Study Protocol: Early Stereotactic Gamma Knife Radiosurgery to Residual Tumor After Surgery of Newly Diagnosed Glioblastoma (Gamma-GBM).

Background: Glioblastoma (GBM) is the most common malignant brain tumor in adult patients. Tumor recurrence commonly occurs around the resection cavity, especially after subtotal resection (STR). Consequently, the extent of resection correlates with overall survival (OS), suggesting that depletion of postoperative tumor remnants will improve outcome.

Objective: To assess safety and efficacy of adding stereotactic radiosurgery (SRS) to the standard treatment of GBM in patients with postoperative residual tumor.

Methods: Gamma-GBM is a single center, open-label, prospective, single arm, phase II study that includes patients with newly diagnosed GBM (intraoperative via frozen sections) who underwent STR (residual tumor will be identified by native and contrast enhanced T1-weighted magnetic resonance imaging scans). All patients will receive SRS with 15 Gy (prescribed to the 50% isodose enclosing all areas of residual tumor) early (within 24-72 h) after surgery. Thereafter, all patients undergo standard-of-care therapy for GBM (radiochemotherapy with 60 Gy external beam radiotherapy [EBRT] plus concomitant temozolomide and 6 cycles of adjuvant temozolomide chemotherapy). The primary outcome is median progression-free survival, secondary outcomes are median OS, occurrence of radiation induced acute (<3 wk), early delayed (<3 mo), and late (>3 mo post-SRS) neurotoxicity and incidence of symptomatic radionecrosis.

Expected Outcomes: We expect to detect efficacy and safety signals by the immediate application of SRS to standard-of-care therapy in newly diagnosed GBM.

Discussion: Early postoperative SRS to areas of residual tumor could bridge the therapeutic gap between surgery and adjuvant therapies.