Impact of subventricular zone irradiation on outcome of patients with glioblastoma.

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.