Desley van Zoggel

Chapter 8 148 If tumour response will become a decisive factor in the management of LRRC, monitoring for tumour response will be the cornerstone of treatment planning at MDT meetings. After primary surgery postoperative changes will confront the radiologist with the difficulty to discriminate tumour recurrence from postoperative fibrosis. Furthermore evaluating tumour regression can be difficult to assess in the presence of abundant fibrosis. At the CHE MRI was used since 1994 to stage the topographical relation to surrounding tissue and structures. The resolution of MRI in soft tissue cannot be matched by CT. The accuracy to stage soft tissue infiltration is nearly 100 percent.18 MRI is the basis of classification of LRRC. Two recent reviews confirmed the role of accurate soft tissue imaging for classification and making results from different institutes comparable.19,20 Radiomics like diffusion-weighted imaging (DWI) may become more important in response monitoring. Especially in surveying primary rectal cancer, who entered a watch and wait protocol.21 However the added value of DWI in the assessment of LRRC is more limited.22 In chapter 6 mrTRG is compared to downstaging according the pathology of the final specimen. The accuracy and the interobserver variation even in a highly specialized centre is limited.23 PET/CT which looks at metabolic changes may be complementary to the anatomical local staging of MRI. In chapter 7 the evaluation of tumour response in LRRC after intensified preoperative treatment with ICT was investigated. A correlation between response on PET/CT and Mandard score of the pathologic specimen was found. Even more important was the finding that response and the probability of achieving a clear resectionmarginwas significantly correlated in a linear fashion: themore response, the higher the clear resectionmargin rate. PET/CT response was complementary to mrTRG as assessed with MRI.24 However, limitations do exist: especially timing of PET/CT is important. Waiting longer than 6 to 7 weeks between response evaluation and surgerymakes the assessment unreliable. Response can go further, but progression is also possible. This finding was also true for MRI response evaluation. Repeated imaging will probably be the answer. Overall response evaluation in LRRC patients is far more difficult than in primary rectal cancer patients.