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.
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.
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).
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.