RADT-07. PSEUDO-PROGRESSION OF VESTIBULAR SCHWANNOMA AFTER GAMMA KNIFE RADIOSURGERY

Abstract OBJECTIVE To assess the incidence and clinical significance of transient volume enlargement followed by stabilization or regression (pseudo-progression) in vestibular schwannoma (VS) after Gamma Knife radiosurgery (GKRS). METHODS A retrospective review was conducted on 143 patients with sporadic VS who underwent GKRS and were followed for a minimum of 24 months. GKRS was performed as a primary treatment in 86 patients (60%) and as adjuvant therapy following surgery in 57 (40%). The mean tumor volume at treatment was 2.1 cc (range, 0.004–12.567), and the median marginal dose was 12 Gy (range, 11–14). Pseudo-progression was defined as a tumor volume increase of >20% post-GKRS, followed by regression to <120% of the original volume. RESULTS Pseudo-progression occurred in 57 patients (40%) during a median follow-up of 62.2 months (range, 24.1–194.6). The median time to pseudo-progression was 6.1 months, and regression was observed at a median of 18 months. Of the 57 cases, 53 showed regression to below the original volume, and 4 stabilized at 100–120% of the baseline. Pre-existing intra-tumoral necrosis and age over 60 years were significantly associated with pseudo-progression in both univariate and multivariate analyses. Two patients experienced transient dizziness or facial sensory symptoms, which resolved with medical management. CONCLUSION Pseudo-progression was observed in 40% of sporadic VS cases after GKRS and typically resolved without additional intervention. Tumor enlargement within 2 years post-treatment, particularly in older patients or those with pre-existing necrosis, can be safely monitored with clinical and radiological follow-up. Recognizing pseudo-progression is essential to avoid unnecessary treatments.