Linear accelerator-based stereotactic radiosurgery for acoustic schwannomas

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.

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.

Radiosurgery in patients with bilateral vestibular schwannomas

BACKGROUND

Patients with bilateral vestibular schwannomas offer a unique opportunity to determine the effectiveness of radiosurgery. By using the untreated tumor as an internal control, one can determine whether radiosurgery was able to interrupt the natural history of the treated tumor.

METHODS

From September 1998 to November 2004, 13 patients with neurofibromatosis type 2 had 14 tumors treated with radiosurgery at the University of Florida. A retrospective analysis was performed on these patients. Actuarial statistics were used to analyze local control in both the treated and untreated tumor.

RESULTS

The average follow-up length was 38 months. One patient failed to send a follow-up MRI. Actuarial local control in the treated tumors was 100% at 1 year and 92% at 2 and 5 years. Only 1 of the treated tumors continued to grow. In the untreated tumors, actuarial local control was 100% at 1 year, 78% at 2 years and 21% at 5 years. None of the untreated tumors decreased in size.

CONCLUSION

In all but 1 patient with follow-up data, radiosurgery successfully prevented or reversed tumor growth. Additionally, half of the untreated tumors continued to grow. This study shows that radiosurgery alters the natural history of vestibular schwannomas.

Long-Term Follow-up of Acoustic Schwannoma Radiosurgery With Marginal Tumor Doses of 12 to 13 Gy

PURPOSE

To define long-term tumor control and clinical outcomes of radiosurgery with marginal tumor doses of 12 to 13 Gy for unilateral acoustic schwannoma.

METHODS AND MATERIALS

A total of 216 patients with previously untreated unilateral acoustic schwannoma underwent Gamma Knife radiosurgery between 1992 and 2000 with marginal tumor doses of 12 to 13 Gy (median, 13 Gy). Median follow-up was 5.7 years (maximum, 12 years; 41 patients with >8 years). Treatment volumes were 0.08-37.5 cm(3) (median, 1.3 cm(3)).

RESULTS

The 10-year actuarial resection-free control rate was 98.3% +/- 1.0%. Three patients required tumor resection: 2 for tumor growth and 1 partial resection for an enlarging adjacent subarachnoid cyst. Among 121 hearing patients with >3 years of follow-up, crude hearing preservation rates were 71% for keeping the same Gardner-Robertson hearing level, 74% for serviceable hearing, and 95% for any testable hearing. For 25 of these patients with intracanalicular tumors, the respective rates for preserving the same Gardner-Robertson level, serviceable hearing, and testable hearing were 80%, 88%, and 96%. Ten-year actuarial rates for preserving the same Gardner-Robertson hearing levels, serviceable hearing, any testable hearing, and unchanged facial and trigeminal nerve function were 44.0% +/- 11.7%, 44.5% +/- 10.5%, 85.3% +/- 6.2%, 100%, and 94.9% +/- 1.8%, respectively.

CONCLUSIONS

Acoustic schwannoma radiosurgery with 12 to 13 Gy provides high rates of long-term tumor control and cranial nerve preservation after long-term follow-up.

Long-term follow-up reveals low toxicity of radiosurgery for vestibular schwannoma

AIM

The long-term effects of radiosurgery of vestibular schwannomas were investigated in a group of consecutively treated patients.

METHODS AND MATERIALS

Between 1995 and 2001, 26 patients (median age: 67, range: 30-82) with a vestibular schwannoma were treated by Linac-based stereotactic radiosurgery (SRS). The median follow-up was 49 months (16-85 months). Only progressive tumours were treated. The median size of tumours was 18 mm (range 9-30 mm). Before SRS, 11 patients had a useful hearing (Gardner-Robertson classes 1 and 2). Single doses of 10-14 Gy were prescribed at the 80% isodose at the tumour margin. The follow-up consisted of regular imaging with MRI the first 3-6 months after the intervention, followed by additional yearly MRIs, a hearing test and a neurological examination.

RESULT

The 5-year-probability of tumour control (defined as stabilization or decrease in size) was 95%. Five-year-probability of preservation of hearing and facial nerve function was 96% and 100%, respectively. Hearing was preserved in 10 out of 11 patients who had a normal or useful hearing at the time of treatment. Mild and transient trigeminal toxicity occurred in 2 (8%) patients. It appeared to be significantly correlated to the dose used (p=0.044). However, only a tendency to significance could be demonstrated in the relationship between the two factors when using the Cox analysis (hazard ratio=1.7; 95% CI: 0.7-3.9; p=0.23).

CONCLUSIONS

With the doses used, our study demonstrates that SRS provides an equivalent tumour control rate when compared to surgery, as well as on a long-term basis, an excellent preservation of the facial and the acoustic nerves. Although no permanent trigeminal toxicity was observed, our data confirm that doses below 14 Gy can avoid transient dysesthesias.

Linear accelerator radiosurgery for vestibular schwannoma: measuring tumor volume changes on serial three-dimensional spoiled gradient-echo magnetic resonance images

OBJECT

The authors report on a series of 46 patients harboring vestibular schwannomas (VSs) treated using linear accelerator (LINAC) radiosurgery and an analysis of serial magnetic resonance (MR) imaging data, specifically the changes in tumor volume.

METHODS

Fifty-three consecutive patients underwent LINAC radiosurgery for VS between 1993 and 2002. Seven of these patients were lost to follow up. Three-dimensional (3D) spoiled gradient-echo (SPGR) MR imaging was performed at 3- to 4-month intervals after radiosurgery. Tumor volume was measured on Gd-enhanced MR images of each slice. The median duration of follow-up MR imaging studies was 56.5 months (range 12-120 months). Follow-up imaging studies were conducted for longer than 1 year in 42 of 53 patients. Tumor volume changes were categorized into four types: enlargement (eight lesions [19%]), no change (two lesions [4.8%]), transient enlargement followed by shrinkage (19 lesions [45.2%]), and direct shrinkage (13 lesions [31%]). Two cases (4.8%) with twice the initial tumor volume required repeated radiosurgery. All cases of transient enlargement had subsequent shrinkage within 2 years after radiosurgery. Nine (21.4%) of 42 patients demonstrated ventricular enlargement on MR images obtained after radiosurgery. Three patients (7.1%) required placement of a ventriculoperitoneal shunt because of symptomatic hydrocephalus, and another four cases (9.5%) spontaneously resolved.

CONCLUSIONS

Volume measurement on 3D-SPGR MR imaging was a suitable method to assess tumor changes. Volume changes beyond twofold or continuous enlargement for longer than 2 years after radiosurgery are key criteria in rating the effects of radiation. Some cases of hydrocephalus after radiosurgery resolved spontaneously and their rates of occurrence were similar to the typical incidence of hydrocephalus associated with VS.

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.

Acoustic neuroma radiosurgery with marginal tumor doses of 12 to 13 gy

PURPOSE

To define tumor control and clinical outcomes of radiosurgery to marginal tumor doses of 12-13 Gy for unilateral acoustic neuroma patients.

