Rectal Cancer: Assessing Response to Neoadjuvant Therapy.

MR imaging plays a crucial role in the post-CRT assessment of rectal cancer; results are used for treatment planning. Radiologists should assess response or progression, possibility of a complete response, risk factors for incomplete resection, and nodal stage. T2-weighted MR imaging with diffusion-weighted imaging yields the best results to identify a complete response, but endoscopy is also very important. Overstaging of transmural and MRF invasion after CRT occur regularly, owing to residual stranding regarded as tumor to err on the safe side. Nodal restaging is a challenge. A structured report format or checklist is recommended.