Cochlear Dose Research Articles

Letter to the editor on "The cochlear dose and the age at radiotherapy predict severe hearing loss after passive scattering proton therapy and cisplatin in children with medulloblastoma".

Letter to the editor on "The cochlear dose and the age at radiotherapy predict severe hearing loss after passive scattering proton therapy and cisplatin in children with medulloblastoma".

Repeat stereotactic radiosurgery for progressive vestibular schwannomas after primary gamma knife radiosurgery

PurposeLimited data provides guidance on the management of vestibular schwannomas (VSs) that have progressed despite primary Gamma Knife radiosurgery (GKRS). The present article reports our long-term experience after repeat GKRS for VS with sustained progression after solely primary GKRS management.MethodsA retrospective review of 1997 patients managed between 1987 and 2023 was conducted. Eighteen patients had sustained tumor progression after primary GKRS and underwent repeat GKRS. The median repeat GKRS margin dose was 11 Gy (IQR: 11–12), the median tumor volume was 2.0 cc (IQR: 1.3–6.3), and the median cochlear dose in patients with preserved hearing was 3.9 Gy (IQR: 3-4.1). The median time between initial and repeat GKRS was 65 months (IQR: 38–118).ResultsThe median follow-up was 70 months (IQR: 23–101). After repeat GKRS, two patients had further tumor progression at 4 and 21 months and required partial resection of their tumors. The 10-year actuarial tumor control rate after repeat GKRS was 88%. Facial nerve function was preserved in 13 patients who had House-Brackmann grade 1 or 2 function at the time of repeat GKRS. Two patients with serviceable hearing preservation (Gardner-Robertson grade 1 or 2) at repeat GKRS retained that function afterwards. In patients with tinnitus, vestibular dysfunction, and trigeminal neuropathy, symptoms remained stable or improved for 16/16 patients, 12/15 patients, and 10/12 patients, respectively. One patient developed facial twitching in the absence of tumor growth 21 months after repeat GKRS.ConclusionsRepeat GKRS effectively controlled tumor growth and preserved cranial nerve outcomes in most patients whose VS had sustained progression after initial primary radiosurgery.

The cochlear dose and the age at radiotherapy predict severe hearing loss after passive scattering proton therapy and cisplatin in children with medulloblastoma.

Hearing loss (HL) is associated with worse neurocognitive outcomes among patients with medulloblastoma. We aimed to identify risk factors associated with severe HL and to evaluate the generalizability of a published HL calculator among patients treated with passive scattering proton therapy (PSPT) and cisplatin. We identified patients aged 3-21 years who were treated at our centers between 2007 and 2022. Audiograms were graded using the International Society of Pediatric Oncology (SIOP) Boston scale. Time to grades 3-4 HL was evaluated using Kaplan-Meier and multivariable Cox models to estimate hazard ratios and 95% confidence intervals (CI). Seventy-nine patients were treated with PSPT at a median age of 7.5 years (range: 3.1-21.1). The mean cochlear dose (Dmc) (±SD) was 31.5 ± 8.5 Gy, and the cumulative cisplatin dose was 295 ± 50 mg/m2. Fifty-nine patients (75%) received amifostine. Patients completed a median of 9 audiograms (range: 4-22) with a median audiogram follow-up of 49 months (range: 6-177). Twenty-seven patients (34%) had grades 3-4 HL. In adjusted Cox models, only higher Dmc (HR = 1.12, 95% CI:1.06-1.18) was associated with grades 3-4 HL. The predicted 3-year incidence of grades 3-4 HL was 40.0% (95% CI: 21.3-66.3) and 66.7% (95% CI: 35.4-93.7) for children with Dmc ≥36 Gy and age at radiotherapy ≥7 and <7 years, respectively (P = .042). It was 8.9% (95% CI: 2.3-31.6) and 15.6% (95% CI: 5.3-41.1) for children with Dmc <36 Gy and age at radiotherapy ≥7 and <7 years, respectively (P = .78). Children <7 years at radiotherapy with a Dmc ≥36 Gy are at higher risk for HL.

