Fractionated stereotactic radiation therapy and single high-dose radiosurgery for acoustic neuroma: early results of a prospective clinical study

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.

Multisession Radiosurgery for Hearing Preservation

Clinically relevant dose-tolerance limits with reliable estimates of risk in 1-5 fractions for cochlea are still unknown. Timmerman׳s limits from the October 2008 issue of Seminars in Radiation Oncology have served as the basis for clinical practice, augmented by updated constraints in TG-101 and QUANTEC, but the corresponding estimates of risk have not yet been well-reported. A total of 37 acoustic neuroma CyberKnife cases from Medstar Georgetown University Hospital treated in 3 or 5 fractions were combined with single-fraction Gamma Knife data from the 69 cases in Timmer 2009 to form an aggregate dataset of 106 cochlea cases treated in 1-5 fractions. Probit dose-response modeling was performed in the DVH Evaluator software to estimate normal tissue complication probability. QUANTEC recommends keeping single-fraction maximum dose to the cochlea less than 14Gy to maintain less than 25% risk of serviceable hearing loss, and our 17.9% risk estimate for 14Gy in 1 fraction is within their predicted range. In 5 fractions, our estimate of the Timmerman 27.5Gy maximum cochlea dose limit was 17.4%. For cases in which lower risk is required, the Timmerman 12Gy in 1 fraction and the TG-101 limit of 25Gy in 5 fractions had an estimated risk level of 11.8% and 13.8%, respectively. High-risk and low-risk dose tolerance with risk estimates in 1-5 fractions are all presented.

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.

A comprehensive analysis of hearing preservation after radiosurgery for vestibular schwannoma

Object

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

Methods

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

Results

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

Conclusions

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

Outcomes of 75 patients over 12 years treated for acoustic neuromas with linear accelerator-based radiosurgery

The aim of this study was to investigate the efficacy of linear accelerator (LINAC)-based radiosurgery in the treatment of acoustic neuromas. In this retrospective study, we enrolled 75 patients with non-neurofibromatosis type 2 acoustic neuromas who were followed-up for more than 5years. The 75 patients were divided into 3 groups: patients with a newly diagnosed tumor; those with a residual tumor; and those with a recurrent tumor. The average follow-up period was 97.8months. The overall tumor progression-free rate was 92%, and corresponding rates among those with newly diagnosed tumors was 100%, residual tumors was 84.4%, and recurrent tumors was 92.8% (p=0.028). Lesion localization using CT scans correlated with a higher tendency for tumor progression than lesion localization using CT-MRI fusion images (15.6% versus 2.4%, respectively). Residual tumors treated with radiosurgery have a higher progression rate, and careful lesion localization using CT-MRI image fusion is required.

Differences in clinical results after LINAC-based single-dose radiosurgery versus fractionated stereotactic radiotherapy for patients with vestibular schwannomas

PURPOSE

To evaluate the outcomes of patients with vestibular schwannoma (VS) treated with fractionated stereotactic radiotherapy (FSRT) vs. those treated with stereotactic radiosurgery (SRS).

METHODS AND MATERIALS

This study is based on an analysis of 200 patients with 202 VSs treated with FSRT (n = 172) or SRS (n = 30). Patients with tumor progression and/or progression of clinical symptoms were selected for treatment. In 165 out of 202 VSs (82%), RT was performed as the primary treatment for VS, and for 37 VSs (18%), RT was conducted for tumor progression after neurosurgical intervention. For patients receiving FSRT, a median total dose of 57.6 Gy was prescribed, with a median fractionation of 5 x 1.8 Gy per week. For patients who underwent SRS, a median single dose of 13 Gy was prescribed to the 80% isodose.

RESULTS

FSRT and SRS were well tolerated. Median follow-up time was 75 months. Local control was not statistically different for both groups. The probability of maintaining the pretreatment hearing level after SRS with doses of < or =13 Gy was comparable to that of FSRT. The radiation dose for the SRS group (< or =13 Gy vs. >13 Gy) significantly influenced hearing preservation rates (p = 0.03). In the group of patients treated with SRS doses of < or =13 Gy, cranial nerve toxicity was comparable to that of the FSRT group.

