Salvage Stereotactic Radiotherapy for Recurrent Glioblastoma Multiforme: Clinical Outcomes from a Multi-Institutional Registry

Abstract

**Objectives:** The purpose of this study was to evaluate the potential benefits of dose escalation for overall survival (OS) and assess related toxicities following stereotactic radiotherapy (SRT) for recurrent glioblastoma multiforme (GBM) patients. **Methods:** The RSSearch® Patient Registry was screened for patients with recurrent GBM treated with SRT between June 2007 to July 2015. The impact of potential prognostic factors on OS were evaluated using the Kaplan-Meier method and continuous log rank analysis. Prognostic factors examined included prescription dose, GTV, RPA class, initial KPS, patient age, tumor location, and single vs. multifocal recurrence. Logistic regression was utilized to evaluate the relationship between prescription dose and toxicities (graded by CTCAE guidelines). **Results:** Forty-seven patients treated with SRT (11 with 3 fractions and 36 with 5 fractions) were identified. Median OS for the cohort was 6.62 months (range: 0.33 months - 38.9 months). Of prognostic factors examined, GTV ≥ 25 cc trended towards poorer prognosis (median OS of 6.23 months vs. 8.63 months; p = 0.0597) as did initial KPS < 70% (2.63 months vs. 8.3 months; p = 0.1168). Patients treated with SRT of 5 fractions and prescription doses ≥ 30 Gy had a higher median OS (8.96 months vs. 5.65 months; p = 0.0904). However, significant survival benefits were not noted from SRT of 5 fractions and prescription doses ≥ 35 Gy (7.61 months vs. 6.47 months; p = 0.4361). Roughly 13% of patients reported side effects such as fatigue, alopecia, and mental status changes with all reported toxicities being either Grade 1 or 2. Doses ≥ 35 Gy for patients treated with SRT of 5 fractions were associated with increased side-effect incidence (p = 0.049). **Conclusion:** Salvage SRT was relatively well-tolerated and resulted in similar survival outcomes that have been previously reported in the literature. Dose escalation seems to trend towards better outcomes for SRT of 5 fractions. Prospective studies are warranted to examine the possible benefits of novel adjuvant therapies in combination with SRT given the poor prognosis of recurrent GBM.