Impact of subventricular zone irradiation on outcome of patients with glioblastoma

Glioblastoma (GBM) is characterized by early relapse and mortality. Treatment resistance could be a characteristic exhibited by pro-genitor neoplastic cells that reside in the subventricular zone (SVZ). This retrospective study was conducted to assess the correlation of SVZ doses and survival in patients with GBM.Forty-seven patients with GBM treated with radiotherapy, concurrent and adjuvant temozolomide therapy, and whose dosimetry data were available were included. The ipsilateral and contralateral SVZs were delineated on co-registered magnetic resonance imaging-computed tomography images as a 5-mm margin along the lateral wall of the lateral ventricles. Median radiotherapy dose prescribed was 59.4 Gy. The mean ipsilateral, contralateral, and bilateral SVZ doses were 56.3 Gy (range 33-63 Gy), 50.4 Gy (range 23-79 Gy), and 52 Gy (28-69 Gy). The progression-free survival (PFS) and overall survival (OS) were calculated from the date of surgery to the date of radiologic and/or clinical progression and death/last follow-up, respectively. Survival probability was estimated using the Kaplan-Meier method. Log-rank test was used to test the significance between groups. Cox proportional hazards analyses were used to identify prognostic factors.At a median follow-up of 19 months, all patients had relapsed. Most recurrences were infield (n = 39). The median PFS and OS were 17 and 19 months, respectively. The PFS and OS at 2 years were 36.2% and 21.3%, respectively. Patients who received ipsilateral SVZ dose of ≥56 Gy appeared to have better but nonsignificant median PFS and OS. Patients receiving contralateral SVZ doses ≥50 Gy showed a similar trend. Only the number of adjuvant temozolomide (≥6 cycles) showed prognostic impact.This retrospective study indicated a trend toward improved-albeit nonsignificant-survival with higher dose to the ipsilateral and contralateral SVZs. A well-designed prospective randomized study is required to identify patients who would benefit from intentional SVZ targeting.