Page 109 - Predicting survival in patients with spinal bone metastasesL
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                                dose and the individual SINS components, pain, bone lesion, alignment, collapse and posterolateral involvement did not show a significant association with the occurrence of an adverse event in the multivariate analysis. Even though the component location reached a significant level of association, a hazard ratio of less than one is indicative of a protective effect for developing spinal instability, rather than a harmful effect, as implied by the SINS. As a result, this variable might not provide any clinically relevant information when assessing spinal instability.
Similar to our study, Lam et al.21 retrospectively examined the relationship of the SINS and dose fractionation with the development of a spinal adverse event (SAE) in 299 patients with SBM who received radiotherapy. They found that a SINS score ≥ 11 and a single fraction of 8 Gy were independent predictors for the development of an SAE. However, the definition of an event was much broader than in the current study. For instance, hospitalization due to pain at the irradiated site was considered an SAE, constituting 37% of all events. It is unlikely that the SINS can evaluate hospitalization due to pain and including it as an adverse event could potentially obscure the results.
In contrast to our study, Cunha et al.11 found an association between the components spinal alignment and lesion type on the occurrence of a VCF and Sahgal et al.10 found an association between spinal alignment, lesion type and vertebral body collapse on the occurrence of a VCF. The major difference is that these two studies reported on patients who underwent high-dose stereotactic radiotherapy, potentially resulting in more VCFs whereas the population in this study underwent relatively low-dose radiotherapy.
A limitation of the current study is the retrospective design. The SINS component pain was determined based on patient charts and intake forms, possibly resulting in inaccurate interpretation of the data. The availability of pretreatment CT scans was limited (236/1042, 23%), reducing the overall population count.
Although patients who presented with evident clinical spinal instability and were operated on are not represented in this study, our analysis reflects the more important daily clinical scenario. The main treatment for patients with painful bone metastases is radiotherapy. Since these patients have limited survival, spinal surgery must only be applied in case of a reasonable and stable clinical condition.
VII
SINS
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