METHODS AND MATERIALS

Three hundred thirteen patients with previously untreated unilateral acoustic neuromas (vestibular schwannomas) underwent gamma knife radiosurgery between February 1991 and February 2001 with marginal tumor doses of 12-13 Gy (median, 13 Gy). Median follow-up was 24 months (maximum, 115 months; 36 patients with > or =60 months). Maximum doses were 20-26 Gy (median, 26 Gy), and treatment volumes were 0.04-21.4 mL (median, 1.1 mL).

RESULTS

The actuarial 6-year clinical tumor control rate (no requirement for surgical intervention) for the entire series was 98.6 +/- 1.1%. Two patients required tumor resection; one had a complete resection for solid tumor growth and one required partial resection for an enlarging adjacent subarachnoid cyst. Six-year actuarial rates for preservation of facial nerve function, normal trigeminal nerve function, unchanged hearing level, and useful hearing were 100%, 95.6 +/- 1.8%, 70.3 +/- 5.8%, and 78.6 +/- 5.1%, respectively. The risk of developing trigeminal neuropathy correlated with increasing tumor volume (p = 0.038).

CONCLUSIONS

Acoustic neuroma radiosurgery with doses of 12-13 Gy provides high rates of tumor control and cranial nerve preservation.

Results of outpatient gamma knife radiosurgery for primary therapy of acoustic neuromas

Stereotactic radiosurgery (SRS) has been recognized as a non-invasive alternative to surgery for the treatment of acoustic neuromas. Purpose of the current study was to define the impact of outpatient gamma knife radiosurgery (GKS) for patients with unilateral sporadic acoustic neuromas treated within ten years. Follow-up images were analyzed using tumor volume measurements. 219 patients with sporadic acoustic neuromas were treated by GKS as primary therapy. Patients with NF-2 tumors were excluded. Patients were eligible for GKS up to a size limit of 12.5 cm3. The median follow up time was 6 years after radiosurgery. The local tumor control rate was high (97%). Cranial nerve morbidities were comparably low. 10% of the patients developed hearing loss after radiosurgery and one patient experienced a transient facial neuropathy (0.5%). Transient trigeminal neuropathy developed in 12 patients (5%) and was found to be dependent on the tumor size before treatment. Outpatient gamma knife radiosurgery is a safe and effective treatment method for selected patients with sporadic vestibular schwannomas.

Low-dose radiosurgery for benign intracranial lesions

This study assesses the efficacy and neurotoxicity of radiosurgical treatment of benign intracranial tumors using a linear accelerator, with relatively low dose and homogeneous dosimetry. Between June 1998 and July 2000, 27 patients were treated for benign lesions with radiosurgery using a 6-MV linear accelerator-based X-knife system and circular collimators. The lesions included schwannoma, meningioma, papillary cyst adenoma, and hemangioblastoma. Five patients had tissue diagnosis. The mean peripheral dose to the tumor margin was 12.8 Gy. The mean dose to the isocenter was 16.3 Gy. One to five isocenters were used to treat these lesions, with a mean of 10 arcs per isocenter and mean collimator size of 1.25 cm. Follow-up information was available on all patients, with a mean follow-up duration of 33 months. Six patients (22%) had improved symptoms and 21 (78%) had stable symptoms. Eight patients (30%) had regression of tumor and 19 had stable disease (70%). No patient had tumor progression, and Radiation Therapy Oncology Group (RTOG) grade III or IV toxicity did not occur in any patients. In 3 patients (11%), RTOG grade I or grade II neurotoxicity developed. Of these, one patient had worsening of a preexisting VIIth nerve deficit that required temporary oral methylprednisolone, and in two patients a mild trigeminal deficit developed that did not require any medical intervention. Low-dose homogeneous radiosurgery using a linear accelerator is an effective treatment for benign intracranial tumors. If lower, more homogeneous radiation doses produce responses as durable as higher doses, then toxicity might be further reduced.

Linear accelerator–based radiosurgery for vestibular schwannoma

Despite major advances in skull base surgery and microsurgical techniques, surgery for vestibular schwannoma (VS) carries a risk of complications. Some are inherent to general anesthesia and surgery of any type and include myocardial infarction, pneumonia, pulmonary embolism, and infection. Some are specific to neurosurgery in this area of the brain, and include hydrocephalus, cerebrospinal fluid leak, facial nerve paralysis, facial numbness, hearing loss, ataxia, dysphagia, and major stroke. Even in the hands of very experienced acoustic surgeons, these risks cannot be eliminated.

Radiosurgery provides an outpatient, noninvasive alternative for the treatment of small acoustic schwannomas. Initially radiosurgery was undertaken in “high-risk” patients, including the elderly, those with severe medical comorbidities, and those in whom tumors recurred after surgery. Additionally, a high rate of cranial nerve morbidity was reported. With improvements in dosimetry planning and dose selection, however, authors practicing at radiosurgical centers now report very low complication rates, as well as high tumor control rates.

In this report the authors specifically review the results of linear accelerator–based radiosurgery for VS and compare these outcomes with the best surgical alternatives.

Proton beam stereotactic radiosurgery of vestibular schwannomas

PURPOSE

The proton beam's Bragg peak permits highly conformal radiation of skull base tumors. This study, prompted by reports of transient (30% each) and permanent (10% each) facial and trigeminal neuropathy after stereotactic radiosurgery of vestibular schwannomas with marginal doses of 16-20 Gy, assessed whether proton beam radiosurgery using a marginal dose of only 12 Gy could control vestibular schwannomas while causing less neuropathy.

METHODS AND MATERIALS

Sixty-eight patients (mean age 67 years) were treated between 1992 and 1998. The mean tumor volume was 2.49 cm(3). The dose to the tumor margin (70% isodose line) was 12 Gy. The prospectively specified follow-up consisted of neurologic evaluation and MRI at 6, 12, 24, and 36 months.

RESULTS

After a mean clinical follow-up of 44 months and imaging follow-up of 34 months in 64 patients, 35 tumors (54.7%) were smaller and 25 (39.1%) were unchanged (tumor control rate 94%; actuarial control rate 94% at 2 years and 84% at 5 years). Three tumors enlarged: one shrank after repeated radiosurgery, one remained enlarged at the time of unrelated death, and one had not been imaged for 4 years in a patient who remained asymptomatic at last follow-up. Intratumoral hemorrhage into one stable tumor required craniotomy that proved successful. Thus, 97% of tumors required no additional treatment. Three patients (4.7%) underwent shunting for hydrocephalus evident as increased ataxia. Of 6 patients with functional hearing ipsilaterally, 1 improved, 1 was unchanged, and 4 progressively lost hearing. Cranial neuropathies were infrequent: persistent facial hypesthesia (2 new, 1 exacerbated; 4.7%); intermittent facial paresthesias (5 new, 1 exacerbated; 9.4%); persistent facial weakness (2 new, 1 exacerbated; 4.7%) requiring oculoplasty; transient partial facial weakness (5 new, 1 exacerbated; 9.4%), and synkinesis (5 new, 1 exacerbated; 9.4%).