496 Impact of the Mean Cochlear Biologically Effective Dose on Hearing Preservation After Stereotactic Radiosurgery for Vestibular Schwannoma

INTRODUCTION: Stereotactic radiosurgery (SRS) is a useful alternative for small to medium size vestibular schwannoma (VSs). METHODS: This is a retrospective longitudinal single center study. Were analyzed 213 patients with useful baseline hearing. Risk of hearing decline was assessed for GR classes and pure tone average (PTA) loss. Mean follow-up period was 39 months (median 36, 6-84). RESULTS: Hearing decline (GR class) 3 years after SRS was associated with higher cochlear BEDGy2.47 mean (OR 1.39, p = 0.009). BEDGy2.47 mean was more relevant compared to BEDGy2.47 max (OR 1.13, p = 0.04). Mean (p = 0.91) and maximal (p = 0.66) cochlear doses were not statistically significant. Risk of PTA loss (continuous outcome, follow-up minus baseline) was significantly corelated with BEDGy2.47 mean at 24 (beta coefficient 1.55, p = 0.002) and 36 (beta coefficient 2.01, p = 0.004) months after SRS. Mean (p = 0.27) and maximal (p= 0.87) cochlear doses were not significant. Risk of PTA loss (&gt; 20 dB versus &lt;=20) was associated with higher BEDGy2.47 mean at 6 (OR 1.36, p= 0.002), 12 (OR 1.36, p = 0.007) and 36 (OR 1.37, p = 0.02) months. Mean cochlear dose was statistically significant only at 24 months. Risk of hearing decline at 36 months for BEDGy2.47 mean of 7-8, 10 and 12 Gy2.47 was 28%, 57% and 85%, respectively. CONCLUSIONS: Cochlear BEDGy2.47 mean is relevant for hearing decline after SRS and more relevant as compared with BEDGy2.47 max. Three years after SRS, this was sustained for all hearing decline evaluation modalities. Our data suggests BEDGy2.47 mean cut-off of &lt;= 8 Gy2.47 for better hearing preservation rates.

Hearing Outcomes from Gamma Knife Treatment for Intracanalicular Vestibular Schwannomas with Good Initial Hearing.

Background: The objective of this study was to describe the long-term hearing outcomes of gamma knife treatment for unilateral progressing vestibular schwannomas (VS) presenting with good initial hearing using audiologic data. Methods: A retrospective review was performed between 2010 and 2020 to select patients with progressing unilateral VS and good hearing (AAO-HNS class A) treated with stereotactic gamma knife surgery (GKS). Their audiograms were analyzed along with treatment metrics and patient data. Results: Hearing outcomes with a median follow-up of 5 years post-treatment showed statistically significant loss of serviceable hearing: 34.1% of patients maintained good hearing (AAO-HNS class A), and 56.1% maintained serviceable hearing (AAO-HNS class A and B). Non-hearing outcomes are favorable with excellent tumor control and low facial nerve morbidity. Conclusions: Hearing declines over time in intracanalicular VS treated with GKS, with a significant loss of serviceable hearing after 5 years. The mean cochlear dose and the presence of cochlear aperture obliteration by the tumor are the main statistically significant factors involved in the hearing outcomes.

Modeling the Risk of Hearing Loss From Radiation Therapy in Childhood Cancer Survivors: A PENTEC Comprehensive Review

The Pediatric Normal Tissue Effects in the Clinic (PENTEC) hearing loss (HL) task force reviewed investigations on cochlear radiation dose-response relationships and risk factors for developing HL. Evidence-based dose-response data are quantified to guide treatment planning. A systematic review of the literature was performed to correlate HL with cochlear dosimetry. HL was considered present if a threshold exceeded 20 dB at any frequency. Radiation dose, ototoxic chemotherapy exposure, hearing profile including frequency spectra, interval to HL, and age at radiation therapy (RT) were analyzed. Literature was systematically reviewed from 1970 to 2021. This resulted in 739 abstracts; 19 met inclusion for meta-analysis, and 4 included data amenable to statistical modeling. These 4 studies included 457 cochleas at risk in patients treated with RT without chemotherapy, and 398 cochlea treated with chemotherapy. The incidence and severity of cochlear HL from RT exposure alone is related to dose and age. Risk of HL was <5% in cochlea receiving a mean dose ≤35 Gy but increased to 30% at 50 Gy. HL risk ranged from 25% to 40% in children under the age of 5 years at diagnosis, declining to 10% in older children for any radiation dose. Probability of similar severe HL occurred at doses 18.3 Gy higher for children <3 versus >3 years of age. High-frequency HL was most common, with average onset occurring 3.6 years (range, 0.4-13.2 years) after RT. Exposure to platinum-based chemotherapies added to the rates of HL at a given cochlear dose level, with 300 mg/m2 shifting the dose response by 7 Gy. In children treated with RT alone, risk of HL was low for cochlear dose <35 Gy and rose when dose exceeded 35 Gy without clear RT dose dependence. High-frequency HL was most prevalent, but all frequencies were affected. Children younger than 5 years were at highest risk of developing HL, although independent effects of dose and age were not fully elucidated. Future reports with more granular data are needed to better delineate time to onset of HL and the effects of chemoradiotherapy.

