This article investigates the role of radiosurgery and stereotactic radiotherapy in the management of vestibular schwannomas (VS), reviewing the authors’ own prospective cohort and the current literature. For patients with large Stage IV VS (according to the Koos classification), a combined approach with deliberate partial microsurgical removal followed by radiosurgery to the residual tumor is proposed. The authors’ cohort is unique with respect to the size of the population and the length of the follow-up, and demonstrates the efficacy and safety of VS radiosurgery, with particular regard to its high rate of hearing preservation.
Key points
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The superior safety of radiosurgery over microsurgery in small to middle-sized vestibular schwannomas (VS) has been demonstrated in 5 prospective comparative studies, all of which used Gamma Knife radiosurgery. Normal facial movement and functional hearing are more likely to be preserved with radiosurgery than with microsurgery.
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For large Koos Stage IV VS, a combined approached with a deliberate subtotal tumor removal and functional monitoring followed by radiosurgery of the remnant reduces the risk of facial nerve palsy in comparison with radical tumor removal.
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Multisession radiosurgery (stereotactic radiotherapy) has not yet been proved to have any advantages over single-session, high-precision radiosurgery.
Introduction
Within the last 3 last decades, microsurgery and stereotactic radiosurgery (SRS) have become well established management options for vestibular schwannomas (VS). Advancement in the management of VS can be separated into 3 periods: the microsurgical pioneer period; the demonstration of SRS as a first-line therapy for small to medium-sized VS; and, at present, a period of SRS maturity based on a large worldwide patient accrual.
Owing to the young age and the benign nature of the lesion, long life expectancy, and the potential severity of functional risks, in the modern era VS should be managed by experienced multidisciplinary teams who are able to integrate all microsurgical and radiosurgical approaches to provide the highest level of care, the highest probability of functional preservation, and a good quality of life. Modern literature provides us with sufficient evidence that the series must include high patient volumes with sufficiently long-term follow-up. This research has enabled us to identify the potential roles and limitations of each technique.
Introduction
Within the last 3 last decades, microsurgery and stereotactic radiosurgery (SRS) have become well established management options for vestibular schwannomas (VS). Advancement in the management of VS can be separated into 3 periods: the microsurgical pioneer period; the demonstration of SRS as a first-line therapy for small to medium-sized VS; and, at present, a period of SRS maturity based on a large worldwide patient accrual.
Owing to the young age and the benign nature of the lesion, long life expectancy, and the potential severity of functional risks, in the modern era VS should be managed by experienced multidisciplinary teams who are able to integrate all microsurgical and radiosurgical approaches to provide the highest level of care, the highest probability of functional preservation, and a good quality of life. Modern literature provides us with sufficient evidence that the series must include high patient volumes with sufficiently long-term follow-up. This research has enabled us to identify the potential roles and limitations of each technique.
Vestibular schwannoma radiosurgery
Between July 1992 and June 2011, 3050 VS were operated on in the Department of Functional Neurosurgery of Timone University Hospital in Marseille, France. All 3050 of these patients have been included in the series reported here. Patients were preoperatively evaluated and prospectively followed up with a clinical evaluation including Pure Tone Audiometry (PTA), Speech Discrimination Score (SDS), vestibulometry, Schirmer test, and serial magnetic resonance imaging scans (recommended at 6 months, then at 1, 2, 3, 5, 7, 10, and 15 years). One hundred forty-eight patients had neurofibromatosis type II (NF II). Follow-up of 3 years or more was available for 2336 patients (patients with NF II excluded). The mean age was 66.3 years. Tumor classification according to Koos stage was I (17.6%), II (51.8%), III (27%), and IV (3.6%). Initial symptoms were hypoacusia in 49.5% of patients, tinnitus in 19.4%, and vertigo in 13.2%, while 5.1% experienced instability. A history of sudden hearing loss was reported in 21.5%. Of note, microsurgical resection of the VS had been performed before SRS in 7% of patients. The day before intervention, hypoacusia was reported in 87% of patients, tinnitus in 65%, imbalance in 52%, vertigo in 31%, facial palsy in 8.2%, hemifacial spasm in 7.5%, trigeminal neuralgia in 5.3%, and facial hypoesthesia in 4.8%. The methodology has been previously described.
Defining the limits of the tumor is first done on the stereotactic 3-dimensional T1-weighted gadolinium-enhanced MR sequence. The absence of distortion between the MR and stereotactic computed tomography (CT) scan is systematically checked, and a shift in the dose plan is performed consequently if and when necessary. The limits of the internal auditory canal, vestibule, semicircular canals, and cochlea are defined on CT. Dosimetry corresponding to the cisternal portion of the tumor, and adjacent cochlear and facial nerve, respectively, are corrected according to high-resolution T2-weighted imaging (CISS; Siemens) with and without contrast. The dose to the margin is 12 Gy for patients with poor hearing (Gardner-Robertson ≥3) and 11 Gy if hearing is still serviceable. The dose-selection policy has not changed since 1992 for VS, which confers a very good homogeneity to this series. Patients were treated using a Gamma Knife (GK), models B, 4, 4C, and Perfexion, over this time interval.
