Location of subventricular zone recurrence and its radiation dose predicts survival in patients with glioblastoma

Glioblastomas are aggressive brain tumors that frequently recur in the subventricular zone (SVZ) despite maximal treatment. The purpose of this study was to evaluate imaging patterns of subventricular progression and impact of recurrent subventricular tumor involvement and radiation dose to patient outcome. Retrospective review of 50 patients diagnosed with glioblastoma and treated with surgery, radiation, and concurrent temozolomide from January 2012 to June 2013 was performed. Tumors were classified based on location, size, and cortical and subventricular zone involvement. Survival was compared based on recurrence type, distance from the initial enhancing tumor (local ≤ 2 cm, distant > 2 cm), and the radiation dose at the recurrence site. Progression of enhancing subventricular tumor was common at both local (58%) and distant (42%) sites. Median survival was better after local SVZ recurrence than distant SVZ recurrence (8.7 vs. 4.3 months, p = 0.04). Radiation doses at local SVZ recurrence sites recurrence averaged 57.0 ± 4.0 Gy compared to 44.7 ± 6.7 Gy at distant SVZ recurrence sites (p = 0.008). Distant subventricular progression at a site receiving ≤ 45 Gy predicted worse subsequent survival (p = 0.05). Glioblastomas frequently recurred in the subventricular zone, and patient survival was worse when enhancing tumor occurred at sites that received lower radiation doses. This recurrent disease may represent disease undertreated at the time of diagnosis, and further study is needed to determine if improved treatment strategies, such as including the subventricular zone in radiation fields, could improve clinical outcomes.