Cochlear-optimized treatment planning in photon and proton radiosurgery for vestibular schwannoma patients

ObjectiveTo investigate the potential to reduce the cochlear dose with robotic photon radiosurgery or intensity-modulated proton therapy planning for vestibular schwannomas. Materials and MethodsClinically delivered photon radiosurgery treatment plans were compared to five cochlear-optimized plans: one photon and four proton plans (total of 120). A 1x12 Gy dose was prescribed. Photon plans were generated with Precision (Cyberknife, Accuray) with no PTV margin for set-up errors. Proton plans were generated using an in-house automated multi-criterial planning system with three or nine-beam arrangements, and applying 0 or 3 mm robustness for set-up errors during plan optimization and evaluation (and 3 % range robustness). The sample size was calculated based on a reduction of cochlear Dmean > 1.5 Gy(RBE) from the clinical plans, and resulted in 24 patients. ResultsCompared to the clinical photon plans, a reduction of cochlear Dmean > 1.5 Gy(RBE) could be achieved in 11/24 cochlear-optimized photon plans, 4/24 and 6/24 cochlear-optimized proton plans without set-up robustness for three and nine-beam arrangement, respectively, and in 0/24 proton plans with set-up robustness. The cochlea could best be spared in cases with a distance between tumor and cochlea. Using nine proton beams resulted in a reduced dose to most organs at risk. ConclusionCochlear dose reduction is possible in vestibular schwannoma radiosurgery while maintaining tumor coverage, especially when the tumor is not adjacent to the cochlea. With current set-up robustness, proton therapy is capable of providing lower dose to organs at risk located distant to the tumor, but not for organs adjacent to it. Consequently, photon plans provided better cochlear sparing than proton plans.

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

Stereotactic radiosurgery (SRS) is a useful alternative for small- to medium-sized vestibular schwannoma. To evaluate whether biologically effective dose (BED Gy2.47 ), calculated for mean (BED Gy2.47 mean) and maximal (BED Gy2.47 max) cochlear dose, is relevant for hearing preservation. This is a retrospective longitudinal single-center study. Were analyzed 213 patients with useful baseline hearing. Risk of hearing decline was assessed for Gardner-Robertson classes and pure tone average (PTA) loss. The mean follow-up period was 39 months (median 36, 6-84). Hearing decline (Gardner-Robertson class) 3 years after SRS was associated with higher cochlear BED Gy2.47 mean (odds ratio [OR] 1.39, P = .009). Moreover, BED Gy2.47 mean was more relevant as compared with BED Gy2.47 max (OR 1.13, P = .04). Risk of PTA loss (continuous outcome, follow-up minus baseline) was significantly corelated with BED Gy2.47 mean at 24 (beta coefficient 1.55, P = .002) and 36 (beta coefficient 2.01, P = .004) months after SRS. Risk of PTA loss (>20 dB vs ≤) was associated with higher BED Gy2.47 mean at 6 (OR 1.36, P = .002), 12 (OR 1.36, P = .007), and 36 (OR 1.37, P = .02) months. Risk of hearing decline at 36 months for the BED Gy2.47 mean of 7-8, 10, and 12 Gy 2.47 was 28%, 57%, and 85%, respectively. Cochlear BED Gy2.47 mean is relevant for hearing decline after SRS and more relevant as compared with BED Gy2.47 max. Three years after SRS, this was sustained for all hearing decline evaluation modalities. Our data suggest the BED Gy2.47 mean cut-off of ≤8 Gy 2.47 for better hearing preservation rates .

