Abstract
Vestibular schwannomas (VSs) are benign, slow-growing tumors. Management options include observation, surgery, and radiation. In this retrospective trial, we aimed at evaluating whether biologically effective dose (BED) plays a role in tumor volume changes after single-fraction first intention stereotactic radiosurgery (SRS) for VS. We compiled a single-institution experience (n = 159, Lausanne University Hospital, Switzerland). The indication for SRS was decided after multidisciplinary discussion. Only cases with minimum 3 years follow-up were included. The Koos grading, a reliable method for tumor classification was used. Radiosurgery was performed using Gamma Knife (GK) and a uniform marginal prescription dose of 12 Gy. Mean BED was 66.3 Gy (standard deviation 3.8, range 54.1–73.9). The mean follow-up period was 5.1 years (standard deviation 1.7, range 3–9.2). The primary outcome was changes in 3D volumes after SRS as function of BED and of integral dose received by the VS. Random-effect linear regression model showed that tumor volume significantly and linearly decreased over time with higher BED (p < 0.0001). Changes in tumor volume were also significantly associated with age, sex, number of isocenters, gradient index, and Koos grade. However, the effect of BED on tumor volume change was moderated by time after SRS and Koos grade. Lower integral doses received by the VSs were inversely correlated with BED in relationship with tumor volume changes (p < 0.0001). Six (3.4%) patients needed further intervention. For patients having uniformly received the same marginal dose prescription, higher BED linearly and significantly correlated with tumor volume changes after SRS for VSs. BED could represent a potential new treatment paradigm for patients with benign tumors, such as VSs, for attaining a desired radiobiological effect. This could further increase the efficacy and decrease the toxicity of SRS not only in benign tumors but also in other SRS indications.
Highlights
Vestibular schwannomas (VSs) are rising from the Schwann cells, which usually wrap around motor and sensory nerves and, for this particular case, the V III−th cranial nerve [4]
We further suggested that biologically effective dose (BED) can be a better predictor as compared with the prescribed marginal dose for obliteration of arteriovenous malformations after single-fraction radiosurgery, using a uniform dose prescription [29]
The univariate analysis showed that increasing the BED by one unit was associated with tumor volume decrease of − 0.27 (95% confidence interval (CI) [− 0.31, − 0.24], p < 0.0001) in average (Fig. 2)
Summary
Vestibular schwannomas (VSs) are rising from the Schwann cells, which usually wrap around motor and sensory nerves and, for this particular case, the V III−th cranial nerve [4]. Patients may experience different specific symptoms, of whom most common is unilateral hearing loss, ringing in the ear (tinnitus), dizziness, facial numbness (if compression of the trigeminal nerve), and rarely facial weakness (if major compression of facial nerve). It has been classically considered that VSs are slowgrowing tumors, with an average rate of 1 mm/year [23]. Recent research suggests that the majority of VSs might experience volumetric growth, with about onethird growing at a rate of 100% per year [27]. There is currently no consensus with regard to patient’s selection for therapeutic intervention, recent studies suggested radiosurgery (in contrast to observation) for small VSs in patients not choosing surgical resection [15]. The outcome goals for both patients and medical staff are tumor control on longterm basis, while preserving cranial nerve function and high quality of life
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