The focus of this study was to clarify the value of manual tumor %△V, %△SIR and combined of their estimations obtained by T2W, DWI, ceT1W for predicting TRG after CRT in the patients with LARC, and results show that good diagnostic performance of T2W-%△V, DW-%△V, ceT1W-%△V, T2W-%△SIR, ceT1W-%△SIR, and DW-%△V * T2W-%△SIR for discriminating TRG 0 from TRG 2 and TRG 3, T2W-%△V, DW-%△V, ceT1W-%△V for TRG 0 and TRG 1, T2W-%△SIR, ceT1W-%△SIR for TRG 1and TRG 3; despite there was no statistical difference in AUC of all ROC, DW-%△V * T2W-%△SIR had highest AUC; but all measurement of V and SIR were not helpful for distinguishing between TRG 1 and TRG 2, TRG 2 and TRG 3. To the best of ourknowledge, no prior studies have comprehensively assessed and compared the performances of V change rate and SIR volume change rate on T2W, DWI, ceT1W to predict different grade response after CRT.
In present study, agreement of post-CRT MR T restaging and pathological ypT stagewas low (Kappa = 0.191), this is consistent with the results of some prior studies[3, 4, 8]. Tumor volume and signal intensity has been proven to be an important prognostic indicator for achange of tumors during CRT and response of after CRT. Van den et al and Doenja et al reported changes in rectal tumor morphology (fibrosis) and volume visually evaluated can already be observed during CRT[11, 16]. Volume was reported to correlate well with downstaging of rectal cancer[14, 25], and Lambregts et al reported post-CRT DWI volumetry offers the best results for the detection of patients with a CR after CRT with an area under the curve of 0.92, sensitivity of 70%, and specificity of 98%. In line with previous studies, volume has good diagnostic performance discriminating TRG 0 from TRG 1, TRG 2 and TRG 3 with AUC of 0.921 ~ 0.984, sensitivity of 75 ~ 93.75%, and specificity of 85.71 ~ 100%.
Hotker el al reported tumour volumetry on post-treatment DCE-MRI and DW-MRI correlated well with histopathological percent tumour regression in the resected specimen, and was superior to post-CRT T2 tumour volumetry. In present study show diagnostic performance of volume on DW was slightly greater than T2W and ceT1W, but no statistic difference between AUC of which parameters; because on DW images, viable tumor remnants are more easily recognized, as they appear hyperintense compared with the low signal intensity (SI) of the surrounding non neoplastic tissue, which is in contrast with previous studies showed post-CRT DW MR volumetry with AUC of 0.93 provided high diagnostic performance in assessing CR and was significantly more accurate than T2-weighted MR volumetry.
Tumour volume may not or slightly change for poor response after CRT, but may had a fibrotic transformation that was unidentified by visual in tumor. Signal intensity rate on MR parameter by quantitative as monitoring therapy response after CRT and diagnostic value for tumor characterization and differentiation[19–21, 27]. Wan et al reported T2WI signal intensity related parameters with AUC of 0.694 ~ 0.762, sensitivity of 68.2%~77.3%, specificity of 63.6%~77.0 are potential predictors for pCR in LARC after CRT; Value of intra-tumor heterogeneity evaluated by DW for predicting TRG to CRT in lower rectal and measurements of ADC change induced by CRT may have considerable diagnostic value for the estimation of CR, was reported[27, 28]. DCE-MRI in rectal cancer is promising mainly for prediction and assessment of response to CRT. Our results are in contrast with previous studies, %△SIR on T2W, ceT1W is a promising diagnostic tool for CR and non-CR, TRG 1 and TRG 3, respectively. Our ADC-%△SIR results show useless, and this discrepancy in published data is probably due to the use of variety protocols, different ROI selection, and general factors contributing to magnetic field inhomogeneity suchas pH, hydration status, and susceptibility effects[27, 28, 30, 31].
In previous study, SIR and V on MR sequence was used to discriminate pCR or response groups from non-pCR or non response groups, and not for discrimination between TRG groups[2, 3, 8, 9, 12, 16, 18, 27, 28, 31]. In our study, SIR and V change rate on T2W, DW/ADC, ceT1W first were evaluated to differentiate different response grade after CRT, and considerable results were obtained that T2W-%△V, DW-%△V, ceT1W-%△V, T2W-%△SIR, ceT1W-%△SIR, and DW-%△V * T2W-%△SIR has higher diagnostic performance with accuracy of 82.35%~100% to predict TRG after pCRT compared to previous result[2, 9, 11–16, 23, 25, 27–29], except ceT1W for TRG 0 and TRG2; and among of all, despite that was no statistical difference, DW-%△V * T2W-%△SIR was highest for TRG with AUCs of 0.954 ~ 1.000, sensitivity of 93.75%~100%, specificity of 97.14 ~ 100%, accuracy of 96.08%~100%. %△V and %△SIR not distinguished TRG 1and TRG 2, TRG 2 and TRG 3, which could be due to that volume and fibrotic transformation of tumor for grade close to grade has little change or there was a ROI selection deviations after CRT. Volume be able to distinguish TRG 0 and TRG 1, which could be due to that ROI area from TRG 0 smaller than ROI area from TRG 1 which in addition to the tumor bed, volume for ROI containa little tumor.
Despite the interesting findings, our study has some limitations. First, This was a retrospective study with asmall sample size between TRG groups, which may limit the statistical power and generate a statistical bias. Further validation may be needed by prospective study withlarge sample size to prove our hypothesis. Second, Although all data need to be collected using the same type of MRI and protocol, it was not possible to unify our data because they were obtained from multiple MR unit. Unfortunately, intraobserver and interobserver differences were not evaluated, but SIR, △SIR, △V, %△ and %△SIR on MR sequence of preoperative after CRT for prediction TRG were calculated so as to reduce variability of imaging[2, 14, 27]. Reproducibility of relative SI is relative better than SI on MR sequence was reported[2, 13, 15, 19–21, 30, 31]. Hotker et al reported DCE-MRI volumetry demonstrating better inter-reader agreement. Third, select of ROI and comparison of MR before and after CRT had subjectivity; to overcome these issues, we evaluated a relatively largest area of cancerous tissue. Blazic et al reported the use of single-section and whole-tumor volume methods had similar accuracy in predicting CR based on post-CRT measurement ADC change and saved time compared to whole-tumor volume methods.