CONCLUSION

Proton beam stereotactic radiosurgery of vestibular schwannomas at the doses used in this study controls tumor growth with relatively few complications.

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

PURPOSE

To evaluate the efficacy and toxicity of fractionated stereotactic radiotherapy (FSRT) for vestibular schwannomas in patients treated at two university-affiliated hospitals.

METHODS AND MATERIALS

Thirty-nine patients were treated between April 1996 and September 2000. The median age was 56 years (range: 29-80), and median maximal tumor diameter was 20 mm (range: 9-40). A total of 11 patients had fifth and/or seventh cranial nerve dysfunction before irradiation; 2 patients had only facial weakness, 5 patients had only facial numbness, and 4 patients had both facial weakness and numbness. Thirty-three patients were treated with primary FSRT, and 6 patients were treated for recurrent or persistent disease after previous surgery. All patients were treated with 6-MV photons using a stereotactic system with a relocatable frame. The 39 patients received 50 Gy in 25 fractions over 5 weeks. Median follow-up was 21.8 months (range: 4.4-49.6).

RESULTS

Local control was achieved in 37 patients (95%). Two patients experienced deterioration of their symptoms at 3 and 20 months as a result of clinical progression in one case and tumor progression in the other and underwent surgery post FSRT. A total of 19/28 (67.9%) patients preserved serviceable hearing after FSRT. Deterioration of the facial and trigeminal nerves was observed in only 2 patients who were treated with surgery post FSRT.

CONCLUSION

FSRT provided excellent tumor control with minimal morbidity and good hearing preservation in this cohort of patients. Longer follow-up is required to confirm long-term control rates.

Radiosurgery for paraganglioma of the temporal bone

PURPOSE

To report the outcome of patients with paraganglioma of the temporal bone treated with stereotactic radiosurgery at the University of Florida.

METHODS AND MATERIALS

Between January 1997 and June 1999, five patients with paraganglioma of the temporal bone were treated with Linac-based stereotactic radiosurgery at the University of Florida. The ages of the three female and two male patients were between 40 and 88 years (median, 49 years). Four patients were treated at initial presentation, and one had recurrent disease. Treatment volumes ranged from 4.9 cm3 to 18.4 cm3, with a mean of 10.84 cm3. The dose applied to the margin of the tumor varied from 12.5 to 15 Gy (median, 15 Gy). The treatment dose was specified to the 80% isodose shell in two cases and to the 70% isodose shell in three cases. The median follow-up time was 27 months, ranging from 14 to 50 months.

RESULTS

One of four previously untreated patients had a relapse at the primary tumor site. Treatment failure occurred at the field margin 6 months after radiosurgery; the patient was subsequently treated with fractionated stereotactic radiotherapy and at the time of analysis had no evidence of disease, 21 months after initiation of salvage therapy. The patient treated at the time of recurrence after conventional radiotherapy had a local recurrence 40 months after radiosurgery. At the time of this recurrence, the patient had biopsy-proven metastatic disease in two cervical lymph nodes, and no salvage therapy was performed. All patients were alive at the time of the analysis, one with disease present. Presenting symptoms improved in two patients and stabilized in one. The two patients who had local recurrence develop had worsening of their symptoms. One patient had a cranial nerve V palsy develop 6 months after treatment, which resolved after a few months.

CONCLUSIONS

In this series, the results with stereotactic radiosurgery are discouraging compared with our results with conventional fractionated radiotherapy in patients with paraganglioma of the temporal bone.

Stereotactic radiosurgery of acoustic tumors

Stereotactic radiotherapy has an inherent disadvantage in that it does not directly reduce tumor volume. In this increasing environment of cost-containment, however, this modality offers several advantages (see box). Some investigators believe that, over the next generation, stereotactic radiotherapy will be the mainstay of vestibular schwannoma care, with microsurgery being the exception and being reserved for patients needing urgent decompression and for very young patients [12]. Increasing numbers of patients are undergoing stereotactic radiotherapy as a matter of preference following the provision of sufficient information on the two treatment procedures. When counseling younger patients, it is important to remember that no long-term data about the control rate for stereotactic radiotherapy with the most recent, lower doses are available. Also, surgical salvage, which is necessary in some patients, produces a poor outcome following radiation therapy. Published reports have demonstrated similar facial nerve, hearing preservation, and tumor control rates in the short term only [32,33]. Data is insufficient to assess the risk for inducing a secondary, treatment-related malignancy. Until long-term results are available, stereotactic radiotherapy should be reserved for medically infirm patients, elderly patients, patients with contralateral deafness or bilateral tumors, and patients who have failed prior microsurgery. Radiotherapy is not the preferred primary treatment modality for vestibular schwannoma based on currently published results.

Radiotherapy and radiosurgery for skull base tumors

Tumors arising in the vicinity of the skull base are relatively uncommon; however, lesions that may be successfully treated by radiotherapy and radiosurgery include temporal bone chemodectomas, schwannomas, juvenile angiofibromas, pituitary adenomas, and meningiomas. This article reviews treatment techniques and results and discusses the pertinent literature.

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.

Stereotactic radiosurgery and fractionated stereotactic radiotherapy for the treatment of acoustic schwannomas: comparative observations of 125 patients treated at one institution

BACKGROUND

Stereotactic radiosurgery (SRS) and, more recently, fractionated stereotactic radiotherapy (SRT) have been recognized as noninvasive alternatives to surgery for the treatment of acoustic schwannomas. We review our experience of acoustic tumor treatments at one institution using a gamma knife for SRS and the first commercial world installation of a dedicated linac for SRT.

METHODS

Patients were treated with SRS on the gamma knife or SRT on the linac from October 1994 through August 2000. Gamma knife technique involved a fixed-frame multiple shot/high conformality single treatment, whereas linac technique involved daily conventional fraction treatments involving a relocatable frame, fewer isocenters, and high conformality established by noncoplanar arc beam shaping and differential beam weighting.

RESULTS

Sixty-nine patients were treated on the gamma knife, and 56 patients were treated on the linac, with 1 NF-2 patient common to both units. Three patients were lost to follow-up, and in the remaining 122 patients, mean follow-up was 119 +/- 67 weeks for SRS patients and 115 +/- 96 weeks for SRT patients. Tumor control rates were high (> or =97%) for sporadic tumors in both groups but lower for NF-2 tumors in the SRT group. Cranial nerve morbidities were comparably low in both groups, with the exception of functional hearing preservation, which was 2.5-fold higher in patients who received conventional fraction SRT.

CONCLUSION

SRS and SRT represent comparable noninvasive treatments for acoustic schwannomas in both sporadic and NF-2 patient groups. At 1-year follow-up, a significantly higher rate of serviceable hearing preservation was achieved in SRT sporadic tumor patients and may therefore be preferable to alternatives including surgery, SRS, or possibly observation in patients with serviceable hearing.

Results of acoustic neuroma radiosurgery: an analysis of 5 years' experience using current methods

OBJECT

The goal of this study was to define tumor control and complications of radiosurgery encountered using current treatment methods for the initial management of patients with unilateral acoustic neuroma.

