基于改进的全卷积网络模型预测局部进展期直肠癌新辅助放化疗疗效

  目的  建立基于MRI影像图像预测局部进展期直肠癌(locally advanced rectal cancer，LARC)新辅助放化疗(neoadjuvant chemoradiotherapy，nCRT)后病理学完全缓解(pathological complete response，pCR)模型，以辅助患者个性化治疗方案的制订。  方法  回顾性纳入2013年6月至2018年12月中山大学附属第六医院接受nCRT治疗且行全直肠系膜切除术组织病理对治疗效果进行评定的LARC患者。按1:2的比例将患者依照住院时间先后顺序分为Data A与Data B 2个数据集。其中Data A数据集用于语义分割模型训练，Data B数据集按7:3的比例随机分为训练集和验证集，分别用于pCR预测模型训练与评价。收集Data A数据集病例的T2加权MRI影像资料，采用改进的全卷积网络(fully convolutional networks，FCN)模型对肿瘤区域进行语义分割，建立语义分割模型并提取最终卷积层中的影像特征。采用最小绝对值收缩和选择算子(least absolute shrinkage and selection operator, LASSO)回归法对提取的影像特征进行筛选，构建可预测pCR状态的支持向量机(support vector machine，SVM)分类器(预测模型)。以Data B训练集数据为基础，对该预测模型的性能进行训练，进一步在Data B验证集中对其性能进行评价。  结果  共入选符合纳入和排除标准的LARC患者304例，nCRT治疗后82例判定为pCR，222例为非pCR。2013年6月至2015年11月的103例患者为Data A数据集，2015年12月至2018年12月的201例患者为Data B数据集。Data B数据集中，训练集140例、验证集61例。改进的FCN模型对Data B数据集图像分割的Dice值为0.79 (95% CI: 0.65~0.81)，灵敏度为80%(95% CI: 77%~83%)，特异度为72%(95% CI: 64%~85%)。语义分割模型共提取最终卷积层中512个影像特征，经LASSO回归筛选后保留7个，用于pCR状态预测。预测模型在Data B训练集中预测pCR的曲线下面积(area under the curve, AUC)为0.65(95% CI: 0.61~0.71)，在Data B验证集中的AUC为0.69(95% CI: 0.59~0.74)。  结论  本研究提出的改进的FCN模型，对MRI图像进行语义分割具有较高的准确度。基于该方法构建的模型预测LARC患者接受nCRT治疗后pCR状态具有可行性。

Prediction of Survival Status of Locally Advanced Rectal Cancer after Neoadjuvant Chemoradiotherapy Based on Improved Fully Convolutional Networks Model

  Objective  To explore the model of using after neoadjuvant chemoradiotherapy (nCRT) imaging images of locally advanced rectal cancer (LARC) to predict whether pathological complete response (pCR) is achieved, thereby assisting physicians to develop a personalized plan.  Methods  Patients with LARC treated with nCRT at the Sixth Affiliated Hospital of Sun Yat-sen University from June 2013 to December 2018 were retrospectively included, and the treatment outcome was evaluated by total rectal mesenteric resection histopathology. The patients were divided into 2 data sets, Data A and Data B, according to the order of hospitalization time in a ratio of 1:2. Data A was used for semantic segmentation model training, and Data B was randomly divided into training and validation sets in the ratio of 7:3, which were used for pCR prediction model training and validation, respectively. The T2-weighted MRI images of Data A were collected, and the improved fully convolutional networks(FCN) model was used to semantically segment the tumor region, establish the semantic segmentation model and extract the image features in the final convolutional layer. The least absolute shrinkage and selection operator (LASSO) regression model was used to filter the extracted image features and construct a support vector machine (SVM) classifier that could predict the pCR state. The performance of the prediction model was trained on the basis of the Data B training set and further validated in the Data B validation set.  Results  A total of 304 patients with LARC who met the inclusion and exclusion criteria were enrolled, 82 patients reached pCR after nCRT, while 222 patients did not reach pCR (non-pCR). Among them, 103 patients from June 2013 to November 2015 were in Data A and 201 patients from December 2015 to December 2018 were in Data B. In Data B, 140 patients were in the training set and 61 patients in the validation set. The improved FCN model had a Dice value of 0.79(95% CI: 0.65-0.81), a sensitivity of 80%(95% CI: 77%-83%), and a specificity of 72%(95% CI: 64%-85%). A total of 512 image features in the final convolutional layer were extracted by the semantic segmentation model, and 7 were retained after LASSO regression screening for pCR state prediction. The area under the curve of the prediction model was 0.65(95% CI: 0.61-0.71) in the Data B training set and 0.69(95% CI: 0.59-0.74) in the Data B validation set for predicting pCR.  Conclusions  The improved FCN model proposed in this study has high accuracy for semantic segmentation of MRI images. The prediction model constructed based on this method is feasible to predict pCR status of LARC patients after receiving nCRT treatment.