The Relevance of Biologically Effective Dose for Hearing Preservation After Stereotactic Radiosurgery for Vestibular Schwannomas: A Retrospective Longitudinal Study

Abstract

BACKGROUND:Stereotactic radiosurgery has become a common treatment approach for small-to-medium size vestibular schwannomas.OBJECTIVE:To evaluate relationship between time (beam-on and treatment) and risk of hearing decline after stereotactic radiosurgery for vestibular schwannomas in patients with Gardner–Robertson (GR) baseline classes I and II.METHODS:This retrospective longitudinal single-center study included 213 patients with GR I and II treated between June 2010 and December 2019. Risk of passing from GR classes I and II (coded 0) to other classes III, IV, and V (coded 1) and the increase in pure tone average (continuous outcome) were evaluated using a mixed-effect regression model. Biologically effective dose (BED) was further assessed for an alpha/beta ratio of 2.47 (Gy2.47).RESULTS:Binary outcome analysis revealed sex, dose rate, integral dose, time [beam-on time odds ratio 1.03, P = .03, 95% CI 1.00-1.06; treatment time (P = .02) and BED (P = .001) as relevant. Fitted multivariable model included the sex, dose rate, and BED. Pure tone average analysis revealed age, integral dose received by tumor, isocenter number, time (beam-on time odds ratio 0.20, P = .001, 95% CI 0.083-0.33) and BED (P = .005) as relevant.CONCLUSION:Our analysis showed that risk of hearing decline was associated with male sex, higher radiation dose rate (cutoff 2.5 Gy/minute), higher integral dose received by the tumor, higher beam-on time ≥20 minutes, and lower BED. A BED between 55 and 61 was considered as optimal for hearing preservation.

Impact of the Mean Cochlear Biologically Effective Dose on Hearing Preservation After Stereotactic Radiosurgery for Vestibular Schwannoma: A Retrospective Longitudinal Analysis

“…GK, Gamma Knife; GR, Gardner–Robertson; PTA, pure tone average.Adapted from the study by Tuleasca et al, 18 by permission from the Congress of Neurological Surgeons.…”

“…Adapted from the study by Tuleasca et al, 18 by permission from the Congress of Neurological Surgeons.…”

“…Earlier studies have shown that in vestibular schwannomas, BED received by the tumor correlates with hearing decline. 1a , 2a This study evaluates the relevance of BED to the cochlea in hearing preservation.…”

“…8,[10][11][12][13] Key factors for hearing preservation after SRS for VSs have been considered the mean dose received by the cochlea, [14][15][16] the maximal dose received by the ventral cochlear nucleus, 17 or, more recently, the biologically effective dose (BED) received by the tumor. 8,18 It is thus considered that cochlear dose might be one of the many variables associated with hearing preservation after SRS for VSs. 19 A key question is whether the BED received by the cochlea would be more relevant as compared with the physical dose, considering that BED incorporates not only the factor time but also the delivered dose.…”

“…8,10-13 Key factors for hearing preservation after SRS for VSs have been considered the mean dose received by the cochlea, 14-16 the maximal dose received by the ventral cochlear nucleus, 17 or, more recently, the biologically effective dose (BED) received by the tumor. 8,18…”