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• Intraoperative radiotherapy as a boost added to the standard of care treatment is safe and feasible. • Apparently, intraoperative radiotherapy for glioblastoma increases the overall survival rate (~25% at 3 years). • Local failure was first progression in 35.3% of cases. • No additional severe toxicity was related to this modality in comparison to conventional treatment. To report the results of the first international pooled analysis of patients with glioblastoma treated with intraoperative radiotherapy (IORT) in addition to standard of care therapy. Data from 51 patients treated at five centers in Germany, China and Peru were analyzed. All patients underwent tumor resection followed by a single application of IORT (10–40 Gy, prescribed to the applicator surface) with low-energy X-rays. Thereafter, standard adjuvant radiochemotherapy and maintenance chemotherapy were applied. Factors of interest were overall survival (OS), progression-free survival (PFS), local PFS (L-PFS; defined as appearance of new lesions ≤1 cm to the cavity border) and distant PFS (D-PFS; lesions >1 cm). The same endpoints were estimated at 1-, 2- and 3-years using the Kaplan-Meier method. Additionally, rates and severity (as per Common Terminology Criteria for Adverse Events Version 5.0) of radionecrosis (RN) were analyzed. The median age was 55 years (range: 16–75) and the median Karnofsky Performance Status was 80 (20–100). At a median follow-up of 18.0 months (2–42.4), the median OS, PFS, L-PFS and D-PFS were 18.0 months (95% CI: 14.7–21.3), 11.4 months (95%CI: 7.58–15.22), 16 months (95%CI: 10.21–21.8) and 30.0 months (95%CI: 18.59 – 41.41), respectively. The estimated 1-, 2- and 3-year OS, PFS, L-PFS and D-PFS were 79.5%, 38.7% and 25.6%; 46.2%, 29.4%, and 5.9%; 60.9, 37.9%, and 12.6%; and 76.7%, 65.0%, and 39.0% respectively. First progression occurred locally in only 35.3% of cases. Grade 1 RN was detected in 7.8% and grade 3 in 17.6% of the patients. No grade 4 toxicity was reported and no treatment-related deaths occurred. Compared to historical data, this pooled analysis suggests improved efficacy and safety of IORT with low-energy X-rays for newly diagnosed glioblastoma. Prospective data is warranted to confirm these findings. [ABSTRACT FROM AUTHOR]