This paper introduces a new intensity-compensated longitudinal non-rigid registration method for Contrast Enhanced Mammography monitoring neoadjuvant chemotherapy (NAC). The registered NAC image subtraction, called residual fields, allows to discriminate between different lesion responses to treatment using features extraction. The approach registers low-energy 2D images of the exams acquired before and after the chemotherapy. The measured motion is then applied to the corresponding dual-energy recombined images. Consequently, the difference in registered images allows identifying local density and iodine uptake changes, especially in the lesion area. The registration converged for all 51 patients with 208 image pairs. Finally, the residual fields can be used to extract clinically relevant features used to assess the response of the treatment. The lesion response classification model, evaluated with the AUC and F-score, performed better when taking into account the residual features (AUC: 0.92 vs 0.79).