Long-term Outcomes Following Proton-based Radiation Therapy for Pediatric Chordomas and Chondrosarcomas of the Mobile Spine and the Sacrum.

PURPOSE: To report the first cohort of children with spinal and sacrococcygeal chordomas (CH) and chondrosarcomas (CHS) treated with proton-based radiation therapy (PRT).

MATERIALS AND

METHODS

Between 1989 and 2019, 52 pediatric patients ≤22 years old with spinal CH (n = 43) or CHS (n = 9) were treated with PRT at a single institution. The primary tumor originated in the C-spine (n = 37, 71%), T-spine (n = 6, 12%), L-spine (n = 7, 14%), or sacrum (n = 2, 3%). The CH group included 33 conventional and 10 atypical/poorly differentiated CH. The CHS group included 5 conventional and 4 mesenchymal CHS. Pre-RT chemotherapy was administered to 13 (25%) patients. Salvage radiation was delivered to 13 (25%) patients with progressive disease. The median total dose was 74.5 Gy (RBE) [IQR, 69.8-76 Gy (RBE)], delivered in 1.8 to 2.5 Gy (RBE) daily fractions. Primary endpoints were overall survival (OS), disease-specific survival (DSS), and progression-free survival (PFS). A univariate and multivariable Cox regression analysis was performed to identify prognostic and predictive factors.

RESULTS

At a median follow-up of 11.4 years (IQR, 5.7-19.8) from the date of diagnosis, 17 (32.7%) patients recurred (8 local, 7 distant, and 2 iatrogenic). Fifteen of these patients died of disease. The 5-, 10-, and 20-year OS were 82.7%, 72.3% and 72.3%, respectively. The 5-, 10-, and 20-year DSS were 86.1%, 77.5%, and 77.5%, respectively. The 5-, 10-, and 20-year PFS were 72.3%, 70.1% and 70.1%, respectively. The 20-year OS, DSS, and PFS for conventional CH were 93.9%, 97%, and 87.9%, respectively. Factors significantly associated with worse outcomes were poorly differentiated CH subtype, pre-RT chemo, and low KPS (P < .05). Pre-RT tumor progression was found to be a significant prognostic factor for PFS (P = .02). Two patients developed late grade 3 toxicities.

CONCLUSIONS

This is the largest study of pediatric spinal and sacrococcygeal CH/CHS to date. High-dose PRT following surgical resection offers high disease control rates for conventional CH/CHS.