Robust IMPT and follow-up toxicity in skull base chordoma and chondrosarcoma-asingle-institution clinical experience.

Abstract

Chordomas and chondrosarcomas of the skull base are rare, slowly growing malignant bone neoplasms. Despite their radioresistant properties, proton therapy has been successfully used as an adjunct to resection or as adefinitive treatment. Herewith, we present our experience with robustly optimized intensity-modulated proton therapy (IMPT) and related toxicities in skull base chordoma and chondrosarcoma patients treated at HollandPTC, Delft, the Netherlands. Clinical data, treatment plans, and acute toxicities of patients treated between July 2019 and August 2021 were reviewed. CT and 3.0T MRI scans for treatment planning were performed in supine position in athermoplastic mold. In total, 21dose optimization and 28dose evaluation scenarios were simulated. Acute toxicity was scored weekly before and during the treatment according to the CTCAE v4.0. Median follow-up was 35months (range 12-36months). Overall, 9chordoma and 3chondrosarcoma patients with 1-3 resections prior to IMPT were included; 4patients had titanium implants. Brainstem core and surface and spinal cord core and surface were used for nominal plan robust optimization in 11, 10, 8, and 7patients, respectively. Middle ear inflammation, dry mouth, radiation dermatitis, taste disorder, and/or alopecia of grades 1-3 were noted at the end of treatment among 6patients without similar complaints at inclusion; symptoms disappeared 3months following the treatment. Robustly optimized IMPT is clinically feasible as apostoperative treatment for skull base chordoma and chondrosarcoma patients. We observed acceptable early toxicities (grade1-3) that disappeared within the first 3months after irradiation.