XRT-01. LONG-TERM HEARING LOSS IN CHILDREN WITH MEDULLOBLASTOMA AFTER PROTON IRRADIATION AND CHEMOTHERAPY

Abstract PURPOSE To evaluate the incidence and risk factors for hearing loss (HL) among children with medulloblastoma treated with proton irradiation and cisplatin. METHODS We identified children with medulloblastoma ≥3 years of age treated at Texas Children’s Hospital between 2007-2022. Audiograms were graded using the International Society of Pediatric Oncology-Boston scale (SIOP-Boston). Time to grade ≥3 HL was evaluated using Kaplan-Meier and multivariable Cox models to estimate hazard ratios (HR) and 95% confidence intervals (CI). RESULTS Seventy-eight patients (65.4% male) were treated with craniospinal irradiation (CSI) at a median age of 7.6 years (range: 3-21). The mean cochlear irradiation dose was 31.5±9 Gy, and the cumulative cisplatin dose was 295±50 mg/m2. Fifty-six patients (72%) received amifostine. Patients completed a median of 9 audiograms (range: 4-22) with a median audiogram follow-up of 49 months (range: 3-177). Grade ≥3 HL was documented in 25 patients (32%). In adjusted Cox models, mean cochlear dose (HR=1.12, 95% CI: 1.06-1.18) and the age at CSI (HR=0.81, 95% CI: 0.68-0.98) were associated with grade ≥3 HL. Among children who received irradiation after or at 7 years of age, the estimated probability of grade ≥3 HL at three years post-CSI was 12.6% (95% CI: 4.1-34.6) in children exposed to &amp;lt;36 Gy cochlear irradiation and 35.6% (95% CI: 17.4-63.6) in children exposed to &amp;gt;36 Gy cochlear irradiation. Among children who received irradiation before 7 years of age, the estimated probability of grade ≥3 HL at three years post-CSI was 16.5% (95% CI: 5.6-43) in children exposed to &amp;lt;36 Gy cochlear radiation and 66.7% (95% CI: 35.4-93.7) in children exposed to &amp;gt;36 Gy cochlear irradiation. CONCLUSION Long-term follow-up shows that children who received a cochlear dose ≥36 Gy before 7 years of age are at higher risk for HL, regardless of the amifostine and the cisplatin dose.

Impact of Cochlear Dose on Hearing Preservation Following Stereotactic Radiosurgery in Treatment of Vestibular Schwannomas: A Multi-Center Study

Stereotactic radiosurgery (SRS) is a well-established treatment for vestibular schwannomas (VS). Hearing loss remains a main morbidity of VS and its treatments, including SRS. The effects of radiation parameters of SRS on hearing remain unknown. The goal of this study is to determine the effect of tumor volume, patient demographics, pretreatment hearing status, cochlear radiation dose, total tumor radiation dose, fractionation, and other radiotherapy parameters on hearing deterioration. Multicenter retrospective analysis of 611 patients who underwent SRS for VS from 1990-2020 and had pre- and post-treatment audiograms. Pure tone averages (PTAs) increased and word recognition scores (WRSs) decreased in treated ears at 12-60 months while remaining stable in untreated ears. Higher baseline PTA, higher tumor radiation dose, higher maximum cochlear dose, and usage of single fraction resulted in higher post radiation PTA; WRS was only predicted by baseline WRS and age. Higher baseline PTA, single fraction treatment, higher tumor radiation dose, and higher maximum cochlear dose resulted in a faster deterioration in PTA. Below a maximum cochlear dose of 3 Gy, there were no statistically significant changes in PTA or WRS. Decline of hearing at one year in VS patients after SRS is directly related to maximum cochlear dose, single versus 3-fraction treatment, total tumor radiation dose, and baseline hearing level. The maximum safe cochlear dose for hearingtbrowd preservation at one year is 3 Gy, and the use of 3 fractions instead of one fraction was better at preserving hearing.

