The risk of local failure is three and a half times greater after conventional external beam radiotherapy (cEBRT) when compared to stereotactic body radiotherapy (SBRT) for spinal metastases, a recent study which won Best Paper at Global Spine Congress 2022 (1–4 June; Las Vegas, USA), has found.
The results of the study—a retrospective analysis from an institutional cohort of patients enrolled on a phase II/III randomised controlled trial with mature follow-up—were presented by K. Liang Zeng (Sunnybrook Health Sciences Centre, Toronto, Canada), and further showed that cEBRT is also associated with greater retreatment rates and that SBRT may be “particularly indicated for ‘mass’ type and radioresistant spinal metastases”.
The study authors note that durability of tumour control “is increasingly recognised as an important endpoint given that patients with metastatic disease are surviving longer”.
A total of 229 patients were previously randomised on NCIC CCTG SC.24 to either 24 Gy in two SBRT fractions or 20 Gy in five cEBRT fractions. Of the 229 patients, 137 (60%) were enrolled from the Sunnybrook Health Sciences Centre of which 66 patients with 119 spine segments were treated with SBRT, and 71 patients with 169 segments treated with cEBRT. This study represents a retrospective review of this cohort. The primary outcome measures consisted of MR-based local control, overall survival (OS) and retreatment rates, as patients were followed off-protocol after trial completion with a full spine MRI and clinical assessment every three months.
The median follow-up was 11.3 months (interquartile range: 5.3–28.5 months) and median OS was 21.6 and 18.9 months in the SBRT and cEBRT cohorts, respectively.
The SBRT and cEBRT cohorts were balanced with respect to radioresistant vs. radiosensitive histology and presence of ‘mass’ (paraspinal and/or epidural disease extension). Risk of local failure at six, 12 and 24 months were 2.8% vs.11.2%, 6.1% vs. 28.4% and 14.8% vs. 35.6%, favouring SBRT vs. cEBRT, respectively.
cEBRT (hazard ratio [HR]: 3.48, 95% confidence interval [CI]: 1.94–6.25, p<.001) and presence of ‘mass’ (HR: 2.07, 95% CI: 1.29–3.31, p=0.002) were independent significant predictors of local failure on multivariate analysis.
The one-year retreatment rates were 3.4% and 20.3% after SBRT vs. cEBRT, respectively (p=0.004), and the median time to retreatment was 22.9 months vs. 9.5 months in the SBRT vs. cEBRT cohorts, respectively. Radioresistant histology (HR: 2.94, 95% CI: 1.62–5.35, p<0.001), cEBRT (HR: 2.36, 95% CI: 1.13–4.95, p=0.023) and ‘mass’ (HR: 1.83, 95% CI: 1.01–3.34, p=0.048) independently predicted retreatment. A greater proportion of iatrogenic vertebral compression fractures (VCFs) occurred after SBRT and Grade 3 VCF were isolated to this cohort.
This important publication, which in addition to the primary endpoint of NCIC CCTG SC.24 that demonstrated superiority of 24 Gy in two SBRT fractions over cEBRT for complete pain response, indicates additional benefits supporting spine SBRT of reducing the risk of local failure and the need for irradiation, note the researchers.