Influence of incidental radiation dose in the subventricular zone on survival in patients with glioblastoma multiforme treated with surgery, radiotherapy, and temozolomide

Purpose To determine if there is an association between the incidental radiation dose to the subventricular zone and survival in patients with glioblastoma multiforme treated with surgery, radiotherapy and temozolomide. Methods and materials Sixty-five patients, treated between 2006 and 2015, were included in this retrospective study. The doses (75th percentile; p75) administered to the ipsilateral, contralateral and bilateral subventricular zone were compared to overall survival and progression-free survival using Cox proportional hazards models. Covariates included: age, sex, surgery, tumor location, and concomitant and adjuvant temozolomide. Results Median progression-free survival and overall survival were 11.5 ± 9.96 and 18.8 ± 18.5 months, respectively. The p75 doses to the ipsilateral, contralateral and bilateral subventrivular zone were, respectively, 57.30, 48.8, and 52.7 Gy. Patients who received a dose ≥48.8 Gy in the contralateral subventricular zone had better progression-free survival than those who received lower doses (HR 0.46; 95% CI 0.23–0.91 P = 0.028). This association was not found for overall survival (HR 0.60; 95% CI 0.30–1.22 P = 0.16). Administration of adjuvant temozolomide was significantly associated with improved progression-free survival (HR 0.19; 95% CI 0.09–0.41 P < 0.0001) and overall survival (HR 0.11; 95% CI 0.05–0.24 P = 0.001). In the subgroup of 46 patients whose O6 - methylguanine - DNA methyltransferase gene promoter status was known, the methylation had no effect on either progression-free survival ( P = 0.491) or overall survival ( P = 0.203). Conclusion High-dose radiation in the contralateral subventricular zone was associated with a significant improvement in progression-free survival but not overall survival in patients treated for glioblastoma multiforme.