2026 Proffered Presentations
S205: ANATOMIC AND RADIOGRAPHIC PATTERNS OF RADIATION FAILURE IN RECURRENT CLIVAL CHORDOMAS
Danielle D Dang, MD, MA; Sukwoo Hong, MD; Paul D Brown, MD; Bruce Pollock, MD; Michael Link, MD; Maria Peris Celda, MD, PhD; Anita Mahajan, MD; Jamie J Van Gompel, MD; Nadia N Laack, MD; Eric J Lehrer, MD; Mayo Clinic Rochester
Introduction: Clival chordomas are radioresistant tumors that recur locally in 40-50% of patients. This is despite maximal surgical resection and dose-escalated conventionally fractionated adjuvant radiation treatment (RT). However, anatomic and dosimetric patterns of failure have not been well characterized.
Objectives: To characterize failure patterns following surgical resection and adjuvant radiation treatment.
Methods: A retrospective review of all patients with a pathologically confirmed diagnosis of chordoma who underwent adjuvant proton RT using pencil beam scanning at Mayo Clinic between 2015 and 2022 was conducted, regardless of where the index surgery was performed. Treatment plans were generated in Eclipse (Varian Medical Systems, Palo Alto, USA). The first post-treatment surveillance MRI that demonstrated failure was co-registered to the treatment plan. Dose volume histogram data was then used to characterize failure patterns. Time to failure was calculated from the completion date of RT. Patients who underwent adjuvant RT over 6-7 weeks were included. Type I, II, and III local failures were defined as the lowest isodose line encompassing the area of recurrence, where: within 95% of the high dose, within 95% of the elective dose, and outside of these isodose lines.
Results: Please refer to Figure 1 for demographic, dosimetric, and anatomic details on the eight patients who developed treatment failure. The median follow-up was 68 months from completion of RT (range: 28-123 months). One patient (12.5%) developed a multifocal in-field recurrence (Type I and II), three (37.5%) Type II, and 50% Type III failures occurred within the follow-up period (Figures 2,3). 5 patients (62.5%) experienced multiple recurrences after initial resection and PBRT and subsequently trialed either stereotactic radiotherapy and/or chemotherapy.
Conclusion: Approximately 50% of chordoma recurrences following resection and dose-escalated proton RT occur within the elective dose volume. Given the sensitivity of chordoma to fraction size and its low α/β ratio, incorporation of hypofractionated regimens and/or stereotactic radiosurgery into adjuvant treatment paradigms may further improve outcomes in these patients.