CONCLUSIONS

FSRT and SRS are both safe and effective alternatives for the treatment of VS. Local control rates are comparable in both groups. SRS with doses of < or =13 Gy is a safe alternative to FSRT. While FSRT can be applied safely for the treatment of VSs of all sizes, SRS should be reserved for smaller lesions.

Non-audiofacial morbidity after Gamma Knife surgery for vestibular schwannoma

OBJECT

While many studies have been published outlining morbidity following radiosurgical treatment of vestibular schwannomas, significant interpractitioner and institutional variability still exists. For this reason, the authors conducted a systematic review of the literature for non-audiofacial-related morbidity after the treatment of vestibular schwannoma with radiosurgery.

METHODS

The authors performed a comprehensive search of the English-language literature to identify studies that published outcome data of patients undergoing radiosurgery treatment for vestibular schwannomas. In total, 254 articles were found that described more than 50,000 patients and were analyzed for satisfying the authors' inclusion criteria. Patients from these studies were then separated into 2 cohorts based on the marginal dose of radiation: < or = 13 Gy and > 13 Gy. All tumors included in this study were < 25 mm in their largest diameter.

RESULTS

A total of 63 articles met the criteria of the established search protocol, which combined for a total of 5631 patients. Patients receiving > 13 Gy were significantly more likely to develop trigeminal nerve neuropathy than those receiving < 13 Gy (p < 0.001). While we found no relationship between radiation dose and the rate of developing hydrocephalus (0.6% for both cohorts), patients with hydrocephalus who received doses > 13 Gy appeared to have a higher rate of symptomatic hydrocephalus requiring shunt treatment (96% [> 13 Gy] vs 56% [< or = 13 Gy], p < 0.001). The rates of vertigo or balance disturbance (1.1% [> 13 Gy] vs 1.8% [< or = 13 Gy], p = 0.001) and tinnitus (0.1% [> 13 Gy] vs 0.7% [< or = 13 Gy], p = 0.001) were significantly higher in the lower dose cohort than those in the higher dose cohort.

CONCLUSIONS

The results of our review of the literature provide a systematic summary of the published rates of nonaudiofacial morbidity following radiosurgery for vestibular schwannoma.

STEREOTACTIC RADIOSURGERY AND FRACTIONATED STEREOTACTIC RADIOTHERAPY FOR THE TREATMENT OF NONACOUSTIC CRANIAL NERVE SCHWANNOMAS

OBJECTIVE

To review outcomes after fractionated stereotactic radiotherapy (FSR) and stereotactic radiosurgery (SRS) for nonacoustic cranial nerve schwannomas.

METHODS

We reviewed medical records of 39 patients who received FSR or SRS for nonacoustic cranial nerve schwannomas at our institution during the period from 1996 to 2007.

RESULTS

Tumors involved Cranial Nerves V (n = 19), III (n = 2), VI (n = 3), VII (n = 5), IX (n = 2), X (n = 5), and XII (n = 2) and the cavernous sinus (n = 1). Irradiation was performed after partial resection, biopsy, or no previous surgery in 16, 2, and 21 patients, respectively. Twenty-four patients received FSR, delivered in 1.8- to 2.0-Gy fractions to a median dose of 50.4 Gy (range, 45.0–54.0 Gy). Fifteen patients received SRS to a median dose of 12.0 Gy (range, 12–15 Gy). Mild acute toxicity occurred in 23% of the patients. The 2-year actuarial tumor control rate after FSR and SRS was 95%. The median follow-up period was 24 months. Changes in cranial nerve deficits after stereotactic irradiation were analyzed for patients with follow-up periods greater than 12 months (n = 26); cranial nerve deficits improved in 50%, were stable in 46%, and worsened in 4% of the patients. No significant difference was observed for FSR compared with SRS with regard to local control or to improvement of cranial nerve-related symptoms (P = 0.17).

