Lateral ventricule invasion and radiation dose to subventricular zone: Their impact to the treatment outcomes of glioblastoma

Background: This study was conducted to evaluate the recurrence patterns of GBM in regard to its contact with LVs, the relation between radiation doses to subventrivular zone (SVZ). Materials and Methods: Between 2012 and 2014, 80 adult patients with GBM were included this trial. Median follow-up period was 15 months. Median tumor size was 4.5 cm (1.3-8 cm), where 58% of the patients had a tumor larger than 4 cm. All of the lesions were located supratentorial part of brain. Tumors were classified based on whether the mass involved the SVZ and/or LVs. Reccurrence patterns and treatment outcomes were compared. Results: Tumor progression occurred in 60 (75%) of the patients. Of those 31 (51.6%) were    in-field. Median progression-free survival (PFS) and median overall survival (OS) times were 11 and 15 months, respectively. On multivariate analysis, the negative prognostic factors were maximal surgical resection (p=0.027), LV-invading tumor (p=0.001) and p53 positivity (p=0.034) for PFS. It was found that the patients receiving >50 Gy to iSVZ dose (p=0.024) or >40 Gy to cSVZ dose (p=0.002) or >40 Gy to bSVZ dose (p=0.028) or >50 Gy to bSVZ dose (p=0.008) tended to have more recurrences. Both in-field and out-field recurrences were not affected by higher radiation doses. Conclusion: LVs invading and/or location close to the SVZs can be considered as an important prognostic factor in terms of decreased PFS and OS rates. Additionally both SVZs sparing and dose escalation to SVZs approaches are required to be evaluated in further researches.