19 Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI 2 reference. The two experts staged the cases independently. In case of any disagreement, a third independent expert (ML, with similar >10 years of dedicated experience in rectal MRI) was consulted to reach final expert consensus. IOA and diagnostic accuracy (= agreement with the expert reference) were calculated for the 21 study readers. For staging items 3, 5, 8, 9, 15 (see Table 1) confidence scores were dichotomized to calculate diagnostic accuracy with the cut-off between equivocal and probably involved/positive. Polychoric correlation coefficients were calculated between the various confidence level scores and diagnostic accuracy. Pearson’s Chi-squared test was used to calculate p-values. The level of significance was set at p<0.05. Table 1 Staging variables derived from the ESGAR structured reporting template that were included in the electronic case report form in iScore Main staging variables used for risk stratification Variable Answer options Categorical 1 cT-stage - cT0, cT1-2, cT3, cT4a, cT4b - Level of confidence: very unconfident, unconfident, equivocal, confident, very confident 2* In case of cT3 tumour, cT3 sub-stage - cT3ab (≤5 mm extramural invasion depth), cT3cd (>5 mm extramural invasion depth) - Level of confidence: very unconfident, unconfident, equivocal, confident, very confident 3 Dichotomous cT-stage classification - Definitely low risk (cT1-2-3ab) - Probably low risk (cT1-2-3ab) - Equivocal (possibly low risk, possibly high risk) - Probably high risk (cT3cd-4ab) - Definitely high risk (cT3cd-4ab) 4 cN-stage - cN0 (no suspicious nodes), cN1 (1-3 suspicious nodes), cN2 (≥ 4 suspicious nodes) 5 Dichotomous cN-stage classification - Definitely cN0 - Probably cN0 - Equivocal (possibly cN0, possibly cN+) - Probably cN+ - Definitely cN+ 6 Lateral nodes - Yes, presence of ≥1 suspicious lateral lymph node(s) - No, absence of suspicious lateral lymph nodes 7 Tumour deposits - Yes, presence of ≥1 tumour deposit(s) - No, absence of tumour deposits 8 MRF involvement - Definitely MRF- (tumour-MRF distance > 1 mm) - Probably MRF- (tumour-MRF distance > 1 mm) - Equivocal (possibly MRF-, possibly MRF+) - Probably MRF+ (tumour-MRF distance ≤1 mm) - Definitely MRF+ (tumour-MRF distance ≤1 mm)
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