MRI tumour regression grade 115 CHAPTER 6 This study has several limitations. mrTRGwas only assessed by two radiologists. Ideally, this assessment would have been performed by a larger group. However, LRRC is rare and surgical treatment is centralized in only a small number of tertiary referral centres, and even in these centres the radiological expertise is usually limited to one or two radiologists. In addition, the interval between theMRI and surgerywas long, whichmay have negatively influenced the agreement. Moreover, although pathologic assessment is the gold standard for determining response and Mandard provides a high accuracy in predicting prognosis, variable reproducibility has been reported.28,29 The strength of this study is that this is the first study assessing the mrTRG in patients with LRRC. Moreover, the size of this homogenous cohort of LRRC patients is unique with a large series of patients analysed. According to the present results, mrTRG can predict a good response after neoadjuvant treatment with chemotherapy and chemoradiotherapy for LRRC when assessed by an experienced, dedicated and trained radiologist. However, the reproducibility of the mrTRG between radiologists is limited and the agreement between mrTRG and pTRG is low in cases with a long interval between MRI and surgery. Therefore, mrTRG cannot simply be used as a predictor for pTRG and treatment decision making during theMDT cannot yet be based on themrTRG. Further studies are needed to evaluate the optimal timing of the MRI, the prognostic value of mrTRG, and the value of mrTRG in combination with other imaging modalities such as PET/CT in LRRC.