CONCLUSION

SRS and FSR are both well-tolerated treatments for nonacoustic cranial nerve schwannomas, providing excellent tumor control and a high likelihood of symptomatic improvement.

LINEAR ACCELERATOR-BASED STEREOTACTIC RADIOSURGERY FOR BILATERAL VESTIBULAR SCHWANNOMAS IN PATIENTS WITH NEUROFIBROMATOSIS TYPE 2

OBJECTIVE

Patients with neurofibromatosis Type 2 (NF2) patients typically have bilateral vestibular schwannomas (VS) and are at risk for developing bilateral deafness, bilateral trigeminal, and bilateral facial nerve function loss. Previous reports suggested that treatment outcomes in these patients are worse compared with those for patients with sporadic solitary VS. Very few reports, however, have been published on linear accelerator-based radiosurgery (RS) and stereotactic radiation therapy (SRT) in patients with NF2. In particular, in patients with NF2 who already have unilateral hearing loss, avoidance of hearing loss on the opposite side poses a challenge for RS and SRT. We studied our treatment results in patients with NF2 with bilateral VS, treated with linear accelerator-based RS and SRT.

METHODS

In 204 patients with VS treated with RS or SRT in Amsterdam starting from 1992, we identified 25 patients with NF2 who had bilateral tumors. Indications for treatment were either tumor progression on sequential magnetic resonance imaging scans and/or progressive hearing loss. Mean tumor diameter was 2.5 cm. Stereotactic irradiation was administered to all patients using five noncoplanar arcs with a single isocenter to a dose of 10 to 12.5 Gy in a single fraction or 20 to 25 Gy in five fractions in 1 week prescribed to the 80% isodose encompassing the tumor. On the untreated side, all patients showed hearing loss and eight (32%) had ipsilateral deafness. Five patients were followed for less than 1 year. Of the remaining 20 patients, five had ipsilateral deafness before treatment. Consequently, 15 patients were at risk for treatment-related hearing loss. They showed a mean pure tone average (PTA) of 51 dB (8–112 dB) before treatment. After treatment all patients were assessed at yearly intervals including magnetic resonance imaging and pure tone audiometry.

RESULTS

Median follow-up time was 51 months (12–109 mo). Local tumor control was obtained in all 20 patients, and no treatment-related trigeminal or facial nerve toxicity was observed. Hearing status was assessed yearly after treatment. This assessment revealed that the mean PTA in the 15 hearing patients dropped from 51 to 77 dB (40–120 dB). In six patients (40%) the additional PTA loss ranged from 0 to 15 dB, in another six (40%) it ranged from 15 to 45 dB, and in three of these patients (20%), it was more than 45 dB. No additional hearing loss was observed beyond 36 months after treatment.

CONCLUSION

In this largest series in the literature of linear accelerator-based RS and SRT for VS NF2 patients, excellent local control rates were found with minimal facial and trigeminal nerve toxicity. Although more than 40% of the patients retained their hearing level or lost less than 15 dB of PTA on the irradiated side, preservation of hearing remains a major concern.

Tumor-volume changes after radiosurgery for vestibular schwannoma: implications for follow-up MR imaging protocol

BACKGROUND AND PURPOSE

The outcome of radiosurgery for vestibular schwannoma (VS) is assessed by posttreatment measurement of tumor size and could be influenced by the timing and quality of the assessment. This study evaluates the volumetric changes of VS after radiosurgery and proposes a radiologic follow-up program.

MATERIALS AND METHODS

Of 142 patients with VS treated with radiosurgery, we selected patients who were followed at least 3 times during a minimum of 32 months with a T1-weighted gadolinium-enhanced high-resolution 3D MR imaging examination identical to the pretreatment MR imaging. Forty-five patients were identified with a mean follow-up of 50 months (range, 32-78 months). Pre- and posttreatment tumor volumes were calculated by using BrainSCAN software by manually contouring tumors on each MR imaging study. Volume changes of >13% were defined as events.