METHODS

One hundred ninety patients with previously untreated unilateral acoustic neuromas (vestibular schwannomas) underwent gamma knife radiosurgery between 1992 and 1997. The median follow-up period in these patients was 30 months (maximum 85 months). The marginal radiation doses were 11 to 18 Gy (median 13 Gy), the maximum doses were 22 to 36 Gy (median 26 Gy), and the treatment volumes were 0.1 to 33 cm3 (median 2.7 cm3). The actuarial 5-year clinical tumor-control rate (no requirement for surgical intervention) for the entire series was 97.1+/-1.9%. Five-year actuarial rates for any new facial weakness, facial numbness, hearing-level preservation, and preservation of testable speech discrimination were 1.1+/-0.8%, 2.6+/-1.2%, 71+/-4.7%, and 91+/-2.6%, respectively. Facial weakness did not develop in any patient who received a marginal dose of less than 15 Gy (163 patients). Hearing levels improved in 10 (7%) of 141 patients who exhibited decreased hearing (Gardner-Robertson Classes II-V) before undergoing radiosurgery. According to multivariate analysis, increasing marginal dose correlated with increased development of facial weakness (p = 0.0342) and decreased preservation of testable speech discrimination (p = 0.0122).

CONCLUSIONS

Radiosurgery for acoustic neuroma performed using current procedures is associated with a continued high rate of tumor control and lower rates of posttreatment morbidity than those published in earlier reports.

Stereotactic radiosurgery versus stereotactic radiotherapy for patients with vestibular schwannoma: a Leksell Gamma Knife Society 2000 debate

✓ By definition, the term “radiosurgery” refers to the delivery of a therapeutic radiation dose in a single fraction, not simply the use of stereotaxy. Multiple-fraction delivery is better termed “stereotactic radiotherapy.” There are compelling radiobiological principles supporting the biological superiority of single-fraction radiation for achieving an optimal therapeutic response for the slowly proliferating, late-responding, tissue of a schwannoma. It is axiomatic that complication avoidance requires precise three-dimensional conformality between treatment and tumor volumes. This degree of conformality can only be achieved through complex multiisocenter planning. Alternative radiosurgery devices are generally limited to delivering one to four isocenters in a single treatment session. Although they can reproduce dose plans similar in conformality to early gamma knife dose plans by using a similar number of isocenters, they cannot reproduce the conformality of modern gamma knife plans based on magnetic resonance image—targeted localization and five to 30 isocenters.

A disturbing trend is developing in which institutions without nongamma knife radiosurgery (GKS) centers are championing and/or shifting to hypofractionated stereotactic radiotherapy for vestibular schwannomas. This trend appears to be driven by a desire to reduce complication rates to compete with modern GKS results by using complex multiisocenter planning. Aggressive advertising and marketing from some of these centers even paradoxically suggests biological superiority of hypofractionation approaches over single-dose radiosurgery for vestibular schwannomas. At the same time these centers continue to use the term radiosurgery to describe their hypofractionated radiotherapy approach in an apparent effort to benefit from a GKS “halo effect.” It must be reemphasized that as neurosurgeons our primary duty is to achieve permanent tumor control for our patients and not to eliminate complications at the expense of potential late recurrence. The answer to minimizing complications while maintaining maximum tumor control is improved conformality of radiosurgery dose planning and not resorting to homeopathic radiosurgery doses or hypofractionation radiotherapy schemes.

Brain metastasis from differentiated thyroid cancer in patients treated with radioiodine for bone and lung lesions

Brain metastasis of differentiated thyroid cancer (DTC) often is detected during treatment of other remote lesions. We examined the prevalence, risk factors and treatment outcome of this disease encountered during nuclear medicine practice. Of the 167 patients with metastasis to lung or bone treated 1-14 times with radioactive iodine (RAI), 9 (5.4%) also had lesions in the brain. Five were males and 4 females, aged 49-84, out of the original population of 49 males and 118 females aged 10-84 (mean 54.7) years. Three of them underwent removal of their brain tumors, 5 received conventional external beam irradiation, and 2 had stereotactic radiosurgery with supervoltage X-ray. None of the brain lesions showed significant uptake of RAI despite demonstrable accumulation in most extracerebral lesions. Seven patients died 4-23 (mean 9.4) months after the discovery of cerebral metastasis, brain damage being the primary or at least a contributing cause. The 8th and 9th patients remained relatively well for more than 42 and 3 months, respectively, without any evidence of intracranial recurrence. Our results confirmed that the brain is a major site of secondary metastasis from DTC. No statistically significant demographic risk factor was detected. Any suspicious neurological symptoms in the course of RAI treatment warrant cerebral computed tomography. As for therapy, from our initial experience, radiosurgery seemed promising as an effective and less invasive alternative to surgical removal.

Fractionated stereotactic radiosurgery and preservation of hearing in patients with vestibular schwannoma: a preliminary report

OBJECTIVE

Microsurgery and stereotactic radiosurgery (SRS) for vestibular schwannomas are associated with a relatively high incidence of sensorineural hearing loss. A prospective trial of fractionated SRS was undertaken in an attempt to preserve hearing and minimize incidental cranial nerve injury.

METHODS

Thirty-three patients with vestibular schwannomas were treated with 2100 cGy in three fractions during a 24-hour period using conventional frame-based linear accelerator radiosurgery. The median tumor diameter was 20 mm (range, 7-42 mm). Baseline and follow-up evaluations included audiometry and contrast-enhanced magnetic resonance imaging. End points were tumor progression, preservation of serviceable hearing, and treatment-related complications.

RESULTS

Thirty-one patients (32 tumors) were assessable for tumor progression and treatment-related complications and 21 patients for preservation of serviceable hearing, with a median follow-up interval of 2 years (range, 0.5-4.0 yr). Tumor regression or stabilization was documented in 30 patients (97%) and tumor progression in 1 (3%). The patient with tumor progression remains asymptomatic and has not required surgical intervention. Five patients (16%) developed trigeminal nerve injury at a median of 6 months (range, 4-12 mo) after SRS; two of these patients had preexisting trigeminal neuropathy. One patient (3%) developed facial nerve injury (House-Brackmann Class 3) 7 months after SRS. Preservation of useful hearing (Gardner-Robertson Class 1-2) was 77% at 2 years. All patients with pretreatment Gardner-Robertson Class 1 to 2 hearing maintained serviceable (Class 1-3) hearing as of their last follow-up examination.

CONCLUSION

Three-fraction SRS with a conventional stereotactic frame is feasible and well tolerated in the treatment of acoustic neuroma. This study demonstrates a high rate of hearing preservation and few treatment-related complications among a relatively high-risk patient cohort (tumors >15 mm or neurofibromatosis Type 2). Longer follow-up will be required to assess the durability of tumor control.

