a mean follow-up of 26 months, 93.8% of tumors either shrank or remained static after receiving a mean marginal dose of 12.7 Gy. Tumor control was independent of marginal dose or tumor size. Hearing preservation was achieved in 64% of patients with serviceable function before the treatment. Hearing changes were independent of dose or tumor size. Preservation of good facial nerve function was achieved in 95% of patients. Post-treatment hydrocephalus occurred in 4.4% of patients, but no other significant morbidities were elucidated.

CONCLUSIONS

In the treatment of VS, contemporary radiosurgical techniques and the use of marginal doses below 13 Gy offer excellent tumor control, at high rates relative to surgical intervention. These findings are independent of marginal dose and tumor size. Patients should be informed about the benefits and risks of radiosurgery and microsurgery before choosing an intervention. Further analysis of post-treatment outcomes should be encouraged as follow-up times increase and the treatment protocols continue to evolve.

Clinical outcome after hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors

OBJECTIVE

Surgical resection of skull base tumors can be associated with significant morbidity. In cases where the risks outweigh the benefits, radiation therapy can offer an alternative means to effectively control tumor growth. However, the optimal dose regime for radiation therapy remains controversial. The objective of this study was to assess the neurological outcome, local control rate and morbidity associated with a 5-fraction regime of hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors.

METHODS

Twenty-six patients presenting with two of the most prevalent benign skull base tumors were included in the study. The tumors comprised 16 meningiomas and 10 acoustic neuromas. All patients exhibited preserved cranial nerve function prior to treatment, and a detailed audiological assessment was performed pre- and post-treatment for those patients with acoustic neuroma. Stereotactic radiosurgery was administered with the frameless CyberKnife Robotic Radiosurgery System. In each case, a 5-fraction HSRT regime was used: a dose of 5 Gy × 5 = 25 Gy to 6 Gy × 5 = 30 Gy was prescribed for skull base meningiomas, and 5 Gy × 5 = 25 Gy was prescribed for acoustic neuromas.

RESULTS

The clinical and radiographic median follow-up was 22 months (range: 6-54 months). Radiological assessment showed local control in all 26 tumors (100%), and in 5/26 patients (20%) the tumor showed a decrease in size. Cranial nerve function was preserved in all cases thus far studied; however, 28% of patients had transient Grade II side effects, including fatigue, headaches, unsteadiness and transient subjective worsening of hearing. In two of these patients, the period of transient worsening of hearing was associated with a temporary increase in the size of the tumor on control T2 MR images, consistent with radiation-induced edema. One patient had transient decrease in visual acuity from treatment-related edema. At the last follow-up, 3/16 patients with meningiomas (19%) and 2/10 with acoustic neuromas (20%) showed a decrease in tumor volume and improvement in hearing.

CONCLUSION

A 5-fraction stereotactic radiotherapy regime, as used in this study, seems to be effective for local control of benign skull base tumors in this early follow-up evaluation. Neurological function preservation is excellent with this short regime in the early post-treatment period, but long-term follow-up is crucial for validation.