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Despite the radical treatments applied, local recurrence is encountered in the majority of high-grade gliomas (HGG). There is no standard treatment when recurrence is detected, but stereotactic radiotherapy (SRT) is a preferable alternative in this context. The aim of this retrospective study is to evaluate the efficacy of SRT for recurrent HGG, and to investigate the factors that affect survival outcomes.

From September 2013 to March 2021, a total of 59 patients with 64 lesions were re-irradiated with CyberKnife stereotactic radiotherapy. The primary endpoints of the study were overal survival (OS), progression free survival (PFS) and local control rates (LCR). Survival curves were estimated with the Kaplan-Meier method and compared using log-rank test, hazard ratios were estimated using Cox regression analysis.

Eleven of the patients were WHO grade 3 anaplastic astrocytomas, and 48 of the patients were WHO grade 4 glioblastomas. All of the patients received a median of 60 Gy (59.4-60 Gy) of postoperative radiotherapy (RT), and 51 of them received oral temozolomide chemotherapy, concurrently. The median time to first recurrence was 13 (4-85) months. 12 of the patients had a second surgery before re-irradiation. SRT was performed as a median prescription dose of 30 Gy (range 15-30), with a median of 5 fractions (1–5). The median follow-up time was 4 months (range 1–57), 11 patients were alive at the last follow-up. The median OS after re-irradiation was 8 (95% CI: 4.66-11.33) months, and 1- and 2-y OS were 33.2% and 14.2%, respectively. In the univariate analysis, age <65 years (p =0.003), grade 3 gliomas (p =0.023), size of tumor <2cm (p=0.018) were associated with better survival. Grade 3 gliomas (p =0.027), size of tumor <2cm (p=0.008) were remained independent prognostic factors for OS in the multivariate analysis. Recurrence after re-irradiation was detected in 20 patients, 6 of them belonged to new lesions. The median PFS after re-irradiation was 5 (95% CI: 3.39-6.60) months, and 1- and 2-y PFS were 24.5% and 9.5%, respectively. In the univariate analysis, age <65 years (p =0.033), grade 3 gliomas (p =0.037), stable response at first evaluation with magnetic resonance imaging (p=0.003), and time to recurrence >9 months (p=0.021) were associated with improved PFS. Stable response (p =0.001) was remained prognostic factor for PFS in the multivariate analysis. LCR were 62.7% and 33.9% at the first and last follow up. There was no serious toxicity.

SRT is a viable treatment modality with significant survival contribution in recurrent HGG. It should be considered when deciding on re-irradiation during follow-up, as it may have a favorable prognostic effect on survival in patients with tumor size <2 cm.