Although spine stereotactic body radiotherapy (SBRT) is considered a standard of care in the mobile spine, mature evidence reporting outcomes specific to sacral metastases is lacking. Furthermore, there is a need to validate the existing sacral SBRT international consensus contouring guidelines to define the optimal contouring approach. We report mature rates of local failure (LF), adverse events, and the impact of contouring deviations in the largest experience to date specific to sacrum SBRT. Consecutive patients who underwent sacral SBRT from 2010-2021 were retrospectively reviewed. Primary endpoint was magnetic resonance imaging-based LF with a specific focus on adherence to target volume contouring recommendations. Secondary endpoints included vertebral compression fracture (VCF) and neural toxicity. Of the 215 sacrum segments treated in 112 patients, most received 30 Gy/4 fractions (51%), 24 Gy/2 fractions (31%), or 30 Gy/5 fractions (10%). Sixteen percent of segments were non-adherent to the consensus guideline with a more restricted target volume (under-contoured). The median follow-up was 21.4 months (range, 1.5-116.9). The cumulative incidence of LF at 1 and 2 years was 18.4% and 23.1%, respectively. In those with guideline adherent vs. non-adherent contours, the LF rate at 1 year was 15.1% vs. 31.4% and at 2 years 18.8% vs. 40.0% (HR=2.5, 95% CI 1.4-4.6, p=0.003), respectively. On multivariable analysis, guideline non-adherence (HR=2.4, 95% CI 1.3-4.7, p=0.008), radioresistant histology (HR=2.4, 95% CI 1.4-4.1, p<0.001), and extraosseous extension (HR=2.5, 95% CI 1.3-4.7, p=0.005) predicted for an increased risk of LF. The cumulative incidence of VCF was 7.1% at 1 year and 12.3% at 2 years. Seven patients (6.3%) developed peripheral nerve toxicity, of which 4/7 had been previously radiated. Sacral SBRT is associated with high efficacy rates and an acceptable toxicity profile. Adhering to consensus guidelines for target volume delineation is recommended to reduce the risk of LF.

中文翻译：

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骶骨转移瘤的立体定向放射治疗 (SBRT)：偏离建议的目标体积描绘会增加局部失败的风险

尽管脊柱立体定向放射治疗 (SBRT) 被认为是移动脊柱的护理标准，但缺乏针对骶骨转移的成熟证据报告结果。此外，需要验证现有的骶骨 SBRT 国际共识轮廓指南，以确定最佳轮廓方法。我们报告了迄今为止最大的骶骨 SBRT 经验中局部失败 (LF) 的成熟率、不良事件以及轮廓偏差的影响。对 2010 年至 2021 年连续接受骶骨 SBRT 的患者进行回顾性分析。主要终点是基于磁共振成像的 LF，特别关注遵守目标体积轮廓建议。次要终点包括椎体压缩性骨折（VCF）和神经毒性。在 112 名患者接受治疗的 215 个骶骨节段中，大多数接受了 30 Gy/4 分次 (51%)、24 Gy/2 分次 (31%) 或 30 Gy/5 分次 (10%)。16% 的分段不遵守共识指南，目标体积更受限制（轮廓不足）。中位随访时间为 21.4 个月（范围：1.5-116.9）。1 年和 2 年 LF 的累积发生率分别为 18.4% 和 23.1%。在遵循指南与不遵循轮廓的患者中，1 年时的 LF 率为 15.1% vs. 31.4%，2 年时的 LF 率为 18.8% vs. 40.0%（HR=2.5，95% CI 1.4-4.6，p=0.003） ）， 分别。在多变量分析中，指南不依从性（HR=2.4，95% CI 1.3-4.7，p=0.008）、放射抗性组织学（HR=2.4，95% CI 1.4-4.1，p<0.001）和骨外延伸（HR= 2.5，95% CI 1.3-4.7，p=0.005）预测 LF 风险增加。VCF 1 年累积发生率为 7.1%，2 年累积发生率为 12.3%。7 名患者（6.3%）出现周围神经毒性，其中 4/7 之前曾接受过放射治疗。骶骨 SBRT 具有高有效率和可接受的毒性特征。建议遵守目标体积描绘的共识指南，以降低 LF 的风险。