Subventricular zone involvement at recurrence is a strong predictive factor of outcome following high grade glioma reirradiation.

We aimed to assess the efficacy of stereotactic irradiation for patients with recurrent high-grade glioma (HGG) and identify predictive factors of progression-free survival (PFS) and overall survival (OS) following reirradiation. We identified 32 patients with recurrent brain HGG who had been treated with either single-dose (stereotactic radiosurgery) or fractionated stereotactic radiotherapy between April 2008 and October 2015. Median follow up was 21.4 months (range 12.9-23.2) and median PFS was and 3.3 months (95% CI [2.3-4.7]), respectively. OS was 90.40% (95% CI [73.09-96.80]) at 6 months and 79.55% (95% CI [59.9-90.29]) at 12 months. Univariate analysis showed that biological effective dose at isocenter ≤ 76 Gy was a poor prognostic factor for both OS (83.33 vs. 100% at 6 months, p = 0.032) and median PFS (2.7 vs. 4.7 months, p = 0.025), as was gross tumor volume (GTV) above 1 cm3 for OS (86.15 vs. 94.12% at 6 months, p = 0.043). Contact with the subventricular zone (SVZ) was also a poor prognostic factor for median PFS (2.3 vs. 4.7 months, p = 0.002). Multivariate analysis showed that SVZ contact remained a poor prognostic factor for PFS (hazard ratio = 3.44, 95% CI [1.21-9.82], p = 0.021). Results suggest that reirradiation is a safe and effective treatment option for recurrent HGG in patients with a good Karnosfsky Performance Scale score, a long progression-free interval since first radiation and limited GTV, and that contact to SVZ is a strong prognostic factor for PFS.