S949
Clinical - Non-malignant & functional radiotherapy
ESTRO 2026
Purpose/Objective: Stereotactic radiosurgery (SRS), delivered as a single- dose or hypofractionated regimen (fSRS), is an effective and low-toxicity treatment for vestibular schwannomas (VS), used both as primary and adjuvant therapy. Beyond tumor control, hearing preservation has become a critical determinant of patient quality of life. However, long-term data on hearing preservation after SRS or fSRS remain limited. This study aimed to evaluate hearing preservation outcomes following stereotactic radiosurgery for VS. Material/Methods: We retrospectively analyzed a cohort of MRI-confirmed VS patients treated with radiosurgery between 2021 and 2025. Treatment consisted of 12–13 Gy single- dose SRS or 25–30 Gy in five fractions (fSRS), with hypofractionation reserved for larger or higher Koos grade tumors. Hearing preservation was defined as pure-tone audiometry (PTA) ≤ 50 dB or Gardner– Robertson scale (GR) ≤ 2, and neurological toxicities were recorded. Results: Twenty-two patients were included (median age 53 years), with 4 treated with SRS and 18 with fSRS. Median follow-up was 29 months. Ten patients had prior partial tumor resection. Median tumor volume was 2.80 cm ³ ; 1.60 cm ³ for single-fraction and 3.50 cm ³ for hypofractionated treatments. Overall, 81.8% (n=18) were Koos Grade 3 or 4. The median mean cochlear dose was 11.7 Gy (range 3.4–26.9), higher in the hypofractionated group (12.5 Gy vs 10.2 Gy). Median maximum dose was 20.2 Gy (range 5.5–31.7 Gy), also higher with fSRS. Median D100% was 7.4 Gy (range 1.3–20.8 Gy).At baseline, median PTA was 35.5 dB (range 12–70), with 9 patients (40.9%) having serviceable hearing (2 SRS, 7 fSRS). Serviceable hearing remained stable at 77.8% (n=7), despite a median PTA increase of 6,20 dB and a median speech discrimination decrease of 10%. Usable hearing preservation was 100% (2/2) in the SRS group and 71.4% (5/7) in the fSRS group. Most patients reported no changes in facial or trigeminal nerve function or balance, with only one case of new-onset trigeminal hypoesthesia. Conclusion: Our results are consistent with the literature, showing hearing preservation rates around 70%. SRS successfully maintained serviceable hearing in most patients with VS, with minimal impact on facial, trigeminal, and balance functions. These findings highlight the importance of comprehensive audiological assessment as part of both pre- and post- radiosurgery protocols to optimize patient outcomes. References: Marchetti M, Pinzi V, Gemma M, Cuccarini V, Pascuzzo R, Cane I, Romeo A, Morlino S, De Martin E, Fariselli L. Hypofractionated versus single-session radiosurgery
to preserve hearing in patients affected by sporadic vestibular schwannoma: the ACOUNEU randomized clinical trial. Int J Radiat Oncol Biol Phys. 2025. Keywords: Schwannomas; SRS; Hearing preservation
Digital Poster Highlight 2871 Curative proton therapy for hyperthyroidism: an exploratory study of the optimal dose and patients’ selection criteria Taro Murai 1 , Kazuki Matsumoto 2 , Shunsuke Suzuki 2 , Takayuki Yagihashi 2 , Sachika Shiraishi 1 , Shintaro Shiba 1 , Koichi Tokuuye 1 1 Radiation oncology, Shonan Kamakura General Hospital, Kamakura, Japan. 2 Medical Physics, Shonan Kamakura General Hospital, Kamakura, Japan
Purpose/Objective: Surgical resection is considered the standard
treatment for hyperthyroidism caused by large goiters; however, it is associated with significant risks such as fatal bleeding and palsy. Although radiation therapy can reduce thyroid hormone production, concerns about secondary malignancies remain. Proton therapy (PT) offers superior dose distribution, which may mitigate this risk. This study aimed to determine the optimal radiation dose and patient selection criteria for PT by simulating disease control probability (DCP) and the lifetime attributable risk (LAR) per 10,000 patients for future trials of PT for hyperthyroidism. Material/Methods: PT plans were generated using pre-thyroidectomy CT images, with the CTV defined as the thyroid. Physical dose distributions were converted to equivalent doses in 2 Gy fractions, and the Lyman–Kutcher–Burman model was employed to calculate DCP and normal tissue toxicity. LAR was calculated using Schneider’s formula. Given the influence of age on LAR, simulations were conducted across a patient age range from 0 to 100 years. Prescribed doses were categorized into four levels: 17.4, 20.7, 23.4, or 26.1 GyE/3 fractions (3-fraction group); 21, 25, 29, or 32 GyE/5 fractions (5-fraction group); and 27, 33, 38, or 42 GyE/10 fractions (10-fraction group). An acceptable treatment scenario was defined as achieving a DCP ≥ 80% while maintaining LAR ≤ 300 per 10,000. Results: Ten patients (7 females, 3 males) were included, with a mean thyroid volume of 31.5 cc. A DCP exceeding 80% was observed only at the highest dose levels within each fractionation schedule: 88% for 26.1 GyE/3 fr, 86% for 32 GyE/5 fr, and 87% for 42 GyE/10 fr, respectively. The estimated probabilities of laryngeal edema and esophageal stenosis were below 2%. LAR decreased exponentially with increasing age. Among females receiving 26.1 GyE/3 fr, median LARs were
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