(P 148) CHARACTERISTICS AND OUTCOMES OF CHONDROSARCOMA PATIENTS TREATED WITH PROTON THERAPY: A SYSTEMATIC REVIEW OF PUBLISHED SERIES

Objective: Chondrosarcoma is a rare malignant cartilage tumor that typically arises in the appendicular skeleton and pelvis, but can also involve the spine and skull base. It is notably resistant to chemotherapy and conventional photon-based radiotherapy (RT). While surgery remains the mainstay of treatment, RT plays a key role when complete resection is not feasible or when margins are close or positive. Proton therapy (PT), with its superior dose conformity, allows for high-dose delivery while sparing adjacent critical structures and is increasingly used in this setting. The objective of this study is to systematically evaluate patient characteristics and clinical outcomes associated with proton therapy for chondrosarcoma, with the goal of informing optimal treatment strategies and guiding future research directions.

Methods: We conducted a review of published series reporting outcomes in chondrosarcoma patients treated with PT. Data on patient demographics, tumor site, histologic grade, radiation dose, toxicity profiles, and clinical outcomes were extracted and analyzed.

Results: Most cohorts included adults with skull base tumors, predominantly grade 1 or 2, treated postoperatively with PT at median doses of 66-74 Gy (RBE or CGE). For skull base chondrosarcoma, reported 3-year local control (LC) rates ranged from 86% to 100%, and 5-year LC rates varied from 75% to 94%. Five-year overall survival (OS) rates, where reported, ranged from 84% to 100%. Outcomes for spinal and sacral tumors are more variable and generally lower. Severe late toxicities are uncommon, with sensorineural hearing loss and temporal lobe necrosis being the most notable adverse events.

Conclusion: PT provides excellent LC and OS outcomes for chondrosarcoma, particularly in skull base tumors treated postoperatively. Its favorable toxicity profile supports its continued use as standard of care in anatomically challenging cases. Further studies are needed in non-skull base and pediatric populations.