Improved trigeminal and facial nerve tolerance following fractionated stereotactic radiotherapy for large acoustic neuromas

The purpose of this study was to demonstrate improved cranial nerve tolerance following fractionated stereotactic radiotherapy for large acoustic neuromas, defined as tumours with pons-petrous distance (A) > 1 cm and midporous transverse diameter (A + Y) > 2 cm. Of 28 patients with acoustic neuromas treated with fractionated stereotactic radiotherapy, 19 had large tumours at high risk for radiosurgery-induced cranial neuropathy. Six patients received 36 Gy in six, weekly, fractions and 13 patients received 30 Gy in six, weekly, fractions. 15 patients had evaluable trigeminal nerve function and 16 had evaluable facial nerve function. At a median follow-up of 4.5 years, tumour shrinkage was seen in 10 patients and tumour size was stable in nine. None of the patients developed any evidence of transient, or permanent, trigeminal or facial neuropathy at any time during their follow-up period. Fractionated stereotactic radiotherapy may offer a superior therapeutic ratio to single fraction stereotactic radiosurgery in the management of large acoustic neuromas, as evidenced by the absence of post-treatment trigeminal and facial neuropathy.

[Fractionated irradiation of cerebellopontine angle neurinoma: 12 years' experience of the Bordeaux University Hospital Center]

PURPOSE

To evaluate retrospectively the long-term results of fractionated radiation therapy (RT) in cerebello-pontine angle neurinomas (CPA).

METHODS AND MATERIAL

From January 1986 to October 1995, 29 patients with stage III and IV neurinomas were treated with external fractionated RT. One patient was irradiated on both sides and indications for RT were as follows: (1) general contraindications for surgery (16 patients); (2) hearing preservation in bilateral neurinomas after controlateral tumor exeresis (six patients); (3) partial tumor removal (five patients); and, (4) non-surgical recurrence (three patients). A three to four fields technique with coplanar static beams and conformal cerobend blocks was used; doses were calculated on a 95 to 98% isodoses and were given five days a week for a median total dose of 51 Gy (1.8 Gy/fraction). Most patients were irradiated with 6 to 10 MV photons).

RESULTS

Median follow-up was 66 months (seven to 120 months). Seven patients died, two with progressive disease, five from non-tumoral causes. Tumor shrinkage was observed in 13 patients (43.3%), stable disease in 14 (46.6%), and tumor progression in three. Two patients underwent total tumor removal after RT (one stable and one growing tumor). Hearing was preserved in four out of six patients. No patient experienced facial or trigeminal neuropathy.

CONCLUSION

Fractionated RT is a well tolerated and efficacious treatment of large non-surgical CPA neurinomas.

Stereotactic radiosurgery in the management of acoustic neuromas associated with neurofibromatosis Type 2

OBJECT

Stereotactically guided radiosurgery is one of the primary treatment modalities for patients with acoustic neuromas (vestibular schwannomas). The goal of radiosurgery is to arrest tumor growth while preserving neurological function. Patients with acoustic neuromas associated with neurofibromatosis Type 2 (NF2) represent a special challenge because of the risk of complete deafness. To define better the tumor control rate and long-term functional outcome, the authors reviewed their 10-year experience in treating these lesions.

METHODS

Forty patients underwent stereotactic radiosurgery at the University of Pittsburgh, 35 of them for solitary tumors. The other five underwent staged procedures for bilateral lesions (10 tumors, 45 total). Thirteen patients (with 29% of tumors) had undergone a median of two prior resections. The mean tumor volume at radiosurgery was 4.8 ml, and the mean tumor margin dose was 15 Gy (range 12-20 Gy). The overall tumor control rate was 98%. During the median follow-up period of 36 months, 16 tumors (36%) regressed, 28 (62%) remained unchanged, and one (2%) grew. In the 10 patients for whom more than 5 years of clinical and neuroimaging follow-up results were available (median 92 months), five tumors were smaller and five remained unchanged. Surgical resection was performed in three patients (7%) after radiosurgery; only one showed radiographic evidence of progression. Useful hearing (Gardner-Robertson Class I or II) was preserved in six (43%) of 14 patients, and this rate improved to 67% after modifications made in 1992. Normal facial nerve function (House-Brackmann Grade 1) was preserved in 25 (81%) of 31 patients. Normal trigeminal nerve function was preserved in 34 (94%) of 36 patients.

CONCLUSIONS

Stereotactically guided radiosurgery is a safe and effective treatment for patients with acoustic tumors in the setting of NF2. The rate of hearing preservation may be better with radiosurgery than with other available techniques.

Radiation therapy for benign central nervous system disease

The most common indication for the use of radiation therapy in the treatment of benign central nervous system disease is for the treatment of benign brain tumors, such as meningioma, pituitary adenoma, acoustic neuroma, arteriovenous malformation, and craniopharyngioma. Other less common benign intracranial tumors treated with radiation include chordoma, pilocytic astrocytoma, pineocytoma, choroid-plexus papilloma, hemangioblastoma, and temporal bone chemodectomas. Benign conditions, such as histiocytosis X, trigeminal neuralgia, and epilepsy, are also amenable to radiation treatment. There have also been reports of radiosurgery being used for the treatment of movement disorders and psychiatric disturbances, such as obsessive-compulsive and anxiety disorders. For benign brain tumors, radiation therapy as either primary or adjuvant therapy plays an integral role in improving local control. In the treatment of trigeminal neuralgia, epilepsy, tremor, and some psychiatric disturbances, radiosurgery may help ameliorate or eliminate some symptoms. Patients with benign central nervous system disease are expected to live a long time. As such, treatment should be highly conformal and based on three-dimensional planning using magnetic resonance imaging, computed tomography, or both. It is critical that damage to normal brain be minimized.

Small-field fractionated radiotherapy with or without stereotactic boost for vestibular schwannoma

PURPOSE

To assess the efficacy and toxicity of small-field fractionated radiotherapy with or without stereotactic boost (SB) for vestibular schwannomas.

METHODS AND MATERIALS

Thirty-nine patients with vestibular schwannoma were treated with irradiation between March 1991 and February 1996. Extra-meatal tumor diameters were under 30 mm. Thirty-three patients received small-field fractionated radiotherapy followed by SB. Basic dose schedule was 44 Gy in 22 fractions over 5 1/2 weeks plus 4 Gy in one session. Six patients received small-field fractionated radiotherapy only (40-44 Gy in 20-22 fractions over 5-5 1/2 weeks or 36 Gy in 20 fractions over 5 weeks).dash;p >

RESULTS

Follow-up ranged from 6 to 69 months (median, 24 months). Tumors decreased in size in 13 cases (33%), were unchanged in 25 (64%), and increased in one (3%). The actuarial 2-year tumor control rate was 97%. Fifteen patients had useful hearing (Gardner-Robertson class 1-2) and 25 patients had testable hearing (class 1-4) before irradiation. The 2-year actuarial rates of useful hearing preservation (free of deterioration from class 1-2 to class 3-5) were 78%. The 2-year actuarial rates of any testable hearing preservation (free of deterioration from class 1-4 to class 5) were 96%. No permanent facial and trigeminal neuropathy developed after irradiation. The 2-year actuarial incidences of facial and trigeminal neuropathies were 8% and 16%, respectively.

