3D quantitative assessment of response to fractionated stereotactic radiotherapy and single-session stereotactic radiosurgery of vestibular schwannoma

Objectives: To determine clinical outcome of patients with vestibular schwannoma (VS) after treatment with fractionated stereotactic radiotherapy (FSRT) and single-session stereotactic radiosurgery (SRS) by using 3D quantitative response assessment on MRI. Materials: This retrospective analysis included 162 patients who underwent radiation therapy for sporadic VS. Measurements on T1-weighted contrast-enhanced MRI (in 2-year post-therapy intervals: 0–2, 2–4, 4–6, 6–8, 8–10, 10–12 years) were taken for total tumour volume (TTV) and enhancing tumour volume (ETV) based on a semi-automated technique. Patients were considered non-responders (NRs) if they required subsequent microsurgical resection or developed radiological progression and tumour-related symptoms. Results: Median follow-up was 4.1 years (range: 0.4–12.0). TTV and ETV decreased for both the FSRT and SRS groups. However, only the FSRT group achieved significant tumour shrinkage (p < 0.015 for TTV, p < 0.005 for ETV over time). The 11 NRs showed proportionally greater TTV (median TTV pre-treatment: 0.61 cm³, 8–10 years after: 1.77 cm³) and ETV despite radiation therapy compared to responders (median TTV pre-treatment: 1.06 cm³; 10–12 years after: 0.81 cm³; p = 0.001). Conclusion: 3D quantification of VS showed a significant decrease in TTV and ETV on FSRT-treated patients only. NR had significantly greater TTV and ETV over time. Key Points: • Only FSRT not GK-treated patients showed significant tumour shrinkage over time. • Clinical non-responders showed significantly less tumour shrinkage when compared to responders. • 3D volumetric assessment of vestibular schwannoma shows advantages over unidimensional techniques.