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Background: Sacral chordomas are rare malignant bone tumors and are often very large for complete resection. Particle therapy for these tumors, which are adjacent to the gastrointestinal tract, is restricted because the tolerance dose of the intestine is low. This study aimed to demonstrate the technical aspects and treatment results of space-making particle therapy with surgical spacer placement for sacral chordoma. We aimed to investigate the dosimetric change in the particle therapy before and after spacer placement and the safety, efficacy, and long-term outcomes of space-making particle therapy.Study Design: Twenty-one patients with sacral chordomas who were excluded from typical particle therapy were enrolled between 2007 and 2015. Gore-Tex sheets (WL Gore & Assoc) were folded and placed between the sacral and rectum. Particle therapy with 70.4 Gy (relative biologic effectiveness) was then performed.Results: The mean volume that allows 95% of the treatment plan dose of the gross tumor volume and clinical tumor volume after spacer placement was improved to 97.7% and 96.4% from preoperative values of 91.0% and 89.5%, respectively. The recurrence rate within the gross tumor volume was only 4.8%. The 4-year local progression-free survival rate was 68.4%. The 5-year overall survival rate was 100% and the adverse events were acceptable.Conclusions: Considering improvements in the dose-volume histogram after spacer placement, low recurrence rates within the gross tumor volume, good survival rates, and low incidences of side effects, treatment of sacral chordoma with space-making particle therapy shows promise. [ABSTRACT FROM AUTHOR]