How do you approach treatment of an unresectable sacral chordoma?

Definitive RT, preferably with protons.

Agree. Definitive RT with protons.

79.2 Gy (RBE) in 44 fractions to GTV.

50.4 Gy (RBE) in 28 fractions to CTV.

As stated, definitive-intent RT. Evidence is strongest for protons, though SBRT is also a consideration. The available data are reviewed here: Konieczkowski et al., 32147017.

Outcomes for unresected chordomas are actually quite promising when treated at experienced centers—e.g., Kabolizadeh et al., P...