Abstract
BackgroundStereotactic radiosurgery (SRS) is a common treatment option for vestibular schwannomas. Historically, a dose de-escalation of the marginal prescribed dose from 16 Gy to 12–13 Gy has been done to limit toxicity without reducing local control (LC). We aimed to retrospectively report outcomes of Linac-based SRS for vestibular schwannomas treated with different doses.MethodsIncluded in the study were 97 stage 1 (1%), 2 (56%), 3 (21.5%), and 4 (21.5%) vestibular schwannomas treated with Linac-based (Novalis®) SRS from 1995 to 2019. No margin was added to the GTV to create the PTV. The median marginal prescribed dose was 14 Gy (range: 12–16 Gy) before 2006 and then 11 Gy for all patients (61 pts). Mean tumor volume was 1.96 cm3, i.e., about 1.6 cm in diameter. Mean follow-up was 8.2 years.ResultsFollowing SRS, LC at 3, 5, and 10 years was 100%, 98.4%, and 95.6%, respectively [100% for those with ≤ 13 Gy as the marginal prescribed dose (NS)]. Toxicity to the trigeminal nerve was reported in 7.2% of cases (3.3% and 0% for transient and permanent toxicity for 11 Gy). The marginal prescribed dose was the only significant predictive factor in univariate and multivariate analysis (HR = 1.77, 95% CI = 1.07–3.10, p = 0.028). Toxicity to the facial nerve was reported in 6.2% of cases. The marginal prescribed dose was again the only significant predictive factor in univariate and multivariate analysis (HR = 1.31, 95% CI = 0.77–2.23, p = 0.049).ConclusionLinac-based SRS for stages 1–3 vestibular schwannomas provides excellent outcomes: a 10-year LC rate of over 95%, with a permanent facial or trigeminal toxicity rate of under 5%. A marginal prescribed dose of 11 Gy seems to decrease nerve toxicity and facial toxicity in particular, without reducing LC. Prospective studies with longer follow-up are needed.
Highlights
Vestibular schwannomas are the most frequent tumors of cranial nerves with an incidence rate of 1 to 2 per 100,000 people
The strength of our study lies in the length of patient followup: an average of 8.2 years, including 16 years for patients with marginal prescribed doses of over 11 Gy. 5-year local control (LC) was excellent, with an absence of local failure for patients treated with a marginal prescribed dose of 11 Gy and was not significantly different from LC for patients with marginal prescribed doses of over 11 Gy (100% vs. 98%, p = 0.3)
10 studies have been published about Linear Accelerator (Linac)-based Stereotactic Radiosurgery (SRS) for vestibular schwannomas [18, 21,22,23,24,25,26,27,28,29]
Summary
Vestibular schwannomas are the most frequent tumors of cranial nerves with an incidence rate of 1 to 2 per 100,000 people. They are often unilateral, slightly more common in women and occur in patients with a mean age of 55 years [1, 2]. The aim of treatment is local control (LC) while preserving the nerves of the pontocerebellar angle (especially the trigeminal and the facial nerves). For stage 1 (intra-canal) and 2 (extra-canal with invasion of the pontocerebellar angle without contact with the cerebellum or the brainstem) vestibular schwannomas which are progressive or symptomatic, either surgery or radiotherapy may be proposed without significant difference in terms of efficacy (LC ≈ 90%) [4]. We aimed to retrospectively report outcomes of Linac-based SRS for vestibular schwannomas treated with different doses
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