MRI tumour regression grade 105 CHAPTER 6 Results Patients A total of 313 patients had a resection with curative intent for LRRC between 2010 and 2018, of whom 132 received induction chemotherapy followed by chemo(re)irradiation. Eight patients were excluded because no baseline or restaging MRI was available, resulting in 124 selected patients (Figure 1). Demographics, tumour characteristics and details about the treatment are shown in Table 1. Median interval between the end of chemoradiotherapy and surgery was 13 weeks [IQR: 11-15 weeks]. Median interval between post-chemoradiotherapy MRI and surgery was 7 weeks [IQR: 5-8 weeks]. With respect of the pathology assessment in patients with a good response (Mandard 1–2), in 32 of 39 cases (82 percent) at least one section per centimetre maximum tumour bed diameter was sampled, whereas in 5 patients (10 percent) this could not be reassessed due to incompleteness of the report, and in two patients less than one section per centimetre tumour diameter was sampled. Agreement mrTRG – pTRG There was a fair level of agreement (k = 0.30; 95 percent confidence interval [CI] 0.200.40) between the lead radiologist and the pathologist when using the five-tier grading system, and a moderate level of agreement (k = 0.52; 95 percent CI 0.36-0.68) when comparing good (mrTRG 1-2, Mandard 1-2) and intermediate/poor responders (mrTRG 3-5, Mandard 3-5). Table 2 shows the agreement between the radiologists and the pTRG using the two-tier grading systemand the five-tier grading system. Figure 2-6 showMRI imaging of cases in which the mrTRG assessment corresponded with the pTRG. Figure 2 and Figure 6 also show the corresponding histology images. Using the two-tier grading system, assessment of the agreement between pTRG and mrTRG in patients with a long interval between MRI and surgery (more than 7 weeks, n = 61) resulted in a fair agreement (k = 0.34, 95 percent CI 0.12-0.56), whereas the agreement was good in patients with a short interval (7 weeks or less, n = 63; k = 0.69, 95 percent CI 0.49-0.90). The five-tier system resulted in k values of 0.26 and 0.32 for long and short intervals respectively, and therefore seems less suitable for clinical use. When using the two-tier grading system, the lead radiologist underestimated the presence of residual tumour in 1 percent of the cases, correctly assessed the residual tumour in 82 percent and overestimated the presence of residual tumour in 17 percent of the cases.
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