Diffusion and Perfusion MR Parameters in Locally Advanced Rectal Cancer Management: An Explorative Study

Abstract

Background: Diffusion Weighted (DW) and Dynamic Contrast Enhanced (DCE) MRI have been used in therapy assessment of several tumors. Purpose: The aim of this paper is to explore the possibility to apply DW- and DCE-MRI in Locally Advanced Rectal Cancer (LARC) to predict complete pathological response (CPR) to short-course radio-therapy (SCRT). Methods: 34 patients with LARC underwent DCE and DW-MRI before and after SCRT. Afterwards, patients were surgically treated. Pathological responses were registered. Tumor Regression Grade (TRG) on a scale from 1 to 5 on the surgical sample was used to classify the response. Two groups (CPR = 1 complete pathological response and CPR = 0 partial response) were identified. The discriminative power of several features from DW and DCE MRI has been investigated. Specifically, diffusion features from the intra-voxel incoherent motion (IVIM) model have been computed by means of Siemens MR Body Diffusion ToolBox; in addition, diffusion kurtosis parameters have been estimated. As regards DCE features, we used the Standard Index of Shape (SIS) which our group has proposed in previous works. DW features and SIS have been evaluated on a statistical basis (Wilcoxon-Mann-Withney test for two independent samples, Area Under Curve of Receiver Operating Characteristics). Results: All diffusion features showed a significant variation after therapy; however, this difference was not significant to predict complete response. SIS was the only feature to show statistical significant difference between the two groups. ROC and tree-based analysis revealed an optimal cut-off of $78.26$ with specificity and sensitivity of $0.93$ and $0.86$ respectively.