Progression of hearing loss after LINAC-based stereotactic radiotherapy for vestibular schwannoma is associated with cochlear dose, not with pre-treatment hearing level

Abstract

BackgroundAlthough stereotactic radiotherapy (SRT) for vestibular schwannoma has demonstrated excellent local control rates, hearing deterioration is often reported after treatment. We therefore wished to assess the change in hearing loss after SRT and to determine which patient, tumor and treatment-related factors influence deterioration.MethodsWe retrospectively analyzed progression of hearing loss in patients with vestibular schwannoma who had received stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT) as a primary treatment between 2000 and 2014. SRS had been delivered as a single fraction of 12 Gy, and patients treated with FSRT had received 30 fractions of 1.8 Gy. To compare the effects of SRS and FSRT, we converted cochlear doses into EQD2. Primary outcomes were loss of functional hearing, Gardner Robertson (GR) classes I and II, and loss of baseline hearing class. These events were used in Kaplan Meier plots and Cox regression. We also calculated the rate of change in Pure Tone Average (PTA) in dB per month elapsed after radiation—a measure we use in linear regression—to assess the associations between the rate of change in PTA and age, pre-treatment hearing level, tumor size, dose scheme, cochlear dose, and time elapsed after treatment (time-to-first-audiogram).ResultsThe median follow-up was 36 months for 67 SRS patients and 63 months for 27 FSRT patients. Multivariate Cox regression and in linear regression both showed that the cochlear V90 was significantly associated with the progression of hearing loss. But although pre-treatment PTA correlated with rate of change in Cox regression, it did not correlate in linear regression. The time-to-first-audiogram was also significantly associated, indicating time dependency of the rate of change. None of the analysis showed a significant difference between dose schemes.ConclusionsWe found no significant difference between SRS and FSRT. As the deterioration in hearing after radiotherapy for vestibular schwannoma was associated with the cochlea V90, restricting the V90 may reduce progression of hearing loss. The association between loss of functional hearing and baseline PTA seems to be biased by the use of a categorized variable for hearing loss.

The Effect of Cochlear Dose on Hearing Preservation After Low-Dose Stereotactic Radiosurgery for Vestibular Schwannomas: A Systematic Review

“…48 This time lag created by using an arbitrary cut-off can deceptively associate pre-treatment PTA or GRC with the hearing outcome, especially if the follow-up period is not long enough. Linge et al 49 demonstrated this problem in their study, which analysed the hearing outcome in three different ways: functional hearing loss, loss of baseline GRC, and PTA increase per month. The pretreatment PTA and V90 of the cochlea were associated with hearing outcomes if the endpoint was functional hearing loss (GRC I and II) or loss of baseline GRC.…”

Clinical outcomes and toxicity of proton radiotherapy for vestibular schwannomas: a systematic review

“…Most reports included patients with shorter follow-up which may affect accurate assessment of tumor control and underestimate long-term sequelae. Hearing loss is dynamic over time and ideally assessed with minimum of 2-year follow-up, although longer follow-up may demonstrate further increase rate of hearing loss [29,44]. Statistics were overall well described but limited.…”

“…As the organs and tissues at risk include the cochlea, the vestibular organ, and the brainstem, reducing radiation dose is relevant. The risk of hearing loss after radiotherapy seems to be dependent on the dose administered to the cochlea, therefore a reduction of cochlear irradiation may result in better long-term hearing [22][23][24][25][26][27][28][29]. The consequences of low-dose brain irradiation are not well understood; however, it is possible that even small amounts of radiation have an impact on the healthy brain tissue [30,31].…”

Hearing Outcome After Linear Accelerator-Based Radiotherapy for Vestibular Schwannomas: A Retrospective Analysis of a Single Center

“…When hearing preservation is of patient’s utmost importance, radiation therapy with low dose to the cochlea should be considered. 20 - 22 However, whether this hearing preservation will be maintained in the long run is questionable as hearing clearly decreases after ten years of follow-up. 23 - 25 This decline is suggested to result from direct cochlear nerve compression by the tumor in the internal acoustic canal resulting in impedance of the auditory nerve.…”