Volumetric and Linear Imaging Response After Stereotactic Radiotherapy for Vestibular Schwannoma

Area of Science:

• Neurosurgery
• Radiation Oncology
• Oncology

Background:

• Vestibular schwannomas (VS) are benign tumors affecting the vestibulocochlear nerve.
• Increased MRI detection of small VS shifts management towards functional preservation.
• Stereotactic radiotherapy (SRT) offers high tumor control, but progression criteria and regimen-specific outcomes need further study.

Purpose of the Study:

• To evaluate tumor control and progression criteria after SRT for VS.
• To compare outcomes across single-fraction stereotactic radiosurgery (SRS), hypofractionated stereotactic radiotherapy (HFSRT), and fractionated stereotactic radiotherapy (FSRT).
• To identify factors predicting tumor progression and clinical worsening.

Main Methods:

• Retrospective review of 143 adult VS patients treated with SRT (2013-2022).
• Tumor control assessed volumetrically (≥20% increase) and linearly (MLD ≥2 mm) at 12 months, 24 months, and 5 years.
• Analysis of baseline features, symptoms, and treatment variables for associations with outcomes.

Main Results:

• Volumetric progression declined over time (22% at 12m, 15% at 24m, 17% at 5y), while linear progression remained stable (14% at 12m, 13% at 24m, 12% at 5y).
• Volumetric progression correlated with clinical worsening, particularly hearing decline (p<0.05).
• Outcomes were similar across SRS, HFSRT, and FSRT at 5 years, with SRS showing earlier pseudoprogression.

Conclusions:

• SRT provides durable VS control with minimal need for salvage interventions.
• The 20% volumetric criterion is superior to the 2 mm MLD threshold for assessing tumor progression.
• Annual MRI is generally sufficient post-treatment, with earlier progression observed within 24 months.