Quantitative Assessment of Rectal Cancer Response to Neoadjuvant Combined Chemotherapy and Radiation Therapy: Comparison of Three Methods of Positioning Region of Interest for ADC Measurements at Diffusion-weighted MR Imaging.

Purpose To determine the impact of three different methods of region of interest (ROI) positioning for apparent diffusion coefficient (ADC) measurements on the assessment of complete response (CR) to neoadjuvant combined chemotherapy and radiation therapy (CRT) in patients with rectal cancer. Materials and Methods Institutional review board approval was obtained for this study; all patients gave written informed consent. ADCs were measured by two radiologists using three circular ROIs (three-ROIs), single-section (SS), and whole-tumor volume (WTV) methods in 62 patients with locally advanced rectal cancer on pre- and post-CRT images.