Postoperative Proton Therapy for Chordomas and Chondrosarcomas of the Spine: Adjuvant Versus Salvage Radiation Therapy

Study Design. Retrospective comparative cohort series. Objective. The aim of this study was to evaluate patients treated with proton therapy for chordoma and chondrosarcoma of the spine in the postoperative setting and to report local control, relapse-free, and overall survival outcomes. Summary of Background Data. Margin-negative resection of spinal chordomas and chondrosarcomas can be challenging, so adjuvant radiotherapy is often recommended. However, delivery of adequate radiotherapy is complicated by the relative radioresistance of these tumors, necessitating high doses, as well as the proximity of the spinal cord and exiting nerve roots increasing the risk for toxicity. Proton radiotherapy has favorable physical properties for avoiding nearby nontarget structures and is increasingly used for such lesions. Methods. Nineteen patients who underwent postoperative proton therapy at a single institution from 2006 to 2012 were identified including 13 with chordoma and 6 with chondrosarcoma. Surgical approach varied by tumor location in the cervical (n = 3), thoracic (n = 1), lumbar (n = 2), or sacral (n = 13) spine. Eight patients were categorized as receiving "early adjuvant" and 11 patients as receiving "salvage" treatment, as determined by initiation of radiation therapy after primary surgery or local recurrence, respectively. The median radiation dose delivered was 70 Gy relative biologic effectiveness (range: 56-78 Gy relative biologic effectiveness). Results. For the entire cohort, 2-year local control, relapse-free survival, and overall survival were 58%, 51.9%, and 93.3%, respectively. The early adjuvant group had significantly higher 2-year local control (80% vs. 45.5%; P = 0.024). Conclusion. Patients referred early for primary adjuvant radiation therapy after surgery had higher rates of disease control than those referred for salvage treatment of recurrent disease. Recurrence rates in our cohort were higher overall than other published series, indicating that even higher radiation doses may be helpful for further improving local control in the presence of gross or recurrent disease.