Vanderbilt University School of Medicine.
Department of Radiation Oncology.
Otol Neurotol. 2020 Feb;41(2):e262-e267. doi: 10.1097/MAO.0000000000002488.
Accurate volume assessment is essential for the management of vestibular schwannoma after stereotactic radiosurgery (SRS). A cuboidal approximation for volume is the standard surveillance method; however, this may overestimate tumor volume. We sought to evaluate several volumetric models and their suitability for post-SRS surveillance.
Retrospective cohort study.
Tertiary referral center.
We evaluated 54 patients with vestibular schwannoma before and after SRS.
INTERVENTION(S): Gold-standard volumes were obtained by a radiation oncologist using contouring software. Volume was also calculated by cuboidal, ellipsoidal, and spherical formulae using tumor diameters obtained by a neuroradiologist.
MAIN OUTCOME MEASURE(S): Percent error (PE) and absolute percent error (APE) were calculated. Paired t test evaluated bias, and the Bland-Altman method evaluated reproducibility. Linear regression evaluated predictors of model error.
All models overestimated volume compared with the gold standard. The cuboidal model was not reproducible before SRS (p < 0.001), and no model was reproducible after SRS (cuboidal p < 0.001; ellipsoidal p = 0.02; spherical p = 0.02). Significant bias was present before SRS for the cuboidal model (p < 0.001), and post-SRS for all models [cuboidal (p < 0.001), ellipsoidal (p < 0.02), and spherical (p = 0.005)]. Model error was negatively associated with pretreatment volume for the cuboidal (PE p = 0.03; APE p = 0.03), ellipsoidal (PE p = 0.03; APE p = 0.04), and spherical (PE p = 0.02; APE p = 0.03) methods and lost linearity post-SRS.
The standard cuboidal practice for following vestibular schwannoma tumor volume after SRS overestimates size. Ellipsoidal and spherical estimations have improved performance but also overestimate volume and lack reliability post-SRS. The development of other volumetric models or application of contouring software should be investigated.
准确的体积评估对于立体定向放射外科（SRS）后前庭神经鞘瘤的管理至关重要。立方近似法是标准的监测方法，但可能会高估肿瘤体积。我们旨在评估几种体积模型及其在 SRS 后监测中的适用性。
回顾性队列研究。
三级转诊中心。
我们评估了 54 例前庭神经鞘瘤患者在 SRS 前后的情况。
由放射肿瘤学家使用轮廓软件获得金标准体积。还通过神经放射学家获得的肿瘤直径，使用立方、椭圆和球体公式计算体积。
计算百分比误差（PE）和绝对百分比误差（APE）。配对 t 检验评估偏差，Bland-Altman 方法评估可重复性。线性回归评估模型误差的预测因素。
与金标准相比，所有模型均高估了体积。在 SRS 前，立方模型不可重复（p<0.001），在 SRS 后，没有一个模型可重复（立方模型 p<0.001；椭圆模型 p=0.02；球体模型 p=0.02）。在 SRS 前，立方模型存在显著偏差（p<0.001），而在 SRS 后，所有模型均存在偏差[立方模型（p<0.001）、椭圆模型（p<0.02）和球体模型（p=0.005）]。在 SRS 前，立方模型的模型误差与预处理体积呈负相关（PE p=0.03；APE p=0.03），椭圆模型（PE p=0.03；APE p=0.04）和球体模型（PE p=0.02；APE p=0.03），在 SRS 后，这种线性关系丧失。
SRS 后，标准的立方体实践方法用于监测前庭神经鞘瘤肿瘤体积会高估肿瘤大小。椭圆和球体估计方法的性能有所提高，但也高估了体积，并且在 SRS 后缺乏可靠性。应研究其他体积模型的开发或轮廓软件的应用。
