基于高分辨T2加权图像的影像组学模型评估局部进展期直肠癌新辅助放化疗效果的应用分析

Application analysis of radiomics models based on high-resolution T2-weighted MR images for evaluating the effectiveness of neoadjuvant chemoradiotherapy in locally advanced rectal cancer

目的探讨基于高分辨T2加权图像的影像组学模型评估局部进展期直肠癌新辅助放化疗效果的效能。方法回顾性收集2018年1—12月于海军军医大学第一附属医院接受治疗的局部进展期直肠癌患者的临床资料,患者接受新辅助放化疗(长程放疗联合同步化疗)且术后病理证实为直肠腺癌。患者完成基线和新辅助放化疗之后的直肠高分辨T2加权序列扫描,由放射科医师根据新辅助放化疗之后的高分辨T2加权图像的裂隙瘢痕征进行新辅助放化疗效果的主观评价。以术后病理肿瘤退缩分级作为评估新辅助放化疗效果(疗效良好或疗效不良)的“金标准”。在基线和新辅助放化疗之后的高分辨T2加权图像上勾画感兴趣区,自动生成容积感兴趣区。以两种方式提取影像组学特征并相应建模:Model 1,从基线容积感兴趣区提取影像组学特征;Model 2,从新辅助放化疗之后的容积感兴趣区提取影像组学特征。选择组内相关系数≥0.8的特征,采用最小绝对收缩与选择算子算法进行降维,选择用于评价肿瘤退缩分级的最佳相关影像组学特征。随机选取70%的病例作为训练集构建XGBoost模型(Model 1和Model 2),剩余30%的病例作为测试集对两个模型分别进行验证。分别针对影像组学模型和裂隙瘢痕征主观评价的结果绘制受试者工作特征曲线并进行分析(曲线下面积、曲线下面积的95%置信区间、敏感度、特异度、准确率、精准率、F1值)。采用Delong检验、计算净重新分类指数比较组间差异。采用决策曲线分析方法评估临床获益。结果纳入189例患者的临床资料进行分析,其中新辅助放化疗结束与手术治疗的中位时间间隔为68(63,74)d,新辅助放化疗之后的直肠高分辨T2加权序列扫描与手术治疗的中位时间间隔为6(4,9)d,达到病理完全缓解者41例,根据术后病理肿瘤退缩分级评价为疗效良好者93例,占比为49.2%。Model 1、Model 2分别获取8个、6个最佳相关影像组学特征。测试集中,Model 1、Model 2的曲线下面积分别为0.977(95%置信区间为0.955~1.000)、0.921(95%置信区间为0.865~0.978),裂隙瘢痕征主观评价的曲线下面积为0.633(95%置信区间为0.540~0.727)。Delong检验结果显示,Model 2与Model 1相比,P=0.186;Model 2与Model 1相比,净重新分类指数为-0.402。Delong检验结果显示,裂隙瘢痕征主观评价与Model 1、Model 2相比,P值均小于0.05;裂隙瘢痕征主观评价与Model 1、Model 2相比,净重新分类指数均为负值。决策曲线分析结果显示,在0~1的概率阈值范围内,Model 1和Model 2的临床获益优于将所有患者视为疗效良好或疗效不良,也优于裂隙瘢痕征主观评价,而且Model 1的临床获益优于Model 2。结论基于基线和新辅助放化疗之后的高分辨T2加权图像所建立的影像组学模型均可以较为有效地评估局部进展期直肠癌的肿瘤退缩程度,而且基于基线图像的影像组学模型的评估效能相对更优。

Objectives To explore the efficacy of radiomics models based on high-resolution T2-weighted MR images(HRT2WI)in evaluating the effectiveness of neoadjuvant chemoradiotherapy(nCRT)in locally advanced rectal cancer(LARC).Methods We retrospectively collected clinical data of patients with LARC who were treated at the First Affiliated Hospital of Naval Medical University from January to December 2018.The patients received nCRT(long-term radiotherapy combined with concurrent chemotherapy)and were confirmed to have rectal adenocarcinoma by postoperative pathology.High-resolution T2-weighted MR imaging of the rectum was performed in baseline status and after nCRT.Subjective evaluations of the effectiveness of nCRT was performed by radiologists based on the presence of split scar sign(SSS)on HRT2WI after nCRT.The postoperative pathological tumor regression grade(TRG)was used as the"gold standard"for evaluating the effectiveness of nCRT(good or poor outcomes).Region of interest was delineated on HR-T2WI in baseline status and after nCRT,and a volume of interest(VOI)was automatically generated.Radiomics features were extracted in two ways and corresponding models were built:Model 1 extracted radiomics features from baseline VOI;Model 2 extracted radiomics features from VOI after nCRT.Features with an intraclass correlation coefficient≥0.8 were selected,and the least absolute shrinkage and selection operator were used for dimensionality reduction to select the optimal relevant radiomics features for evaluating TRG.Seventy percent of the cases were randomly selected as the training set to construct the XGBoost models(Model 1 and Model 2),and the remaining 30%of the cases were used as the test set to validate the two models separately.Receiver operating characteristic curves were plotted and analyzed for the results of the radiomics models and subjective evaluations of SSS[area under the curve(AUC),95%confidence interval(CI)of the AUC,sensitivity,specificity,accuracy,precision,F1 score).The Delong test and calculation of the net reclassification index(NRI)were used to compare differences between models.Decision curve analysis(DCA)was used to assess clinical benefits.Results The clinical data of 189 patients were included in the analysis.The median time interval between the end of nCRT and surgical treatment was 68(63,74)days,and the median time interval between high-resolution T2-weighted MR imaging of the rectum after nCRT and surgical treatment was 6(4,9)days.Forty-one patients achieved pathological complete response,and 93(49.2%)patients were evaluated as having good outcomes based on the postoperative pathological TRG.Eight and six optimal relevant radiomics features were obtained for Model 1 and Model 2,respectively.In the test set,the AUC for Model 1 and Model 2 were 0.977(95%CI:0.955-1.000)and 0.921(95%CI:0.865-0.978),respectively,while the AUC for subjective evaluations of SSS was 0.633(95%CI:0.540-0.727).The Delong test showed that compared with Model 1,P=0.186 for Model 2,and the NRI for Model 2 compared with Model 1 was-0.402.The Delong test also showed that subjective evaluations of SSS was significantly different from Model 1 and Model 2,with P values less than 0.05,and the NRI for subjective evaluations of SSS compared with Model 1 and Model 2 was negative.The results of DCA indicate that within the probability threshold range of 0 to 1,the clinical benefits of Model 1 and Model 2 are superior to considering all patients as having good or poor outcomes,as well as superior to subjective evaluations of SSS.Furthermore,the clinical benefits of Model 1 are superior to that of Model 2.Conclusion Both the radiomics models based on HR-T2WI in baseline status and after nCRT can effectively evaluate the degree of tumor regression in LARC,with the radiomics model based on baseline images exhibiting relatively better performance.