153 A Summary In Chapters 5, 6 and 7 we focused on methods to assess and predict response to neoadjuvant chemoradiation (CRT). In Chapter 5, we investigated the value of rectal cancer T-staging on MRI after chemoradiotherapy (ymrT-staging) in relation to the degree of fibrotic transformation of the tumour bed. We found that MRI is has reasonable accuracy (mean 58%; up to 67% for expert radiologists) for yT-staging in poor responding patients with predominant solid tumour and limited fibrosis after CRT. In good responders who show predominant fibrosis, ymrT-staging is highly inaccurate (accuracy 41%) and results in substantial overstaging. These results suggest that in the latter subgroup ymrT-staging should perhaps be discarded completely from routine reporting. In Chapter 6 we investigated several other methods that have been developed in recent years to grade response on MRI after CRT. Twenty-two radiologists applied four different methods to grade response on the restaging MRIs of 90 rectal cancer patients, including two methods based on T2-weighted MRI only and two based on a combination of T2W-MRI and diffusion-weighted imaging (DWI). The methods including DWI showed the most favorable results when combining diagnostic performance, interobserver agreement and reader preference. The most preferred method (by 73% of readers) was the ‘DWI patterns’ approach with an accuracy of 68%, high specificity of 82% and group IOA of 0.43 to predict a complete response after CRT. We furthermore showed that the experience level of the radiologists and overall image quality of the MRIs both had a significant impact on diagnostic performance and interobserver agreement, emphasizing the importance of state-of-the-art imaging and dedicated training. In Chapter 7 the same twenty-two radiologists reviewed the baseline staging MRIs of the patients described in Chapter 6 to see if they could predict already at baseline – i.e. before the start of CRT – how well patients would respond to therapy. Three different visual scoring methods were compared to predict the likelihood that patient would undergo a (near) complete response; a previously published 5-point confidence score and two simplified (4-point and 2-point) adaptations. The diagnostic performance was comparable for the three methods (AUC 0.71-0.74), but IOA was higher for the 4- and 5-point scores. The 4-point risk score based on a combination of high risk cT-stage, MRF invasion, EMVI, and nodal involvement was selected as the preferred method by 55% of readers.
RkJQdWJsaXNoZXIy MjY0ODMw