Proton versus photon adjuvant radiotherapy in the management of chordomas, a nationwide NCDB analysis

Introduction: Chordomas are rare tumors that originate from undifferentiated remnants of the notochord. Currently, there are no established recommendations regarding the choice of radiation modality for patients diagnosed with chordomas. Some studies have previously suggested some benefits associated with the use of proton therapy. Nonetheless, a recent Cochrane review was unable to find evidence suggesting superiority of either proton or photon therapy in the management of these tumors, encouraging the publication of large, and multi-institutional data to investigate this topic. Using a nationwide, multicentric database, we hence aimed to compare long-term survival outcomes associated with the use of proton or photon adjuvant therapy for the management of chordomas of both skull base and spine.

Methods: The NCDB was queried for chordoma cases from 2004 to 2017. Patient, tumor, and treatment characteristics were extracted from the database. The primary outcome was overall survival. Kaplan-Meier survival analyses were conducted to investigate differences in outcome on propensity score matched cohorts of patients receiving either proton or photon adjuvant radiotherapy.

Results: The first Kaplan-Meier curve, encompassing all chordoma cases, revealed no statistically significant difference in overall survival between patients treated with photon therapy and those receiving proton therapy (p = 0.39). In the second Kaplan-Meier analysis, which focused specifically on patients with skull base chordomas, no significant difference in overall survival was observed between photon therapy and proton therapy groups (p = 0.71). Focusing on patients with spine chordomas only, significant differences were found between both adjuvant treatment modalities, as proton therapy exhibited a superior overall survival advantage compared to photon therapy (p = 0.012).

Conclusion : Adjuvant radiotherapy with proton beams exhibited superiority over adjuvant radiotherapy with photon beams in the management of chordomas of the spine and sacrum but not skull base.