High-dose hypofractionated stereotactic body radiotherapy for spinal chordoma

Objective: Spinal chordoma is locally aggressive and has a high rate of recurrence, even after en bloc resection. Conventionally fractionated adjuvant radiation leads to suboptimal tumor control, and data regarding hypofractionated regimens are limited. The authors hypothesized that neoadjuvant stereotactic body radiotherapy (SBRT) may overcome its intrinsic radioresistance, improve surgical margins, and allow preservation of critical structures during surgery. The purpose of this study is to review the feasibility and early outcomes of high-dose hypofractionated SBRT, with a focus on neoadjuvant SBRT.

Methods: Electronic medical records of patients with spinal chordoma treated using image-guided SBRT between 2009 and 2019 at a single institution were retrospectively reviewed.

Results: Twenty-eight patients with 30 discrete lesions (24 in the mobile spine) were included. The median follow-up duration was 20.8 months (range 2.3-126.3 months). The median SBRT dose was 40 Gy (range 15-50 Gy) in 5 fractions (range 1-5 fractions). Seventeen patients (74% of those with newly diagnosed lesions) received neoadjuvant SBRT, of whom 15 (88%) underwent planned en bloc resection, all with negative margins. Two patients (12%) developed surgical wound-related complications after neoadjuvant SBRT and surgery, and 4 (two grade 3 and two grade 2) experienced postoperative complications unrelated to the surgical site. Of the remaining patients with newly diagnosed lesions, 5 received adjuvant SBRT for positive or close surgical margins, and 1 received SBRT alone. Seven recurrent lesions were treated with SBRT alone, including 2 after failure of prior conventional radiation. The 2-year overall survival rate was 92% (95% confidence interval [CI] 71%-98%). Patients with newly diagnosed chordoma had longer median survival (not reached) than those with recurrent lesions (27.7 months, p = 0.006). The 2-year local control rate was 96% (95% CI 74%-99%). Among patients with radiotherapy-naïve lesions, no local recurrence was observed with a biologically effective dose ≥ 140 Gy, maximum dose of the planning target volume (PTV) ≥ 47 Gy, mean dose of the PTV ≥ 39 Gy, or minimum dose to 80% of the PTV ≥ 36 Gy (5-fraction equivalent doses). All acute toxicities from SBRT were grade 1-2, and no myelopathy was observed.

Conclusions: Neoadjuvant high-dose, hypofractionated SBRT for spinal chordoma is safe and does not increase surgical morbidities. Early outcomes at 2 years are promising, although long-term follow-up is pending.