Radiation dose to the cochlea and its association with sensorineural hearing loss in head and neck cancer-A prospective study

AimTo determine the effect of cochlear dose on sensorineural hearing loss in patients with head and neck cancer treated by radiotherapy and chemoradiotherapy. Materials and methodA two-year longitudinal study was conducted on 130 subjects with various head and neck malignancies who were receiving radiotherapy or chemoradiation. 56 patients received only radiotherapy while 74 patients received concurrent chemoradiation five days a week at a dose of 66–70 Gy. They were categorized as having a radiation dose to the cochlea of <35 Gy, <45 Gy or >45 Gy. Pre- and post-therapy audiological evaluation was done using a Pure-tone audiogram, distortion product otoacoustic emission, and impedence. Hearing thresholds were measured at frequencies up to 16,000 Hz. ResultsOut of 130 patients 56 received RT alone and 74 received CTRT. There was statistically significant (p value <0.005) difference in Pure-tone audiometry assessment in both the RT and CTRT groups between subjects who received more than and <45 Gy of radiation to the cochlea. There was no significant difference in distortion product otoacoustic emission assessment between patients who received >45 Gy and <45 Gy radiation to the cochlea. Comparison between subjects who received radiation dose of <35 Gy and >45 Gy revealed significant results in the degree of hearing loss (p value <0.005). ConclusionWe observed that patients who received >45 Gy of radiation had more sensorineural hearing loss compared to patients who received <45 Gy. A cochlear dose of <35 Gy is associated with significantly lower hearing loss compared to higher doses. We would like to conclude by emphasizing the importance of regular audiological assessments prior to and post radiotherapy and chemoradiotherapy, with regular follow-ups encouraged over a longer period to improve the quality of life in patients with head and neck malignancy.

Outcomes and Prognostic Factors in the Treatment of Intracanalicular Vestibular Schwannomas Using Gamma Knife Stereotactic Radiation.

No gold standard has been developed for the therapy of intracanalicular vestibular schwannomas (IVS). Options for treatment include a conservative approach, microsurgery, or radiosurgery. Although the efficacy of these treatment has been well-documented, little is known about the determinants of outcome in IVSs following radiosurgery. Therefore, we examined the results in relation to age, gender, tumor volume, distance to fundus, microcyst existence, and radiosensitivity in this group. In addition, we investigated possible predictors of facial nerve function and hearing preservation. Ninety-four patients with unilateral IVS were included in the evaluation (52 women and 42 males). The patients were separated into younger and older age groups based on their median age (55 years). The median IVS volume was 138 mm3, microcysts were identified in 16 tumors, and 63 tumors were adjacent to the fundus. The data were analyzed using Statistica software package ver. 13.3. At final follow-up, a statistically significant decrease in tumor volume and no statistically significant decline in hearing were noted, but no differences between age groups were found. The sex had no effect on overall tumor growth control, facial nerve preservation, or hearing preservation. Localization of IVS close to the fundus and the presence of tumor microcysts had no effect on the control of tumor growth, preservation of hearing, and sparing of facial nerve following radiosurgery. Cochlear dose had no influence on hearing preservation. Higher tumor volume was associated with its pseudoprogression during early follow-up and a greater risk of hearing loss. Age, sex, tumor volume, proximity to the fundus, and the existence of a microcyst were not predictive of radiosensitivity nor preservation of facial nerve function and hearing, based on the findings. There was no effect of cochlear dose on hearing. Initial greater tumor volume was associated with an increased probability of tumor pseudoprogression.

Effects of Chemoradiation Therapy on Hearing in Patients with Malignancy of Head and Neck.

