A Protective Cap: Fundal Fluid Cap Facilitates a Reduction in Inner Ear Radiation Dose in the Radiosurgical Treatment of Vestibular Schwannoma. Issue 2 (February 2021)

• Record Type: Journal Article
• Authors: Bojrab, Dennis I.; Fritz, Christian G.; Lin, Kenny F.; Schutt, Christopher A.; Hong, Robert S.; Babu, Seilesh C.; Chen, Peter Y.; Maitz, Ann; Bojrab, Dennis I.
• Is Part Of: Otology & neurotology. Volume 42:Issue 2(2021)
• Publication Date: 2021-02
• Subjects: Cochlear dose -- Fundal fluid -- Gamma Knife -- Hearing preservation -- Labyrinth dose -- Stereotactic radiosurgery -- Vestibular schwannoma; Otology -- Periodicals; Ear -- Diseases -- Periodicals; Skull base -- Surgery -- Periodicals; 617.8005
• DOI: 10.1097/MAO.0000000000002856
• Languages: English
• ISSNs: 1531-7129

Abstract

Abstract : Objective: Assess inner ear radiation dose magnitude as it relates to fundal cap length and hearing outcomes in the radiosurgical treatment of vestibular schwannoma. Study Design: Retrospective case series. Setting: Tertiary neurotology referral center. Patients: Patients treated with Gamma Knife radiosurgery for vestibular schwannoma between March 2007 and March 2017 were considered for this study. Exclusion criteria included pretreatment pure-tone average (PTA) >90 dB, neurofibromatosis type II, history of previous surgical resection, and follow-up less than 1 year. Main Outcome Measure: (s): Hearing function was assessed by maintenance of class A/B hearing level and maintenance of baseline hearing (⩽20 dB change in PTA following Gamma Knife radiosurgery). Results: Lower radiation doses delivered to the inner ear were associated with longer fundal cap lengths: mean cochlear dose (r = −0.130; p = 0.184), mean labyrinth dose (r = −0.406; p < 0.001), max cochlear dose (r = −0.326; p = 0.001), and max labyrinth dose (r = −0.360; p < 0.001). Kaplan–Meier analysis with log-rank testing revealed that patients with a mean labyrinth dose < 3 Gy achieved higher rates of preserving baseline hearing (⩽20 dB change in PTA) following radiosurgery, compared to patients with a mean labyrinth dose ≥3 Gy ( p < 0.001). A fundal fluid cap length of 2.5 mm was associated with the 3 Gy mean labyrinth dose threshold. Conclusions: We report that fundal cap presence facilitated the creation of treatment plans with a lower dose delivered to the labyrinth. By affording this dose reduction, a fundal cap may be associated with a slight improvement in hearing outcomes. Abstract : Supplemental Digital Content is available in the text