Inherent Functional Dependence Among Cochlear Dose Surrogates for Stereotactic Radiosurgery of Vestibular Schwannomas

Publication date: Available online 20 August 2016
Source:Practical Radiation Oncology
Author(s): Lijun Ma, Steve E. Braunstein, Philip V. Theodosopoulos, Michael W. McDermott, Penny K. Sneed
PurposeVarious cochlear dose surrogates have been reported as associated with hearing outcome in studies of stereotactic radiosurgery (SRS) for vestibular schwannomas. In this study, we investigated whether an inherent functional relationship exits among these reported surrogates.Methods and MaterialsA cohort of 85 serial patient cases treated with single-fraction stereotactic radiosurgery from 1997–2013 at our institution was analyzed. For all the cases, the mean prescription dose was 12.5±0.3Gy (range, 12–13Gy) and mean target volume 1.32±1.51mL (range, 0.80–8.77mL). The mean cochlea volume was 0.078±0.016mL (range, 0.048–0.131mL; median, 0.076mL). Correlation analysis among mean cochlear dose, point maximum dose and modiolus dose was performed and also parameterized with new variables such as the Effective Dose Radius (EDR) as derived from a general dose fall-off model.ResultsWeak correlation via linear regression was found between the point maximum dose and the mean cochlear dose (R²=0.719) as well as the modiolus dose (R²=0.568). However, when parameterized with EDR, a near perfect correlation (p<0.0001) via linear regression was found between the EDR for the point maximum dose and the EDR for the mean cochlear dose (R²=0.996), and with the EDR for the modiolus dose (R²=0.993). Such a result led to a functional formula relating these dose surrogates, yielding dose equivalence results such as: 12Gy point maximum dose is equivalent to mean cochlear dose of 5.6±0.1Gy (95% CL), or modiolous dose of 6.0±0.2Gy (95% CL).ConclusionsAn inherent functional relationship was found among point maximum, modiolus, and mean cochlear doses for SRS of vestibular schwannomas. As such, clinical hearing outcome can be interchangeably analyzed or reported via any of these dose surrogates.



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