Statistical analysis

The statistical analysis investigated the following aspects: calculation of diagnostic performance of conventional MRI and combined set of conventional MRI in addition to DWI (sensitivity, specificity, positive predictive value and negative predictive value); Hypothesis test - two-way ANOVA (Analysis of Variance) using two factors: staging (ranging from ypT0 to ypT4) and treatment status (pre- or post-CRT) with Bonferroni test post-hoc; Student t-test for comparison after normality test; Correlation between post-CRT ADC values and final T staging with Spearman correlation; Gaussianity tests and the estimation of a Gaussian distribution of post-CRT ADC.

Statistical analyzes were performed using the t and ANOVA tests, conducted with Epi Info software (version 3.3.2, Control Diseases Center, Atlanta, GA, USA). The receiver operating characteristics (ROC) curves were used to analyze the different cutoff values, aiming at the point of highest sensitivity and specificity to the differentiation between pCR and non-pCR. The analyzes of ROC curves and the gaussianity tests were performed using SPSS for Windows (version 10, IBM SPSS, Chicago, IL, USA). Estimates of power analysis were calculated for each sample using Stata software version 8.2 (Stata, College Station, TX, USA). The study had a 95% confidence level (α = 0.05), and the value of p ≤ 0.05 determined the significance in all tests.