Stereotactic radiotherapy with CyberKnife-M6 for patients with clivus chordoma

Abstract Objectives Chordomas are rare tumors and have high rates of local recurrences despite aggressive surgery and conventional radiotherapy (RT). Technological advances allow delivery of higher RT doses more safely. The aim was to evaluate the efficacy and dosimetric factors of stereotactic radiotherapy (SRT) with the next-generation CyberKnife-M6 (CK-M6) in patients with clivus chordoma. Methods Between 2020 and 2023, 11 patients were treated at the Bursa Uludag University. All but one patient had classical chordoma histology. A median dose of 32.5 Gy (25–35) in five fractions was administered. Patients were followed with serial magnetic resonance imaging after treatment. Results Median follow-up was 31 months (14–52). The median age was 58 (49–69). The most common symptoms were visual disturbances (72 %) and headache (18 %). The median planning target volume was 20.85 cc (4.27–33.54), and the median beam-on time was 18 min (14–21). The median BED 2.45 value was 118.72 Gy (76.02–135). Risky organ doses were not exceeded in any patients. Asymptomatic radionecrosis was observed in three cases (27 %) by imaging at a median of 24 months (12–36). At the last control, all patients were alive, and local control was achieved in 10 patients (91 %). Two-year progression-free survival (PFS) was 100 %, decreased to 75 % at 3 years. Conclusions Our results suggest that CK-M6-based SRT appears to be an effective and safe treatment option for patients with clivus chordoma, with high local control and a low incidence of late toxicity. A longer follow-up is needed to evaluate the long-term results.