RESULTS

At last follow-up MR imaging, volumes were smaller in 37 (82.2%) of the 45 patients. Eleven (29.7%) of these 37 tumors showed transient swelling preceding regression, with a median time to regression of 34 months (range, 20-55 months). Seven (15.6%) of the 45 tumors had volume progression compared with the tumor on pretreatment MR imaging studies. Of these 7 tumors, 3, however, had volume regression compared with the preceding MR imaging study, and in 4, volume progression was ongoing. One tumor remained the same.

CONCLUSIONS

Tumor-volume measurements by standardized T1-weighted gadolinium-enhanced high-resolution 3D MR imaging follow-up protocols revealed good local control of VS after radiosurgery. The first-follow-up MR imaging at 2 years and the second at 5 years postradiosurgery differentiated transient progression from ongoing progression and may prevent unnecessary therapeutic interventions.

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.

Long-term outcome of stereotactic radiosurgery (SRS) in patients with acoustic neuromas

PURPOSE

To evaluate the effectiveness and long-term outcome of stereotactic radiosurgery (SRS) for acoustic neuromas (AN).

PATIENTS AND METHODS

Between 1990 and 2001, we treated 26 patients with 27 AN with SRS. Two patients suffered from neurofibromatosis type 2. Before SRS, a subtotal or total resection had been performed in 3 and in 5 patients, respectively. For SRS, a median single dose of 13 Gy/80% isodose was applied.

RESULTS

The overall actuarial 5-year and 10-year tumor control probability in all patients was 91%. Two patients developed tumor progression after SRS at 36 and 48 months. Nineteen patients (73%) were at risk of treatment-related facial nerve toxicity; of these, 1 patient developed a complete facial nerve palsy after SRS (5%). A total of 93% of the lesions treated were at risk of radiation-induced trigeminal neuralgia. Two patients (8%) developed mild dysesthesia of the trigeminal nerve after SRS. The hearing preservation rate in patients with useful hearing before SRS was 55% at 9 years.

CONCLUSION

Stereotactic radiosurgery results in good local control rates of AN and the risk of cranial nerve toxicities is acceptable. As toxicity is lower with fractionated stereotactic radiotherapy, SRS should be reserved for smaller lesions.

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.

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.

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.

Management of vestibular schwannoma by fractionated stereotactic radiotherapy and associated cerebrospinal fluid malabsorption

OBJECT

The goal of this study was to investigate outcomes in patients with vestibular schwannoma (VS) who were treated with fractionated stereotactic radiotherapy (SRT).

METHODS

One hundred one patients with VS were treated with fractionated SRT at a radiation level of 40 to 50 Gy administered in 20 to 25 fractions over a 5- to 6-week period. The median tumor size in these patients was 19 mm (range 3-40 mm), and 27 tumors were larger than 25 mm. Patients were consistently followed up using magnetic resonance imaging every 6 months for 5 years in principle. The median follow-up period was 45 months. The actuarial 5-year rate of tumor control (no growth > 2 mm and no requirement for salvage surgery) was 91.4% (95% confidence interval 85.2-97.6%). Three patients with progressive tumors underwent salvage tumor resection. The actuarial 5-year rate of useful hearing preservation (Gardner-Robertson Class I or II) was 71%. The observed complications of fractionated SRT included transient facial nerve palsy (4% of patients), trigeminal neuropathy (14% of patients), and balance disturbance (17% of patients). No new permanent facial weakness occurred after fractionated SRT. Eleven patients (11%) who had progressive communicating hydrocephalus (cerebrospinal fluid malabsorption) and no evidence of tumor growth after fractionated SRT required a shunt. The symptoms of this type of hydrocephalus were similar to those of normal-pressure hydrocephalus and occurred 4 to 20 months (median 12 months) after fractionated SRT. The mean size (+/- standard deviation) of tumors causing symptomatic hydrocephalus (25.5 +/- 7.8 mm) was significantly larger than that of other tumors (18.2 +/- 8.7 mm) (p = 0.011). Only four of the 72 patients with tumors smaller than 25 mm in maximum diameter received a shunt.

