127 Predicting response to chemoradiotherapy in rectal cancer via visual morphologic assessment and staging on baseline MRI 7 Table 5 Reader preference Difficulty to apply method (%)* 5-point confidence score 4- point risk score 2-point risk score Easy 52% 69% 74% Moderate 40% 30% 21% Difficult 7% 2% 5% Preferred method (%)** 27% 55% 18% * Scored for each individual case (percentages represent the average scores for all cases and readers combined) ** Scored once, after completion of all study cases (percentages represent the average scores for all readers combined). Discussion With this study we investigated the value MRI to estimate the chance that patients will undergo a (near-)complete response to neoadjuvant chemoradiotherapy based on visual morphologic risk assessment and staging performed on baseline MRI. A previously published 5-point confidence score and two simplified (4-point and 2-point) adaptations were tested and compared in terms of diagnostic performance, interobserver reproducibility, and reader preference. Diagnostic performance to predict a (near-)complete response was similar for the three methods with AUCs ranging between 0.71 and 0.74. When also considering interobserver agreement and reader preference, a 4-point risk score based on a combination of high risk T-stage, MRF invasion, EMVI, and nodal involvement showed the most favorable results. Interobserver agreement in our study was at best moderate (α=0.46-0.57), with somewhat better results for the MRI-experts, especially for the 4- and 5-point scores (α=0.64-0.65). The more expert radiologists also showed a tendency towards better diagnostic performance, albeit that the difference in performance did not reach statistical significance in most cases. IOA for the most simplified 2-point risk score was similarly low for the experts and non-experts (α=0.44-0.47). The previously published confidence score proposed by van Griethuysen is a relatively complex composite score that incorporates T-stage, size, signal, shape, N-stage, EMVI, and MRF involvement. We hypothesized that by simplifying this score, we might be able to improve interreader reproducibility. However, such an effect was not observed. Nevertheless, most readers did show a clear preference for the simplified scoring systems – in particular the 4-point risk score – and indicated that they found this method more straightforward to apply. This scoring system may therefore be more easy to adapt in daily practice, especially by more general readers.
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