To study effects of chemoradiation therapy on hearing in patients with malignancy of head and neck. Patients receiving drugs other than cisplatin as well as those with any otology-related pathology or abnormalities were excluded from the study. Patients with primary biopsy-proven malignancy of the Nasopharynx, Oropharynx, Paranasal Sinuses, Oral Cavity, and Parotid with chemoradiation by cisplatin and different radiation modalities were all eligible. Areas of interest and OARs are indicated on CT images. All patients' hearing was assessed using pure tone audiometry at the beginning of treatment, at its conclusion, and six months later. Variations in pure tone thresholds from baseline and CTCAE - Common Terminology Criteria for Adverse Events grading are related to cochlear dose. The study involves 75 patients. At cochlear dosage levels of more than 40Gy, significant SNHL (>10 dB loss) is seen. Absolute PTA threshold values do not statistically differ from baseline to completion at any frequency. For 4000 and 8000Hz, the absolute PTA threshold values differed from baseline to follow-up, but only for 8000Hz was the difference statistically significant after six months of follow-up. Following treatment, 64% of patients had grade I CTCAE scoring and 16% and 12%, respectively, had otitis media with effusion and Eustachian tube dysfunction. The inner ear may be harmed in patients receiving radiation to the head and neck. Radiation-induced SNHL typically goes unreported in routine clinical practise because of its long-term nature. In the group of head and neck tumours with high-risk locations, nearly 90% of patients with SNHL were affected. Therefore, it's critical to reduce cochlear dosage in these patient populations. More investigation is needed to distinguish between cochlear and retro-cochlear types of sensorineural hearing loss.

214 Impact of Cochlear Dose on Hearing Preservation Following Stereotactic Radiosurgery in Treatment of Vestibular Schwannomas: A Multi-Center Study

INTRODUCTION: Stereotactic radiosurgery (SRS) is a well-established treatment option for patients with vestibular schwannomas (VS). Hearing loss remains one of the main morbidities of VS and its treatments, including SRS. Effects of radiation parameters of SRS on hearing remains largely unknown. METHODS: Multicenter retrospective analysis of 611 patients who underwent SRS for VS from 1990 to 2020 and had pre- and post-treatment audiograms. RESULTS: Pure tone averages (PTA)s increased and word recognition scores (WRS)s decreased in the treated ears at 12 - 60 months while it remained stable in the untreated ears. Higher baseline PTA, higher tumor radiation dose, higher maximum cochlear dose, and usage of single fraction resulted in higher post radiation PTA; WRS was only predicted by baseline WRS and age. Of these parameters, higher baseline PTA, single fraction treatment, higher tumor radiation dose, and higher maximum cochlear dose resulted in a faster deterioration in PTA. Below a maximum cochlear dose of 3 Gy, there were no statistically significant changes in PTA or WRS. CONCLUSIONS: Decline of hearing at 1 year in VS patients after SRS is directly related to maximum cochlear dose, single versus 3-fraction treatment, total tumor radiation dose, and baseline hearing level. The maximum safe cochlear dose for hearing preservation at 1 year is 3 Gy, and the use of 3 fractions instead of 1 fraction was better at preserving hearing.

509 Modern Hearing Preservation Outcomes After Vestibular Schwannoma Stereotactic Radiosurgery

INTRODUCTION: For patients with vestibular schwannoma (VS), stereotactic radiosurgery (SRS) has proven effective in controlling tumor growth, while hearing preservation remains a key goal. METHODS: During the years 2013-2018, 353 patients underwent Gamma-knife surgery for VS at our institution. We followed 175 patients with pre-SRS serviceable hearing (Gardner-Robertson Score, GR 1 and 2). Volumetric and dosimetry data were collected, including Biological Effective Dose (BED), integral doses (ID) of total and intra-canalicular (IC) tumor components and hearing outcomes. RESULTS: Mean age was 56 years, 74 (42%) had baseline GR of 2, and mean cochlear dose was 3.5 Gy. Time to serviceable hearing loss (GR 3-4) was 38 months (95% CI, 26-46), with 77% and 62% hearing preservation in the 1st and 2nd years. Patients optimal for best hearing outcomes were younger than 58 with baseline GR of 1, free canal space 0.041cc (diameter of 4.5 mm) and mean cochlear dose &lt;3.1 Gy. For such patients, hearing preservation rates were 92% by 12 months and 81% by 2 years, staying stable for &gt;5 years post-SRS, significantly higher than the rest of the population. CONCLUSIONS: Hearing preservation after SRS for VS patients with serviceable hearing is correlated to the specific baseline GR score (1 or 2), age, cochlear dose and BED. Increased tumor-free canal space correlates with better outcomes. The most durable hearing preservation correlates with factors commonly associated with smaller tumors away from the cochlea.

Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

BackgroundStereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.MethodsEligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.ResultsEighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.ConclusionLINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.

Factors Affecting Permanent Sensorineural Hearing Loss and Bone Conduction in Patients After Receiving Radiotherapy to the Head and Neck Region.

This study aimed to investigate the factors affecting permanent sensorineural hearing loss (SNHL) and causing changes in bone conduction (BC) thresholds over time in patients after receiving radiotherapy (RT) or chemoradiotherapy (CRT) to the head and neck region. A total of 63 patients with irradiated HNC that were admitted to the Radiation Oncology Department between 2011 and 2018 were included in the study. All patients were assessed with pure tone audiometry at eight different time points (first before RT and last five years after completion of RT). A chi-square test was used to analyze the variables that affected permanent SNHL occurrence. Repeated measure analysis of variance was conducted to investigate the factors affecting change in the BC threshold at pure-tone average (0.5-2 kHz) and the air conduction (AC) threshold at 4 and 6 kHz frequencies over time. Median follow-up was 52 months (range, 12-110 months). SNHL was found in 18 (14%) of the 126 ears. According to the receiver operating characteristic analysis, the cut-off values of cochlear Dmean and Dmax radiation doses were 40 Gy [p=0.017, area under the curve (AUC): 0.676] and 45 Gy (p=0.008, AUC: 0.695). Dmean (≤40 Gy vs. >40 Gy) and Dmax (≤45 Gy vs. >45 Gy) cochlear doses and age (≤40 vs. >40 years) were determined as factors affecting SNHL in the chi-square test. Repeated measures showed that BC thresholds between 0.5-2 kHz and AC thresholds at 4 and 6 kHz increased over time. Age (≤40 vs. >40 years), treatment of head and neck cancer (RT vs. CRT), cisplatin use, and Dmean (≤40 Gy vs. >40 Gy) and Dmax cochlear dose (≤45 Gy vs. >45 Gy) were important factors affecting the course of BC threshold over time. Dmean and Dmax cochlear doses and age were found to be associated with permanent SNHL. Conduction thresholds worsened over time at all frequencies, and this trend was affected by cochlear doses, age, CRT, and cisplatin use.

RADT-38. INCIDENCE OF HEARING IMPAIRMENT AFTER DEFINITIVE PROTON BEAM THERAPY FOR MALIGNANCIES OF THE BRAIN AND BASE OF SKULL

Abstract AIM Aim of the project is to report the incidence of moderate/severe (G ≥ 3) long-term hearing impairment (HI) and to identify risk factors in patients treated for malignancies of the brain and base of skull with definitive Proton Beam Therapy (PBT) within the Proton Overseas Programme (POP). METHODS Clinical and treatment-related data from patients’ files stored in a national database and curated by a dedicated outcomes unit were extracted and analysed. Clinical toxicity data from the POP were graded as per Common Terminology Criteria for Adverse Events (CTCAE 4.0). Dosimetric data (Dmean to the cochlear structures) were extracted from the Treatment Planning System Proknow. For the purpose of this analysis, patients with radical definitive PBT only were selected. RESULTS Between 2008 - 2018, 229 UK patients received radical PBT overseas for Craniopharyngioma (104 patients;45.4%), Chordoma (60; 26.2%), Chondrosarcoma (53;23.1%), Meningioma (7;3%), Pituitary Adenoma (5;2.1%). Median age was 17 years (1-77). Median prescription dose was 55.8 Gy (45-75.8). Median dose to the Left and Right cochleas were 14.18 Gy (0-85.15) and 12.55 Gy (0-77.50), respectively. Eight patients developed G ≥ 3 HI (3.5%). Of those, 7 had received dose escalated treatments for radioresistant tumours (chordomas or condrosarcomas). In 4/8, the HI was bilateral. The median cochlear dose for the structures who developed G ≥ 3 HI was 48.99 Gy (10-76.87). CONCLUSIONS Incidence of G ≥ 3 HI in this patient population compares with historical cohorts, and, as expected, is higher in patients who receive dose escalated treatments for radioresistant tumours of the base of skull. Median dose in those who developed HI supports the use of dose constraints used in the clinical PBT practice.