CONCLUSIONS

Fractionated SRT resulted in an excellent tumor control rate, even for relatively large tumors, and produced a high rate of hearing preservation that was comparable to the best results of single-fraction radiosurgery. The progression of communicating hydrocephalus should be monitored closely, particularly in patients harboring a large VS.

The linear-quadratic model and fractionated stereotactic radiotherapy

PURPOSE

To determine the dose per fraction that could be used when gamma knife or linear accelerator-based stereotactic treatments are delivered in 2 or more fractions.

METHODS AND MATERIALS

The linear-quadratic (LQ) model was used to calculate the dose per fraction for a multiple-fraction regimen which is biologically equivalent to a given single-fraction treatment. The results are summarized in lookup tables.

RESULTS AND CONCLUSION

The tables can be used by practicing clinicians as a guide in planning fractionated treatment. For the large doses used in typical stereotactic treatments and for small fraction numbers, the model is not very sensitive to the value of the alpha/beta ratio in the LQ model. A simple rule of thumb is found that for two-fraction and three-fraction treatments the dose per fraction is roughly two-thirds and one-half of the single-fraction treatment dose, respectively.

Proton beam radiosurgery for vestibular schwannoma: tumor control and cranial nerve toxicity

OBJECTIVE

We sought to determine the tumor control rate and cranial nerve function outcomes in patients with vestibular schwannomas who were treated with proton beam stereotactic radiosurgery.

METHODS

Between November 1992 and August 2000, 88 patients with vestibular schwannomas were treated at the Harvard Cyclotron Laboratory with proton beam stereotactic radiosurgery in which two to four convergent fixed beams of 160-MeV protons were applied. The median transverse diameter was 16 mm (range, 2.5-35 mm), and the median tumor volume was 1.4 cm(3) (range, 0.1-15.9 cm(3)). Surgical resection had been performed previously in 15 patients (17%). Facial nerve function (House-Brackmann Grade 1) and trigeminal nerve function were normal in 79 patients (89.8%). Eight patients (9%) had good or excellent hearing (Gardner-Robertson [GR] Grade 1), and 13 patients (15%) had serviceable hearing (GR Grade 2). A median dose of 12 cobalt Gray equivalents (range, 10-18 cobalt Gray equivalents) was prescribed to the 70 to 108% isodose lines (median, 70%). The median follow-up period was 38.7 months (range, 12-102.6 mo).

RESULTS

The actuarial 2- and 5-year tumor control rates were 95.3% (95% confidence interval [CI], 90.9-99.9%) and 93.6% (95% CI, 88.3-99.3%). Salvage radiosurgery was performed in one patient 32.5 months after treatment, and a craniotomy was required 19.1 months after treatment in another patient with hemorrhage in the vicinity of a stable tumor. Three patients (3.4%) underwent shunting for hydrocephalus, and a subsequent partial resection was performed in one of these patients. The actuarial 5-year cumulative radiological reduction rate was 94.7% (95% CI, 81.2-98.3%). Of the 21 patients (24%) with functional hearing (GR Grade 1 or 2), 7 (33.3%) retained serviceable hearing ability (GR Grade 2). Actuarial 5-year normal facial and trigeminal nerve function preservation rates were 91.1% (95% CI, 85-97.6%) and 89.4% (95% CI, 82-96.7%). Univariate analysis revealed that prescribed dose (P = 0.005), maximum dose (P = 0.006), and the inhomogeneity coefficient (P = 0.03) were associated with a significant risk of long-term facial neuropathy. No other cranial nerve deficits or cancer relapses were observed.

