Chapter 6 114 as well as diffusion-weighted imaging (DWI) might be able to reduce overstaging and consequently improve the selectionof complete responders. AlthoughDWI has a greater vulnerability to susceptibility artefacts and careful interpretation of T2 shine-through effect is required, it has proven to improve the sensitivity of the mrTRG score without decreasing the specificity in restaging LARC.19–21 Such a combined grading system has recently been proposed in patients with LARC and could be the focus of future research in LRRC.22 The interval between MRI and surgery may also play an important role in over- and understaging. As shown in this study, the agreement between mrTRG and pTRG was superior in cases with an interval ≤7 weeks compared to the agreement in cases with an interval >7weeks. This is consistent with previous studies that showed, in LARC, that a shorter interval betweenMRI and surgery resulted in a stronger association between themrTRG and pTRG.23 The length of the interval may particularly play a role inmrTRG 3 cases. In these cases, a long interval may provide an opportunity for a continuation of response, or, although rare, progression of disease. Ideally, mrTRG should therefore be assessed shortly before surgery. The interobserver variability between the radiologists was moderate (k = 0.50) when using the five-tier grading, which is comparable with what was found in a study performed under 35 radiologists assessing themrTRG in patients with LARC.1 However, when using the two-tier regression scale, the agreement was only fair. This indicates a suboptimal reproducibility of the mrTRG. The level of agreement between the lead radiologist and the pTRG and the second radiologist and the pTRG, and the other abdomen radiologist and the pTRG differed: the agreement was moderate for the lead radiologist, whereas this was fair for the other abdominal radiologist. Although both are experienced abdominal radiologists, the lead radiologist has specific expertise in LARC and LRRC and is themain radiologist responsible for theweeklyLARC/LRRCMDTmeeting. Thepresenceof anMDT is crucial in the treatment of patients with colorectal cancer, as it improves their outcome.24 Moreover, MDT discussion improves the accuracy of MRI in staging rectal cancer.25–27 It is reasonable to assume thatmore intensive involvement of the radiologist in the LARC/ LRRCMDT improved the accuracy of the restaging assessments. For example, through participation in the MDT, the radiologist receives feedback from the discussion of the pathology of postoperative patients, strengthening the learning curve. Thismay explain the difference in agreement, in favour of the lead radiologist. Additionally, refining the definitions of the categories of tumour regression, especially in mucinous and fibrotic tumours, may contribute to improving the radiologist’s performance.
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