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Aim: To investigate the potential role of an additional magnetic resonance imaging (MRI) examination performed during neoadjuvant chemoradiation therapy (CRT) in the prediction of pathological response in locally advanced rectal cancer (LARC). Material and methods: Forty-eight consecutive patients with LARC underwent neoadjuvant CRT. MRI studies at 1.5 T, including high-resolution T2-weighted sequences that were acquired parallel and perpendicular to the main axis of the tumour were performed before (preMRI), during (midMRI), and 6-8 weeks after the end of CRT (postMRI). Cancer volumes (Vpre, Vmid, Vpost) were drawn manually and the reduction rate calculated (ΔVmid, ΔVpost). According to Rödel's pathological tumour regression grade (TRG), patients were considered non-responders (NR; TRG0-2), partial responders (PR; TRG3), and complete responders (CR; TRG4). Multivariate regression analysis was performed to identify the best MRI predictors of NR, PR, and CR. Results: Twenty-five patients were considered PR (52%), 13 CR (27%), and 10 NR (22%). Tumour shrinkage mainly occurred shortly after CRT (ΔVmid: CR: 80±10% versus PR: 56±19% versus NR: 28±22%, p=2.2×10-16). Vmid, Vpost, ΔVmid, and ΔVpostcorrelated with TRG (p

AIM To investigate the role of diffusion-weighted imaging (DWI), T2-weighted (W) imaging, and apparent diffusion coefficient (ADC) histogram analysis before, during, and after neoadjuvant chemoradiotherapy (CRT) in the prediction of pathological response in patients with locally advanced rectal cancer (LARC). MATERIALS AND METHODS Magnetic resonance imaging (MRI) at 1.5 T was performed in 43 patients with LARC before, during, and after CRT. Tumour volume was measured on both T2-weighted (VT2W) and on DWI at b=1,000 images (Vb,1,000) at each time point, hence the tumour volume reduction rate (ΔVT2W and ΔVb,1,000) was calculated. Whole-lesion (three-dimensional [3D]) first-order texture analysis of the ADC map was performed. Imaging parameters were compared to the pathological tumour regression grade (TRG). The diagnostic performance of each parameter in the identification of complete responders (CR; TRG4), partial responders (PR; TRG3) and non-responders (NR; TRG0–2) was evaluated by multinomial regression analysis and receiver operating characteristics curves. RESULTS After surgery, 11 patients were CR, 22 PR, and 10 NR. Before CRT, predictions of CR resulted in an ADC value of the 75th percentile and median, with good accuracy (74% and 86%, respectively) and sensitivity (73% and 82%, respectively). During CRT, the best predictor of CR was ΔVT2W (–58.3%) with good accuracy (81%) and excellent sensitivity (91%). After CRT, the best predictors of CR were ΔVT2W (–82.8%) and ΔVb, 1,000 (–86.8%), with 84% accuracy in both cases and 82% and 91% sensitivity, respectively. CONCLUSIONS The median ADC value at pre-treatment MRI and ΔVT2W (from pre-to-during CRT MRI) may have a role in early and accurate prediction of response to treatment. Both ΔVT2W and ΔVb,1,000 (from pre-to-post CRT) can help in the identification of CR after CRT.