CONCLUSION

Proton beam stereotactic radiosurgery has been shown to be an effective means of tumor control. A high radiological response rate was observed. Excellent facial and trigeminal nerve function preservation rates were achieved. A reduced prescribed dose is associated with a significant decrease in facial neuropathy.

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.

Radiosurgery for acoustic neuromas: results of low-dose treatment

OBJECTIVE

The results of radiosurgical treatment of acoustic neuromas have improved by reducing the tumor marginal doses. We report relatively long-term follow-up results (>5 yr) for patients who underwent low-dose radiosurgery.

METHODS

We treated and followed 51 consecutive patients with unilateral acoustic neuromas who were treated from January 1994 to December 1996 by gamma knife radiosurgery at low doses (</=12 Gy to the tumor margin). The average age of the patients was 55 years (range, 32-76 yr). The treatment volume was 0.7 to 24.9 cm(3) (median, 3.6 cm(3)). The marginal radiation dose was 8 to 12 Gy (median, 12 Gy), and the follow-up period ranged from 18 to 96 months (median, 60 mo).

RESULTS

Clinical tumor growth control (without tumor resection) was achieved in 96% of patients, and the 5-year tumor growth control rate was 92%. Hearing was preserved in 59% of those with preradiosurgical hearing preservation (Gardner-Robertson Classes 1-4), and improvements (>20 dB of improvement) were noted in 9% of the patients with any hearing. Hearing was preserved at a useful level (Gardner-Robertson Classes 1 and 2) in 56% of patients. Although preexisting trigeminal neuropathy worsened in 4% of the patients, our patients did not experience new facial palsies or trigeminal neuropathies after radiosurgery. Facial spasm occurred in 6% of the patients, and intratumoral bleeding occurred in 4% of patients.

CONCLUSION

Low-dose radiosurgery (</=12 Gy at the tumor margin) can achieve a high tumor growth control rate and maintain low postradiosurgical morbidity (including hearing preservation) for acoustic neuromas.

Stereotactic radiosurgery for benign neoplasms

Over the last decade, the use of stereotactic radiosurgery (SRS) for the treatment of intracranial lesions has grown significantly. In addition to malignant brain tumors and vascular malformations, benign tumors have also been treated with SRS. Although surgical resection has long been considered the gold standard in the management of such benign lesions, the outcomes of SRS in various benign neoplasms appears to be comparable. In this review, we will examine the literature as it pertains to the treatment of benign brain tumors with SRS. Of particular note, we will examine the results of SRS in acoustic neuromas, meningiomas, pituitary adenomas, and other benign tumors.

Gamma knife model C with the automatic positioning system and its impact on the treatment of vestibular schwannomas

Object. The aim of this study was to assess the effects of the gamma knife automatic positioning system (APS) on the treatment of patients, particularly effects of this system on the treatment of patients with vestibular schwannomas (VSs), with a view to reducing loss of hearing.

Methods. The dose delivery with an increased number of shots was checked with GAFChromic Film for various numbers of shots (one to 129). The results in the first 549 patients were recorded. In addition a series of 59 patients with VSs treated with 13 Gy to the 65% isodose is presented. The authors have termed this the “13 on 65” concept.

The film dosimetry showed that a large number of small shots did not materially affect the dose and dose distribution produced by gamma knife treatment.

The APS was used alone in 72% of arteriovenous malformations, 71% of meningiomas, 94% of VSs, and 84% of pituitary adenomas. Metastatic tumors were accessible in a pure APS mode in 59% of all cases, glioma in 58%, and uveal melanoma in 10% of the cases. Thus two thirds of patients could be treated using APS alone. It was possible to use the APS and manual systems together for complex or very eccentrically placed targets. The APS resulted in the use of a larger number of isocenters.

After a mean follow-up period of 15 months, the results in patients with the VSs in whom 13 Gy was delivered to the 65% isodose were similar to those in patients treated with the more conventional 50% margin isodose. There was no change in the incidence of hearing loss within the study period, and the incidence of trigeminal and facial neuropathies remained unchanged after treatment as well.