CONCLUSIONS

Small-field fractionated radiotherapy with or without SB provides excellent short-term local control and a relatively low incidence of complications for vestibular schwannoma, although further follow-up is necessary to evaluate the long-term results.

[Stereotactic one-time irradiation (radiosurgery). The methods, indications and results]

BACKGROUND

Stereotaxy is a method to determine a point in the patient's body by an external coordinate system which is attached to the patient. Radiosurgery uses this method for precise delivery of a high single radiation dose to the patient. The aim is to destroy the tissue in the target and to spare surrounding unaffected normal tissue by a steep dose gradient.

METHODS

Three techniques of percutaneous radiosurgery are available: radiosurgery with ion beams with a cyclotron, spherical arrangement of cobalt-60 sources, the so-called gamma knife, and an adapted linear accelerator. The availability and the good clinical experience lead to a wide spread use of linear accelerator for radiosurgery in recent years. A subsequent development is fractionated stereotactic radiotherapy which combines the precision of radiosurgery with the radiobiological advantage of fractionation.

RESULTS

Only a few indications for radiosurgery are proven by statistically valid studies. One of these is the treatment of small arteriovenous malformation, where obliteration rates of 80% to 100% are reported with only minor toxicity. However, the obliteration rate is reduced significantly in large arteriovenous malformations. A local control rate of 90% is obtained after radiosurgery of brain metastases which is comparable to the results of microsurgical resection followed by adjuvant whole brain radiotherapy. An ongoing EORTC study evaluates the role of adjuvant whole brain radiotherapy after radiosurgery. The survival of the patients with brain metastases is limited by the existence of progressive extracerebral disease. The role of radiosurgery in the treatment of benign tumors is currently evaluated in clinical studies which include: vestibular schwannomas, meningiomas, chordomas and chondrosarcomas and pituitary adenomas. Most of the published studies include only small tumors because radiosurgery is limited by the risk of radionecrosis of adjacent normal tissue, which shows a steep dose volume response relationship. Recent developments of stereotactic radiotherapy include the use of mini-multileaf-collimators and clinical studies on stereotactic radiotherapy of extracranial targets.

CONCLUSIONS

Stereotactic irradiation is a well established treatment technique for intracranial tumors and arteriovenous malformations. Methods are available that allow optimization of dose distributions to irregularly shaped tumors for single dose as well as fractionated stereotactic irradiations by linear accelerator. Therefore the therapeutic potential of this technique has increased and enables also the extracerebral application in controlled clinical studies.

Update on vertigo management

Over the past decade, the treatment of vertigo has shifted from medical and surgical modalities in favor of physical therapy. When more aggressive treatment is necessary, patients may be treated with less invasive surgical modalities. This article provides an overview of recent advances.

Stereotactic radiosurgery for acoustic neuroma: a Canadian perspective

Stereotactically delivered radiation is now an accepted treatment for patients with acoustic neuroma. In some cases, patient preference may be the reason for its selection, while in others neurosurgeons may select it for patients who are elderly or have significant risk factors for conventional surgery. The majority of patients with acoustic neuroma treatment with stereotactic radiosurgery have been treated with the Gamma Knife, with follow ups of over 25 years in some instances. Other radiosurgery modalities utilizing the linear accelerator have been developed and appear promising, but there is no long-term follow up. Canada does not possess a Gamma Knife facility, and its government-funded hospital and medical insurance agencies have made it difficult for patients to obtain reimbursement for Gamma Knife treatments in other countries. We review the literature to date on the various forms of radiation treatment for acoustic neuroma and discuss the current issues facing physicians and patients in Canada who wish to obtain their treatment of choice.

Treatment planning optimization for linear accelerator radiosurgery

PURPOSE

Linear accelerator radiosurgery uses multiple arcs delivered through circular collimators to produce a nominally spherical dose distribution. Production of dose distributions that conform to irregular lesions or conformally avoid critical neural structures requires a detailed understanding of the available treatment planning parameters.

METHODS AND MATERIALS

Treatment planning parameters that may be manipulated within a single isocenter to provide conformal avoidance and dose conformation to ellipsoidal lesions include differential arc weighting and gantry start/stop angles. More irregular lesions require the use of multiple isocenters. Iterative manipulation of treatment planning variables can be difficult and computationally expensive, especially if the effects of these manipulations are not well defined. Effects of treatment parameter manipulation are explained and illustrated. This is followed by description of the University of Florida Stereotactic Radiosurgery Treatment Planning Algorithm. This algorithm organizes the manipulations into a practical approach for radiosurgery treatment planning.

RESULTS

Iterative treatment planning parameters may be efficiently manipulated to achieve optimal treatment plans by following the University of Florida Treatment Planning Algorithm. The ability to produce conformal stereotactic treatment plans using the algorithm is demonstrated for a variety of clinical presentations.

CONCLUSION

The standard dose distribution produced in linear accelerator radiosurgery is spherical, but manipulation of available treatment planning parameters may result in optimal dose conformation. The University of Florida Treatment Planning Algorithm organizes available treatment parameters to efficiently produce conformal radiosurgery treatment plans.

Analyses of neuro-otological complications after radiosurgery for acoustic neurinomas

PURPOSE

To find out the optimum treatment parameters and the proper indications for treatment of acoustic neurinomas, univariate and multivariate actuarial analyses of neuro-otological complications after stereotactic radiosurgery for acoustic neurinomas were performed.

METHODS AND MATERIALS

The subjects were 46 patients with acoustic neurinomas who underwent unilateral radiosurgery between June 1990 and June 1994 and were followed up at the University of Tokyo. Age ranged from 13 to 77 years (median, 54 years). Tumor diameter ranged from 0 to 25 mm (mean, 12 mm) at the cerebellopontine angle and from 2 to 15 mm (mean, 8.3 mm) in the internal auditory meatus. Maximum tumor doses ranged from 20 to 40 Gy (mean, 31.4 Gy), and peripheral doses from 12 to 25 Gy (mean, 16.8 Gy). One to eight isocenters were used (mean, 3.2). Median follow-up was 39 months. Eight events concerning neuro-otological complications were chosen, and the potential risk factors for them were analyzed by the actuarial analyses (univariate and multivariate). The events examined include hearing loss, vestibular function loss, facial palsy, and trigeminal nerve dysfunction. In order to point out potential risk factors for neuro-otological complications, univariate analyses were performed using both the Wilcoxon test and the log rank test, and multivariate analyses were performed with the Cox proportional hazards model. Variables nominated as potential risk factors were 1) demographic variables such as patient age and sex, 2) tumor dimensions, 3) treatment variables such as tumor doses and number of isocenters, and 4) pretreatment hearing levels. A variable with significant p-values (p < 0.05) in two or more of the three actuarial analyses (two univariate and one multivariate) was considered a possible risk factor.

