High Dose Radiosurgery Targeting the Primary Tumor Sites Contributes to Survival in Patients With Skull Base Chordoma

Purpose: Skull base chordoma (SBC) is a rare, aggressive bone tumor and a challenging therapeutic target. The efficacy of stereotactic radiosurgery (SRS) for SBC remains unclear. We aimed to elucidate therapeutic factors for favorable outcomes and establish a novel therapeutic approach for SBC. Methods and Materials: This single-center retrospective study examined 47 SBCs treated with SRS. Treatment factors affecting local control rates (LCRs), remote control rates (RCRs), and overall survival (OS) were evaluated. Initially, we applied “localized-field SRS,” wherein the irradiated volume accurately included recurrent/residual tumors on the radiographic images. Since 2015, we systematically applied “extended-field SRS,” wherein the irradiated volume included the tumor location on the radiographic images and the preoperative tumor location with 2-mm margins. Results: Tumor progression was observed in 23 SBCs (49%) after SRS. Higher marginal doses ≥20 Gy resulted in a higher LCR than lower-dose treatments (92% at 2 years and 73% at 5 years vs 43% at 2 years and 21% at 3 years, P = .001). Twenty-four patients underwent extended-field SRS, and 23 underwent localized-field SRS. While the LCRs were not significantly different, extended-field SRS improved RCRs (extended-field SRS: 100% vs localized-field SRS: 46% at 5 years; P = .001) without radiation-induced adverse events. Multivariate analysis demonstrated that extended-field SRS was associated with better RCRs (P = .001) and OS (P = .001). Conclusions: Extended-field SRS achieved LCRs comparable to previous studies and excellent OS without increasing the risk of radiation-induced adverse events.