Clinical Evaluation of CyberKnife in the Treatment of Vestibular Schwannomas

Abstract

Objective. This study assessed the posttreatment tumor control and auditory function of vestibular schwannoma (VS) patients after CyberKnife (CK) and analyzed the possible prognostic factors of hearing loss. Methods. We retrospectively studied 117 VS patients, with Gardner-Robertson (GR) classification grades I to IV, who underwent CK between 2006 and 2012. Data including radiosurgery treatment parameters, pre- and postoperative tumor size, and auditory function were collected and examined. Results. With CK, 117 patients had excellent tumor control rates (99.1%), with a mean imaging followup of 61.1 months. Excluding 52 patients (GR III-IV pretreatment), 53 (81.5%) of the remaining 65 patients (initial GR I-II) maintained GR I or II hearing after CK, with a mean audiometric followup of 64.5 months. Twelve patients experienced hearing degradation (91.6% were GR II pretreatment); they appeared to have significantly larger tumor sizes, significantly smaller cochlear sizes, and higher prescribed cochlear doses, compared to the patients with preserved hearing. Conclusion. Our data showed that CK treatment provided an excellent tumor control rate and a comparable hearing preservation rate in VS patients. Patients with pretreatment GR II hearing levels, larger tumor volumes, smaller cochlear sizes, and higher prescribed cochlear doses may have poor hearing prognoses.

Long-term Treatment Response and Patient Outcomes for Vestibular Schwannoma Patients Treated with Hypofractionated Stereotactic Radiotherapy

“…Fractionated SRT provides the benefit of delivering a lower dose of radiation during each treatment visit to such critical structures, rather than the high-dose radiation delivered by SRS. Thus far, the majority of studies of hearing preservation after HSRT demonstrate that greater than half of patients have preserved serviceable hearing (42–81%; Table 6 ) ( 3 , 9 , 10 , 32 , 33 , 35 – 37 ), although gradient deterioration of pure tone averages has been observed even in those with hearing preservation ( 7 ). Hayden Gephart et al comment that a higher radiation dose and larger cochlear volume within the radiation field result in poorer hearing outcomes posttreatment ( 37 ).…”

Radiotherapy for vestibular schwannoma: Review of recent literature results

“…In this report, patients with larger tumour volumes, smaller cochlear sizes and higher prescribed cochlear doses had poor hearing prognosis. 21 In a recent retrospective analysis of 73 cases (63 primary and 10 postsurgical radiosurgery), Vivas et al described linear accelerator (LINAC) based FSRT for VS (18 Gy over 3 fractions at 80% isodose). 22 Analysis for tumour growth was positive for 17% using linear (maximum diameters) and 26% using volumetric measurements.…”

Vestibular Schwannomas: Surgical and Nonsurgical Management

“…There is also significant variability in how successful tumor control or hearing preservation is defined. For example, some studies define successful tumor control as no growth on follow-up imaging [35,47,50,51], while others report a lack of symptomatic growth or progression that required further treatment [31,42,49]. To illustrate, Vivas [31] reported tumor growth rates and percentage of patients that progressed to further intervention.…”

“…Despite limitations, STR is an effective means of tumor control with reported rates at 71-99 % [29,31,33,35,47,[50][51][52][53]. The variability in control rates reflects a lack of unified parameters whereby in general improved tumor control rates are defined as no growth on follow-up imaging [35].…”

“…7]. However, many studies reporting control rates fail to clarify whether the tumor demonstrated growth prior to STR [42,47,49,[51][52][53]. Therefore, in many studies, it is unclear if the lack of tumor growth is a result of STR or whether the tumor naturally was not growing.…”