RESULTS

The possible variables that increase the risk for each event analyzed were: neurofibromatosis type II (NF2) and the number of isocenters for total hearing loss; experience of prior operation, the tumor diameter in the internal auditory meatus, and NF2 for hearing threshold elevation; peripheral tumor dose for vestibular function loss; patient age or midporus transverse tumor diameter (the two variables were correlated), and the number of isocenters for facial palsy; and the number of isocenters for trigeminal neuropathy.

CONCLUSION

NF2 and the tumor diameter were the common risk factors for hearing loss in previous studies and ours. For the 5th/7th nerve dysfunction, the tumor diameter was the common risk factor. The risk of using more isocenters remains controversial. The difference in risk factors for hearing impairment and vestibular function loss suggests different mechanisms for the two. Further studies with larger populations and longer follow-up periods are required in order to draw conclusions on the risk factors in radiosurgery.

Dosimetric analysis and clinical implementation of 6 MV X-ray radiosurgery beam

The dosimetric data on tissue maximum ratios (TMR), output factors, off axis ratios and beam profiles are presented for small circular fields of diameters ranging from 12.5 to 40 mm for 6 MV radiosurgery beam. It is noticed that dmax increases as the collimator field size increases. Comparison of our data with the published TMR and output factors of similar small circular fields shows that our values are higher than those data. Similarities in trend are noticed with the published isodose volumes for 1-5 and 10 arcs. Not much variation is seen beyond two arcs for 80% isodose volumes for all the field sizes. The variation is small in 20% isodose volumes beyond three arcs. Variations are noticed in 5% isodose volumes for 12.5 mm diameter collimated beam. Our experience has been exclusively with malignant neoplasms. An ideal target volume is covered by 80% isodose volume with 3-4 arcs and a single isocenter. Sixteen patients have been treated to date at our institution, including one patient with brain metastases, two patients with meningiomas, one patient with lymphoma and 12 patients with astrocytomas. The majority of tumors have been treated with single isocenter but some as large as 7 cm have been treated safely with two isocenters.

Acoustic neuromas: results of current surgical management

OBJECTIVE

In this article, we review the surgical outcomes of 179 patients with acoustic neuromas.

METHODS

Most of the tumors (84%) were operated on using a retrosigmoid, transmeatal approach. A transpetrosal, retrosigmoid approach was used in 10% of the patients, most of whom had large tumors. The translabyrinthine (4%) and transmastoid, transpetrosal, partial labyrinthectomy approaches (2%) were used selectively. The operative approaches are discussed. Tumors were categorized according to their cerebellopontine angle dimensions as small (< 2 cm), medium (2.0-3.9 cm), and large (> or = 4 cm).

RESULTS

House-Brackmann evaluation of postoperative facial nerve function revealed excellent results (Grade I or II) in 96% of small tumors, 74% of medium tumors, and 38% of large tumors. A fair postoperative function (Grade III or IV) was achieved in 4% of small tumors, 26% of medium tumors, and 58% of large tumors. Functional hearing preservation, defined as Gardner-Robertson Class I or II, was achieved in 48% of small tumors and 25% of medium tumors. Hearing was not preserved in any of the three patients with large tumors in whom hearing preservation was attempted. Treatment complications consisted mainly of cerebrospinal fluid leakage (15% of the patients). The majority of the patients who experienced cerebrospinal fluid leakage were treated successfully with lumbar spinal drainage; only four patients (2% of the total group) required subsequent surgery for correction of cerebrospinal fluid leakage. There were two deaths (1%) in this series. One death occurred as the result of myocardial infarction and the other as the result of severe obstructive lung disease. One patient sustained disability because of cerebellar and brain stem injury. Complete tumor resection was accomplished in 99% of the patients, and there was no evidence of recurrence in this group. Only 1 of the 179 patients underwent incomplete tumor resection; he required subsequent surgery for symptomatic tumor regrowth. Our patient follow-up had a mean duration of 70 months and a median of 65 months (range, 3-171 mo).

CONCLUSION

Our results are similar to those of other large microsurgical series of acoustic neuromas. Unless a patient has major medical problems, microsurgery by an experienced team of surgeons is preferred over radiosurgery.

Management of 1000 vestibular schwannomas (acoustic neuromas): the facial nerve--preservation and restitution of function

OBJECTIVE

Although the rate of reported facial nerve preservation after surgery for vestibular schwannomas continuously increases, facial nerve paresis or paralysis is a frequent postsurgical sequelae of major concern. The major goal of this study was to define criteria for the right indication, timing, and type of therapy for patients with palsies despite anatomic nerve continuity and those with loss of anatomic continuity.

METHODS

One thousand vestibular schwannomas were surgically treated at the Department of Neurosurgery at Nordstadt Hospital from 1978 to 1993. Of 979 cases of complete removal and 21 cases of deliberately partial removal, the facial nerve was anatomically preserved in 929 cases (93%). The rate of preservation is increasing, as is evidenced in the most recent cases, and preservation is supported by special electrophysiological monitoring. The facial nerve was anatomically severed in 60 cases (6%). It was anatomically lost in previous operations that were performed elsewhere in 11 cases (1%). In case of nerve discontinuity (42 cases), immediate nerve reconstruction by one of three available intracranial procedures (within the cerebellopontine angle, intracranial-intratemporal, intracranial-extracranial) was performed in the same surgical setting. In case of loss of the proximal facial nerve stump at the brain stem, early reanimation by combination with the hypoglossal nerve was achieved in most patients within weeks after tumor surgery. In a few patients with anatomic nerve continuity but absence of reinnervation for 10 to 12 months, a hypoglossal-facial combination was applied. All the patients with partial or with complete palsies were treated in a special follow-up program of regular controls and of modulation of physiotherapeutic treatment every 3 to 6 months.

RESULTS

In intracranial nerve reconstruction at the cerebellopontine angle, 61 to 70% of patients regained complete eye closure and an overall result equivalent to House-Brackmann Grade 3. Hypoglossal-facial reanimation led to Grade 3 in 79%. The duration between the onset of paralysis and the reconstructive procedure is decisive for the quality of the outcome. These data are discussed in view of other treatment options and certain parameters influencing outcome.

CONCLUSIONS

This management contains three major principles as follows: 1) preservation of facial nerve continuity in function by the aid of intraoperative monitoring, 2) early nerve reconstruction in case of lost continuity, and 3) scheduled follow-up program for all patients with incomplete or complete palsies.

Risk analysis of linear accelerator radiosurgery

PURPOSE

To evaluate the toxicity of stereotactic single-dose irradiation and to compare the own results with already existing risk prediction models.

METHODS AND MATERIALS

Computed tomography (CT) or magnetic-resonance (MR) images, and clinical data of 133 consecutive patients treated with linear accelerator radiosurgery were analyzed retrospectively. Using the Cox proportional hazards model the relevance of treatment parameters and dose-volume relationships on the occurrence of radiation-induced tissue changes (edema, localized blood-brain barrier breakdown) were assessed.

