RONC-32. LOCAL CONTROL FOLLOWING PROTON THERAPY FOR PEDIATRIC CHORDOMA

BACKGROUND: Due to the location and high dose required for disease control, pediatric chordomas are theoretically well-suited for treatment with proton therapy, but their low incidence limits the clinical outcome data available in the literature. METHODS AND MATERIALS: Between 2008 and 2019, 29 patients with a median age of 14.8 years (range, 3.8–21.8) received proton therapy for non-metastatic chordoma at a single institution. Twenty-four tumors arose in the clivus/cervical spine region and 5 in the lumbosacral spine. Twenty-six tumors demonstrated well-differentiated histology and 3 were dedifferentiated or not otherwise specified (NOS). Approximately half of the tumors underwent specialized testing: 14 were brachyury-positive and 10 retained INI-1. Seventeen patients had gross disease at the time of radiation. The median radiation dose was 73.8 GyRBE. RESULTS: With a median follow-up of 4.3 years (range, 1.0–10.7), the 5-year estimates of local control, progression-free survival, and overall survival rates were 85%, 82%, and 86%, respectively. Excluding 3 patients with dedifferentiated/NOS chordoma, the 5-year local control, progression-free survival, and overall survival rates were 92%, 92%, and 91%, respectively. Serious toxicities included 3 patients with hardware failure or related infection requiring revision surgery, 2 patients with hormone deficiency, and 2 patients with Eustachian tube dysfunction causing chronic otitis media. CONCLUSION: In pediatric patients with chordoma, proton therapy is associated with a low risk of serious toxicity and high efficacy, particularly in well-differentiated tumors. Complete resection may be unnecessary for local control and destabilizing operations requiring instrumentation may result in additional complications following therapy.