KEY POINTS
- The retrospective Heidelberg analysis included 157 patients with nonmetastatic sacrococcygeal chordoma treated from 2011–2025: 66 received 64 Gy(RBE) in 16 × 4 Gy(RBE) and 91 received 66 Gy(RBE) in 22 × 3 Gy(RBE).
- Treatment was definitive after biopsy alone in 55% and postoperative in 45%; 17% were treated for recurrent disease. Median clinical target volume was 832 cm³.
- Two- and four-year local progression-free survival was 83.4% and 71.8% with 16 × 4 Gy(RBE), versus 71.8% and 52.3% with 22 × 3 Gy(RBE). The difference did not reach statistical significance (p = 0.140).
- Overall survival was 96.5% and 85.4% at two and four years with 16 fractions versus 98.6% and 91.2% with 22 fractions (p = 0.816).
- Female sex (HR 2.44, 95% CI 1.46–4.08) and treatment for recurrent disease (HR 3.01, 95% CI 1.49–6.06) independently predicted local progression.
- Sacral insufficiency fractures occurred significantly more often after 16 × 4 Gy(RBE): 47% versus 24% (p = 0.003). The corresponding calculated EQD2 values were 96.0 versus 82.5 Gy.
- Fractionation was largely determined by treatment era rather than randomization, and follow-up differed between cohorts, limiting causal interpretation of both efficacy and late toxicity differences.
CLINICAL TAKEAWAY
The numerically stronger local control with 16 × 4 Gy(RBE) did not translate into a statistically significant survival advantage and came with almost twice the fracture rate. These data support the more conservative 66 Gy(RBE) in 22 fractions approach currently used at Heidelberg while prospective fractionation data remain unavailable.
SOURCE
International Journal of Radiation Oncology, Biology, Physics