158 Appendices Regarding the assessment of response of rectal tumours to chemoradiation, we identified in Chapter 5 as an important pitfall that MRI is not accurate for yT staging in patients who respond very well and show predominant fibrosis after CRT. In these patients yT-stage accuracy on MRI is less than 50% and results in major overstaging. These results suggest that in this subgroup yT-staging should perhaps be abandoned all together and we need to look for alternative ways to assess the local tumour response. In Chapter 6 we found that methods designed to grade response that incorporate the findings of diffusion-weighted imaging (DWI) showed the most favorable results. Additionally, we found that experience level of the radiologists performing the assessments, as well as image quality both had a significant impact on the performance on these restaging methods, stressing the importance of high-quality image acquisition and dedicated radiologist training. In Chapter 7 we found encouraging results for visual assessment of MRI to predict response already at baseline, i.e. before the start of treatment. However, the predictive performance of MRI was not sufficient (yet) to guide clinical decision making and should probably be combined with other clinical, histopathological, immunohistochemical and genetic predictors of response. Finally, in Chapter 3 we showed that our iScore webplatform also offers unique opportunities as a support tool for virtual training and teaching. Exploratory results of a virtual hands-on training program combining individual case-based training with webinars and online expert-teaching showed an overall increase in diagnostic staging performance with corresponding improved interreader reproducibility and staging confidence. These results suggest that dedicated virtual training programs can be a good alternative or addition to face to face training. Relevance The findings of this thesis are relevant for radiologists and other clinicians involved in the management of rectal cancer, but can also be extended to other clinical settings. With this thesis, we offer diagnosticians and other clinicians with the tools to set up international studies to properly evaluate and validate (visual) diagnostic methods. The use of iScore in such a way can be translated to other clinical questions, as well as beyond the field of colorectal cancer. Moreover the iScore webplatform and research infrastructure creates new opportunities for training and teaching (as demonstrated in Chapter 3), which is beneficial in promoting effective clinical dissemination and implementation of study outcomes. With respect to rectal cancer we have learned from Chapters 2 and 3 that despite efforts to standardize the radiological staging of rectal cancer there are still certain pitfalls that should be accounted for in future guideline and template updates and for which dedicated (online) teaching can be of added value. The importance of experience level
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