This study aimed to establish a predictive model for neoadjuvant chemoradiotherapy (nCRT) response in patients with locally advanced rectal carcinoma (LARC) using clinicopathological (CP) features along with radiomics from pretreatment Magnetic Resonance Imaging (MRI) 3D T2W contrast sequence scans. The study also assessed the impact of radiomic dimensionality on predictive performance. Seventy-five patients were prospectively enrolled with clinicopathologically confirmed LARC who underwent nCRT before surgery. Tumor properties were assessed by calculating 2142 shape, first-order, and second-order radiomics features. Least absolute shrinkage and selection operator (LASSO) and multivariate regression were used for feature selection. Two predictive models were constructed, one using 72 CP and 107 radiomics features, and the other using 72 CP and 1862 radiomics features. The models revealed moderately advantageous impact of increased dimensionality, while their predictive performance was in the range generally considered excellent, with respective AUCs of 0.86 and 0.90. A CP-only model (AUC=0.80) served as the benchmark for predictive performance without radiomics. The predictive models developed in this study using pretreatment MRI data, radiomics features, and clinicopathological parameters could potentially be used to routinely predict chemoradiotherapy responders, enabling clinicians to personalize treatment strategies for rectal carcinoma.