2073 - Robotic-Arm Linear Accelerator Radiotherapy for Vestibular Schwannomas: A Single-Institution Experience
Presenter(s)
B. Goc1, I. Debosz-Suwinska2, A. Roch-Zniszczol2, A. Misiorowska-Golosz2, D. Gräupner2, M. Stapór-Fudzinska3, A. Cortez4, M. Zydowicz5,6, J. Wydmanski7, and S. Blamek7; 1Department of Radiotherapy, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch, 44-102 Gliwice, Poland, Gliwice, Poland, 2Department of Radiotherapy, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, Poland, 3Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice, Poland, 4Maria Sklodowska-Curie National Institute of Oncology, Gliwice, Poland, 5Department of Biostatistics and Bioinformatics, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch, 44-102 Gliwice, Poland, Gliwice, Poland, 6Digital Medicine Center, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch, 44-102 Gliwice, Poland, Gliwice, Poland, 7Department of Radiotherapy, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch., Gliwice, Poland
Purpose/Objective(s): Radiosurgery and stereotactic fractionated radiotherapy are highly effective modalities for achieving local control in vestibular schwannomas. While a substantial part of the existing literature focuses on the Gamma Knife system, based on our institutional data we analyzed a cohort of patients treated with the robotic-arm linear accelerator, aiming to evaluate both the efficacy and safety of this approach. Additionally, we sought to investigate potential clinical and radiobiological parameters affecting treatment outcomes to establish predictive or prognostic indicators.
Materials/Methods: We retrospectively analyzed an initial cohort of 310 vestibular schwannomas treated in 262 patients at our institution with the robotic radiotherapy system between 2013 and 2020. To ensure the homogeneity of the study population, patients diagnosed with neurofibromatosis type 2 (NF2) were excluded from the efficacy analysis as well as those with a follow-up of less than 6 months. Treatment schedules depended on tumor volume: smaller lesions predominantly received single-fraction radiosurgery (12 Gy), whereas larger tumors were treated with hypofractionated radiotherapy (typically 16 Gy or 18 Gy delivered in 2 or 3 fractions, respectively). Local tumor control (LC) was defined as the absence of both baseline symptom progression and tumor enlargement on follow-up imaging. In order to assess predictors of vestibular schwannomas progression a univariable and multivariable logistic regression analysis was performed with reduction in a stepwise manner. A two-sided P value = 0.05 was considered statistically significant.
Results: The final efficacy analysis included 236 evaluable vestibular schwannomas, which included 34 cases treated for progression following prior surgical resection. Over half of the tumors (54%) were Koos grade I or II. The median follow-up was 32 months (range: 6-144) with a median prescribed dose of 16 Gy. Actuarial rates of clinical symptom control were 93% and 88% at 3 and 5 years, respectively. Correspondingly, radiological local control (absence of tumor enlargement) was achieved in 94% and 88% of cases at 3 and 5 years. Acute toxicity was limited, occurring in 8 patients as transient exacerbation of headaches, while post-treatment hearing deterioration was observed in 11 patients. In multivariable logistic regression analysis pre-existing tinnitus was significantly associated with clinical progression, identifying it as a potential clinical prognostic factor.
Conclusion: Robotic-arm stereotactic radiotherapy is a safe and highly effective modality, yielding over 90% long-term tumor control for vestibular schwannomas. This analysis provides a strong rationale for expanding the cohort to further elucidate the specific predictors of treatment failure and potential toxicity.