Multi-Center Quality of Life Outcomes for Patients with Acoustic Neuromas Treated with a Non-Invasive Stereotactic Radiosurgery Instrument and Linear Accelerator-Based Radiosurgery

<h3>Purpose/Objective(s)</h3> Prior studies have reported favorable local control for patients treated with Gamma Knife (GK) or linear accelerator (LINAC)-based radiosurgery (SRS); however, direct comparison of detailed patient-reported quality of life (QOL) outcomes are lacking. This multi-center retrospective review assessed for differences in QOL outcomes and toxicity profiles after radiotherapy for acoustic neuromas in patients treated with GK and LINAC-based radiosurgery. <h3>Materials/Methods</h3> In this multi-center single institution analysis, we retrospectively reviewed acoustic neuroma cases treated with either GK or LINAC-based SRS between 2008-2017. We compared pre- and post- treatment clinical outcomes including new development of tinnitus, vertigo, gait disturbance, facial palsy, hydrocephalus and audiometric data. We also collected radiographic and dosimetric information including tumor size and dose to cochlea. Descriptive statistics were performed and χ² was utilized to assess for intergroup differences in clinicoradiographic or dosimetric differences. Univariate and multivariate multinomial logistic regression analyses were performed with backward selection at alpha of 0.2 to assess for statistically significant associations with the development of the clinical endpoints described above. <h3>Results</h3> A total of 85 patients were included in our review, 36 in the GK group and 49 in the LINAC-SRS group. 39 patients were male (45.9%) and 46 female (54.1%), 45 were left-sided tumors (52.9%) and 40 right-sided tumors (47.1%). All patients were treated with single-fraction SRS, with a prescription of 12.5 Gy for GK and 12 Gy for LINAC-based SRS. Median follow up was 25 months (median 21 months in GK group, 26 months in LINAC group). On multivariate analysis, there was no significant difference in the development of post-treatment tinnitus, vertigo, gait disturbance, facial palsy, hydrocephalus, change in Gardner Robertson Grade, or change in hearing between the GK and LINAC treatment groups (p> 0.05). Similarly, multivariate analysis did not show tumor size or cochlear dose to be associated with development of specific toxicities between treatment modalities (p>0.05). <h3>Conclusion</h3> This multi-center retrospective review found no significant differences in patient-reported QOL outcomes for patients treated with either Gamma Knife or LINAC-based radiosurgery for acoustic neuromas. This study adds to the body of evidence that both modalities are feasible approaches with similar toxicity profiles for the treatment of acoustic neuromas, and patients can be counselled as such.

Matched Comparison of Hearing Outcomes in Patients With Vestibular Schwannoma Treated With Stereotactic Radiosurgery or Observation.

Previous studies comparing hearing outcomes in patients managed with stereotactic radiosurgery (SRS) and a watch-and-wait strategy were limited by small sample sizes that prevented controlling for potential confounders, including initial hearing status, tumor size, and age. To compare hearing outcomes for patients with vestibular schwannomas (VS) managed with observation and SRS while controlling for confounders with propensity score matching. Propensity score matching was used to compare 198 patients with unilateral VS with initial serviceable hearing (99 treated with SRS and 99 managed with observation alone) and 116 with initial class A hearing (58 managed with SRS and 58 with observation), matched by initial hearing status, tumor volume, age, and sex. Kaplan-Meier survival methods were used to compare risk of losing class A and serviceable hearing. Between patients with VS managed with SRS or observation alone, there was no significant difference in loss of class A hearing (median time 27.2 months, 95% CI 16.8-43.4, and 29.2 months, 95% CI 20.4-62.5, P = .88) or serviceable hearing (median time 37.7 months, 95% CI 25.7-58.4, and 48.8 months, 95% CI 38.4-86.3, P = .18). For SRS patients, increasing mean cochlear dose was not related to loss of class A hearing (hazard ratio 1.3, P = .17) but was associated with increasing risk of serviceable hearing loss (hazard ratio of 1.5 per increase in Gy, P = .017). When controlling for potential confounders, there was no significant difference in loss of class A or serviceable hearing between patients managed with SRS or with observation alone.