Outcomes for Spine Stereotactic Body Radiation Therapy and an Analysis of Predictors of Local Recurrence
Menée à partir de données portant sur 285 patients présentant des métastases vertébrales (n=332 au total) traitées entre 2002 et 2012 (durée médiane de suivi : 33 mois), cette étude évalue l'efficacité, du point de vue du taux actuariel de contrôle local et du taux de survie globale à 1 an, l'efficacité d'une radiothérapie corporelle stéréotaxique, puis identifie les facteurs prédictifs associés à une récidive locale
Purpose : To investigate local control, survival outcomes, and predictors of local relapse for patients treated with spine stereotactic body radiation therapy (SBRT). Methods : We reviewed the records of 332 spinal metastases consecutively treated with SBRT between 2002 and 2012. The median follow-up for all living patients was 33 months (range, 0-111). Endpoints were overall survival (OS) and local control (LC); recurrences were classified as either in-field or marginal. Results : The 1-year actuarial LC and OS rates were 88% and 64%. Patients with local relapses had poorer dosimetric coverage of the GTV compared to patients without recurrence (Dmin BED 23.9 vs. 35.1 Gy, P<0.001; D98 BED 41.8 vs. 48.1 Gy, P=0.001; D95 BED 47.2 vs. 50.5 Gy, P=0.004). Furthermore, patients with marginal recurrences had poorer prescription coverage of the GTV (86% vs. 93%, P=0.01) compared to those with in-field recurrences, potentially because of more upfront spinal canal disease (78% vs. 24%, P=0.001). Using a Cox regression univariate analysis, patients with a GTV BED Dmin ≥ 33.4 Gy (median dose) (equivalent to 14 Gy in 1 fraction) had a significantly higher 1-year LC rate (94% vs. 80%, P=0.001) compared to patients with a lower GTV BED Dmin; this factor was the only significant variable on multivariate Cox analysis associated with LC (P=0.001, HR 0.29, 95% CI 0.14-0.60), and also was the only variable significant in a separate competing risk multivariate model (P=0.001, HR 0.30, 95% CI 0.15-0.62). Conclusions : SBRT offers durable control for spinal metastases, but there is a subset of patients that recur locally. Patients with local relapse had significantly poorer tumor coverage, which was likely attributable to treatment planning directives that prioritized the spinal cord constraints over tumor coverage. When possible, we recommend maintaining a GTV Dmin above 14 Gy in 1 fraction and 21 Gy in 3 fractions.
http://www.redjournal.org/article/S0360-3016(15)00370-3/abstract