RESULTS

Sixty-two intraparenchymal lesions (arteriovenous malformation (AVM): 56 patients, meningioma: 6 patients) and 73 skull base tumors were selected for analysis. The median follow-up was 28.1 months (range: 9.0-58.9 months). Radiation-induced tissue changes (32 out of 135, 23.7%) were documented on CT or MR images 3.6-58.7 months after radiosurgery (median time: 17.8 months). The actuarial risk at 2 years for the development of neuroradiological changes was 25.8% for all evaluated patients, 38.4% for intraparenchymal lesions, and 14.6% for skull base tumors. The coefficient: total volume recieving a minimum dose of 10 Gy (VTREAT10) reached statistical significance in a Cox proportional hazards model calculated for all patients, intraparenchymal lesions, and AVMs. In skull base tumors, the volume of normal brain tissue covered by the 10 Gy isodose line (VBRAIN10) was the only significant variable.

CONCLUSIONS

These results demonstrate the particular vulnerability of normal brain tissue to single dose irradiation. Optimal conformation of the therapeutic isodose line to the 3D configuration of the target volume may help to reduce side effects.

Preliminary results of linear accelerator radiosurgery for acoustic schwannomas

In this paper the authors evaluate the results of linear accelerator (LINAC)-based stereotactic radiosurgery for acoustic schwannomas. Fifty-six patients underwent LINAC-based stereotactic radiosurgery for acoustic schwannomas at the University of Florida between July 1988 and November 1994. Each patient was followed for a minimum of 1 year or until death; no patient was lost to follow up. One or more follow-up magnetic resonance images or computerized tomography scans were obtained in 52 of the 56 patients. Doses ranged between 10 and 22.5 Gy with 69.6% of patients receiving 12.5 to 15 Gy. Thirty-eight patients (68%) were treated with one isocenter and the dose was specified to the 80% isodose line in 71% of patients. Fifty-five patients (98%) achieved local control after treatment. The 5-year actuarial local control rate was 95%. At the time of analysis, 48 patients were alive and free of disease, seven had died of intercurrent disease, and one was alive with disease. Complications developed in 13 patients (23%). The likelihood of complications was related to the dose and treatment volume: 10 to 12.5 Gy to all volumes, three (13%) of 23 patients; 15 to 17.5 Gy to 5.5 cm3 or less, two (9%) of 23 patients; 15 to 17.5 Gy to more than 5.5 cm3, five (71%) of seven patients; and 20 to 22.5 Gy to all volumes, three (100%) of three patients. Linear accelerator-based stereotactic radiosurgery results in a high rate of local control at 5 years. The risk of complications is related to the dose and treatment volume.

Dose and diameter relationships for facial, trigeminal, and acoustic neuropathies following acoustic neuroma radiosurgery

PURPOSE AND OBJECTIVE

To define the relationships between dose and tumor diameter for the risks of developing trigeminal, facial, and acoustic neuropathies after acoustic neuroma radiosurgery, a large single-institution experience was analyzed.

MATERIALS AND METHODS

Two hundred and thirty-eight patients with unilateral acoustic neuromas who underwent Gamma knife radiosurgery between 1987-1994 with 6-91 months of follow-up (median 30 months) were studied. Minimum tumor doses were 12-20 Gy (median 15 Gy). Transverse tumor diameter varied from 0.3-5.5 cm (median 2.1 cm). The relationships of dose and diameter to the development of cranial neuropathies were delineated by multivariate logistic regression.

RESULTS

The development of post-radiosurgery neuropathies affecting cranial nerves V, VII, and VIII were correlated with minimum tumor dose and transverse tumor diameter (P < 0.01 for all except Dmin for VIII where P = 0.10). A comparison of the dose-diameter response curves showed the acoustic nerve to be the most sensitive to doses of 12-16 Gy and the facial nerve to be the least sensitive.

CONCLUSION

The risks of developing trigeminal, facial, and acoustic neuropathies following acoustic neuroma radiosurgery can be predicted from the transverse tumor diameter and the minimum tumor dose using models constructed from data presently available.

Evolution in technique for vestibular schwannoma radiosurgery and effect on outcome

PURPOSE

To define changes in treatment technique for vestibular schwannoma radiosurgery and to relate them to changes in outcome, a large single institution experience was reviewed.

METHODS AND MATERIALS

Two hundred seventy-three patients with unilateral vestibular schwannomas underwent Gamma knife radiosurgery: 118 with computed tomography (CT) treatment planning during 1987-1991, and 155 with magnetic resonance imaging (MR) treatment planning in 1991-1994. Mean treatment parameters differed between the CT and MR groups: minimum tumor dose (D(min)) was 17 vs. 14 Gy, number of isocenters was 3.4 vs. 5.8, and volume was 3.5 vs 2.7 cc., respectively.

RESULTS

The actuarial 7-year clinical tumor control rate (no requirement for surgical intervention) for the entire series was 96.4 +/- 2.3%, with a radiographic tumor control rate of 91.0 +/- 3.4%; these rates were similar for the CT and MR groups. Significantly lower rates of postradiosurgery facial, trigeminal, and auditory neuropathy were observed in the MR group compared to the CT group. Multivariate analyses found significant independent correlations of increasing rates of facial and trigeminal neuropathy with increasing transverse tumor diameter and D(min), as well as with CT treatment planning (compared to MR). Decreased hearing was similarly correlated with diameter and CT planning but not with D(min).

CONCLUSIONS

Changes in radiosurgery technique and the use of lower doses improved the outcome after vestibular schwannoma radiosurgery by decreasing cranial neuropathy rates. MR-based treatment planning appears to have significantly contributed to this improvement. Despite decreases in radiation dose, no change in the high rate of tumor control has yet been observed.

Fractionated stereotactic radiotherapy for the treatment of acoustic neuromas: preliminary results

PURPOSE

To evaluate the efficacy and toxicity of fractionated, stereotactic radiotherapy (SRT) for acoustic neuromas.

METHODS AND MATERIALS

Twelve patients with acoustic neuroma were treated with SRT between June 1992 and October 1994. Follow-up ranged from 16-44 months. Patient age ranged from 27-70 (median: 45). Eight patients were treated with primary SRT and four patients were treated after primary surgical intervention for recurrent [3] or persistent [1] disease. Tumor volumes were 1.2-18.4 cm3 (median: 10.1 cm3). Collimator sizes ranged from 30-50 mm (median: 37.5). Tumors received 1.8 Gy/day normalized to the 95% isodose line. Patients received a minimum prescribed dose of 54 Gy in 27-30 fractions over a 6-week period.

RESULTS

After a median follow-up of 26.5 months, local control was obtained in 12 out of 12 lesions. Tumor regression was noted in three patients, and tumor stabilization was found in the remaining nine patients. No patient developed a new cranial nerve deficit. One patients developed worsening of preexisting Vth cranial neuropathy and another experienced a decrease in hearing. However, all nine patients with useful hearing prior to SRT maintained useful hearing at last follow-up.

CONCLUSIONS

Stereotactic radiotherapy provided excellent local control without new cranial nerve deficits. These results must be viewed as tentative in nature because of the small number of patients and the short median follow-up period.