2026 Proffered Presentations
S197: IMPACT OF PRE-TREATMENT GROWTH RATE AND RADIOSURGERY APPROACH ON STEREOTACTIC RADIOSURGERY OUTCOMES IN VESTIBULAR SCHWANNOMA
Pranav Bingi, BS1; Khoa Nguyen, BS1; Kalena Liu, BS1; Anika Walia, BS1; Wenyin Shi, MD2; Jacob Hunter, MD1; 1Thomas Jefferson University, Department of Otolaryngology; 2Thomas Jefferson University, Department of Radiation Oncology
Introduction: Vestibular Schwannomas (VS) are often treated by stereotactic radiosurgery (SRS), with single dose (sSRS) and fractionated therapy (fSRS) being two key modalities. While SRS is known to be effective at tumor control, there is limited understanding of how pre-treatment tumor growth impacts SRS outcomes, especially between different radiation modalities.
Methods: A single-institutional retrospective chart review was conducted for VS patients treated with SRS between 2001 and 2023. Patient demographics, SRS modality, and serial MRI sizes were collected. Patients with neurofibromatosis 2, follow-up <12 months, and those without imaging within 6 months of treatment were excluded.
Patients were stratified using two approaches: pre-treatment tumor growth (growing= ≥2.5 mm/year vs stable= <2.5 mm/year) and radiation approach (single dose vs fractionated). Analyses, including bivariate analysis, across both stratifications, evaluated tumor size change, tumor growth (≥2 mm increase in greatest linear dimension), pseudo-progression (≥2 mm increase followed by regression), and post-treatment growth rate over time.
Results: Of 103 patients who met inclusion criteria, 59.2% (61/103) were classified as stable and 40.8% were (42/103) classified as growing prior to SRS. Overall, 43.6% (45/103) received single-dose SRS and 58 (56.4%) received fSRS. Baseline tumor sizes did not differ across all comparisons: between sSRS and fSRS within stable (1.56 vs 1.58 cm, p=0.94) or growing tumors (1.92 vs 1.52 cm, p=0.21), and between stable and growing tumors in sSRS (1.56 vs 1.92 cm, p=0.40) or fSRS groups (1.58 vs 1.52 cm, p=0.63).
When stratified by pre-treatment growth status, stable tumors showed greater size reduction with sSRS (n=27, -1.14 ± 4.21 mm) compared to fSRS (n=34, 0.58 ± 4.12 mm; p=0.03). This relationship held for growing tumors, with size change of -6.54 ± 9.89 mm in sSRS patients (n=18) and -1.37 ± 4.01 mm in fSRS patients (n=24; p=0.04).
When stratified by radiation type, sSRS exhibited greater size reduction in growing (n=18, -6.54 ± 9.89 mm) compared to stable tumors (n=27, -1.14 ± 4.21 mm; p=0.034). No significant difference in size reduction was observed in patients undergoing fSRS with stable (n=34, 0.58 ± 4.12mm) and growing tumors (n=24, mean= -1.37 ± 4.01 mm; p=0.05).
On bivariate analysis, tumor size reduction in growing tumors (-3.59 ± 7.51 mm) and tumors treated with sSRS (-3.3 ± 7.44 mm) were significantly greater (p=0.008; p=0.006) compared to stable (-0.19 ± 4.21 mm) and fractionated (-0.23 ± 4.15 mm) tumors, respectively. Post-treatment growth rates for sSRS (-1.64 ± 4.17 mm/year) were significantly lower than fSRS (-0.26 ± 2.42 mm/year; p=0.0266), and fSRS showed higher rates of post-treatment enlargement (fSRS n=11, single-dose n=1; p=0.01).
Post-treatment growth and pseudo-progression did not differ significantly across groups.
Conclusion: sSRS was associated with significantly greater tumor size reduction, lower post-treatment growth rates, and lower post-treatment enlargement than fSRS. Additionally, growing tumors displayed significantly greater size reduction overall. Results suggest tumor growth and treatment modality should be considered to optimize VS treatment.
Figure 1: Stratification structure: 1) pre-treatment growth, 2) SRS modality
Figure 2: Stratification structure: 1) SRS modality, 2) pre-treatment growth