Clinical outcomes
The prospective cohort of Timone Hospital demonstrates, in the last of neuroimaging (MR) follow-ups, tumor control in 97.5% of the patients. In the patients with continuous growth of the VS at the 3-year mark (2.5%), the authors have consequently been led to propose repeat SRS (20 patients) or a resection (39 patients). MRI follow-up during the first year revealed an average 20% increase in tumor volume, followed thereafter by stabilization at 3 years after radiosurgery. After the third year a decrease in tumor volume was typically observed ( Fig. 1 ). At 7 years the volume corresponds to 60% of the volume at time of SRS (40% decrease). The rate of transient facial palsy was less than 0.5%. This rate was 3% during the first period, corresponding to the learning curve (with the first 100 patients). The rate was subsequently reduced to 1.4% during the period preceding the introduction of the workstations (involving 212 patients), and dropped further to 0.5% after the introduction of the dose-planning workstations, and their integration in anatomic imaging (360 patients). Since the introduction of robotization (2319 patients), this rate of transient facial palsy has virtually disappeared in unilateral VS.
In addition, between 2005 and 2010 an extensive search and cross-referencing exercise was conducted on PubMed, which uncovered 213 articles. Of these, 55 reported on a series of more than 30 patients, providing the authors with safety efficacy data. A second filtering enabled the ruling out of any duplicated series and general review articles (15 articles). The majority are retrospective studies. However, 3 studies were prospective, reporting on 69, 78, and 111 patients, respectively. The main series reported and their results are summarized in Table 1 . These series are very heterogeneous in terms of radiation-delivery techniques, size of tumors, doses used, inclusion or exclusion of NF II patients, the number of patients who had been operated on previously, methods of measurement, definition of tumor control, and overall duration of follow-up time, from when the patient is released postsurgery to the final outpatient visit.
| Authors, Ref. Year | Population/Previous Surgery | Volume (cm 3 ) | Marginal Dose (Gy) | Follow-Up (mo) Lost to Follow-Up | Tumor Control (%) | V (%) | VII (%) | VIII (%) |
|---|---|---|---|---|---|---|---|---|
| Gamma Knife | ||||||||
| Chung et al, 2005 R | 195 39% | 4.1 (0.04–23.1) | 13 (11–18.2) | 31 (1–110) 2 lost | At 10 y: 96.8 | 1.1 | 1.5 | 60 |
| Lunsford et al, 2005 R | 829 20% | 2.5 | 13 (10–20) | NR >10 y 252 pts | At 10 y: 98 | 3.1 | <1 | 78.6 |
| Wowra et al, 2005 R | 111 33.3% | 1.6 (0.08–8.7) | 13 (10–16) | 7 y (5–9.6) | At 6 y: 95 | 2.7 | 2.7 | NR |
| Van Eck et al, 2005 P | 78 NR | 2.28 (0.1–11.7) | 13–20 | 22 | 97.4 | 3.8 | 1.2 | 69.2 |
| Hasegawa et al, 2005 R | 317 22.7% | 5.6 (0.2–36.7) GR 1–2: 30.6% | 13.2 (10–18) | 93 29 lost | 94.4 (10 y: 92) | 2 | 2 a | 67.5 |
| Hempel et al, 2006 R | 123 NR | 1.6 (0.1–9.9) | 13 (10–14.5) | 98 (63–129) | NR | 5.8 | 0 | NR |
| Liu et al, 2006 R | 74 25.6% | 10.8 (0.11–27.8) | 12.3 (12–14) | 68.3 (30–122) | 95.9 at 5 & 10 y | 7 | 5 | 72.3 |
| Hudgins et al, 2006 R | 159 NR | 3.3 | 14 (8–20) | 12 y | 96.4 | 0 | 0 | NR |
| Chopra et al, 2007 R | 216 0% | 1.3 (0.08–37.5) | 13 (12–13) | 68 (max: 143) | 98.3 at 10 y | 3.7 | 0 | 56.6 |
| Niranjan et al, 2008 R | 96 NR | 0.112 mm 3 (0.1–0.5) Koos I | 13 (10–18) | 28 (12–144) | 99 | 0 | 0 | 63.3 |
| Régis et al, 2008 P | 184 0% | NR GR 1 & 2 | 12 | 7 y (3–13) | NR | 0.6 | 0.7 | At 3 y: 60 |
| Timmer et al, 2009 P | 69 NR | 2.28 (0.02–10.2) | 11 (9.3–12.5) | 14 (3–56) 16 lost | NR | 9 | 7 | 75 |
| Kano et al, 2009 R | 77 0% | 0.75 (0.07–7.7) GR 1: 46/GR 2: 31 | 12.5 (12–13) | 20 mo (6–40) | 97.4 | NR | 0 | At 1 y 89.3, at 2 y 66.8 |
| Tamura et al, 2009 P | 74 0% | 1.35 (0.06–4.6) GR 1 | 12 (9–13) | 55.6 (3–11 y) | 93 | NR | 0 | 78.4 at 3 y |
| Franzin et al, 2009 R | 50 0% | 0.73 (0.03–6.6) GR 1 or 2 | 13 (12–16) | 36 (6–96) | 96 | NR | 0 | 68 |
| Present series P | 2087 7% | 2.63 GR 1 & 2: 46% | 12.3 | Minimum 3 y | 97.5 | 0.5 | 0.5 | 63 |
| LINAC | ||||||||
| Friedman et al, 2006 R | 390 20% | NR | 12.5 (10–22.5) | 40 42 lost | At 5 y: 90 | 3.6 | 4.4 | NR |
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