Conclusions. The APS encourages the design of more conformal dose plans. The greater use of smaller collimators results in a steeper dose gradient with a smaller amount of radiation outside the target volume. Because the APS is able to apply a large number of smaller isocenters in an acceptable time, the number of isocenters used is increased. An increased number of isocenters can also be used to reduce the maximum radiation dose and increase the homogeneity in a given dose plan.

Fractionated stereotactic radiotherapy: a short review

Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic radiotherapy. We present in this article a review of the underlying basic physical and radiobiological principles of fractionated stereotactic radiotherapy and review the clinical experience for ateriovenus malformations, pituitary adenomas, mengiomas, vestibular schwanomas, low grade astrocytomas, malignant gliomas, and brain metastases.

Reduced-dose radiosurgery for vestibular schwannomas

OBJECTIVE

To evaluate tumor control and complications associated with low-dose radiosurgery for vestibular schwannomas.

METHODS

Between December 1993 and January 2000, 47 patients with vestibular schwannomas were treated at our center with gamma knife radiosurgery. The marginal tumor doses ranged from 7.5 to 14.0 Gy (median, 12.0 Gy) for patients treated after microsurgery and from 10.0 to 15.0 Gy (median, 12.0 Gy) for patients in whom radiosurgery was the primary treatment. The median maximum tumor diameter was 18 mm (range, 3-50 mm). Evaluation included audiometry, neurological examination, and serial imaging tests. A survey was conducted at the time of analysis.

RESULTS

Follow-up data were available for 45 patients and ranged from 1 to 7 years (median, 3.6 yr). In 43 patients (96%), tumor control (no radiographic progression or surgical resection) was observed. All 33 previously untreated patients had tumor control. Transient facial weakness, experienced in two patients (4%), had resolved completely within 6 months. No patient developed trigeminal neuropathy. Hearing was diminished from baseline in 12% of patients with useful hearing (Gardner-Robertson Class III). However, all patients with pretreatment hearing Gardner-Robertson Class I or II maintained testable hearing (Class I to III) at the most recent examination.

CONCLUSION

Low-dose radiosurgery in this series provided comparable local control and decreased incidences of complications in relation to other reports. Additional follow-up will allow more definitive conclusions to be reached regarding the ultimate rates of tumor control and hearing preservation. Nevertheless, the current dose used for vestibular schwannomas at the University of Maryland Medical Center is 12.0 Gy to the tumor periphery.

Medication for hearing loss after fractionated stereotactic radiotherapy (SRT) for vestibular schwannoma

PURPOSE

To investigate the effectiveness of corticosteroid treatments for patients showing decreases in hearing levels after stereotactic radiotherapy for vestibular schwannoma.

METHODS AND MATERIALS

Twenty-one patients experienced a hearing loss in pure-tone average at greater than 20 dB or less than 10 dB within 1 year after irradiation administration of 44 Gy/22 fractions followed by a 4 Gy boost. Eight received oral prednisone at a daily dose of 30 mg, which was gradually decreased (medicated group), and 13 received none (nonmedicated group). The average observation period was 26.7 +/- 16.6 (range: 6--69) months.

RESULTS

Hearing recovery was seen after initial onset of the hearing loss in all 8 patients in the medicated group and in 2 of 13 patients in the nonmedicated group (p = 0.001). The hearing recovery, that is, the change in pure-tone average (dB) at the last follow-up from the onset of hearing loss, was 9.8 +/- 6.9 dB (recovery) in the medicated group and -9.4 +/- 12.8 dB (further loss) in the nonmedicated group (p = 0.0013). The hearing recovery rate, normalizing to the degree of the hearing loss before medication, was also significantly higher in the medicated group than in the nonmedicated group (p = 0.0014).

CONCLUSIONS

Corticosteroidal intake is suggested to be effective in improving hearing loss after stereotactic radiotherapy, at least in young patients having a useful pretreatment hearing level, if the treatment for hearing loss is administered immediately after the hearing loss is first detected.