A Comparison of Diagnostic Performance of Signal Intensity and Volume Related MRI Multiparameters for Assessing Different Response of Rectal Cancer to Neoadjuvant Chemoradiotherapy

Abstract

Background: “Wait-and-see”, has been proposed as a possible method of treatment in patients with locally advanced rectal cancer (LARC) after chemoradiotherapy (CRT), MR is important to predict the pathological tumor regression grade(TRG) to preoperative CRT. This study aims to evaluate the diagnostic value of signal intensity (SI) and volume (V) change rate in magnetic resonance imaging (MR) and determine which ones perform best as a potential biomarker for predicting pathological TRG to preoperative CRT in patients with LARC.Methods: A retrospective analysis of 82 patients with LARC, for whom clinical and imaging data were retrieved from our institute was conducted between Oct 2017and Oct 2019. Patients underwent pre- and post-CRT T2-weighted (T2W), diffusion-weighted (DW)/apparent diffusion coefficient (ADC) and contrast-enhanced T1-weighted (ceT1W). V, difference of volume between pre-CRT and post-CRT tumor (△V), V of tumor reduction rate (%△V), as well as SI of tumor (SIt), SI of muscle (SIm), relative SI ratio of tumor/muscle (SIR), changed difference SIR between pre- and post-CRT SIR (△SIR), SIR of tumor changed rate (%△SIR) on T2W, ADC and ceT1W were measured. All of LARC after CRT were confirmed pathologically and classifed into histologic TRG: TRG 0 (complete response), TRG 1 (moderate response), TRG 2 (minimal response), TRG 3 (poor response). Descriptive statistics and areas under the receiver operating characteristic curves (ROC) were generated to compare performance of %△V and %△SIR on T2W, DW, ceT1W for distinguishing between different pathological TRG.Result: Of the 82 patients, TRG 0 (16), TRG 1 (15), TRG 2 (35), TRG 3 (16).Except for ADC-%△SIR, the remaining %△V and %△SIR on T1W, ADC/DWI, ceT1W showed statistics significance between four groups. There was not distinguishable between TRG 1 and TRG 2, TRG 2 and TRG 3 by %△V and/ or %△SIR, the remaining different TRG all were identified by %△V and/ or %△SIR on T2W, ADC/DWI, ceT1W. Compared with other individual %△V or %△SIR, the combination of DW-%△V and T2W-%△SIR (DW-%△V * T2W-%△SIR) yielded higher AUCs to predict TRG 0 from TRG 2 (AUCs: 0.954, sensitivity: 93.75%, specificity: 97.14%) and TRG 3 (AUCs: 1.000, sensitivity: 100%, specificity: 100%), although AUC of all had not significant differences between TRG groups. there was statistically significant differences in post-CRT T restage and ypT stage between fours groups, respectively, but the agreement between post-CRT T restage and ypT is low ( kappa=0.191).Conclusions: V and/or SIR change rate on T2W, DW, ceT1W with high diagnostic performance could be useful in differentiating complete response from non-complete response; SIR change rate could be useful for distinguishing between moderate response and poor response.