Magnetic resonance imaging with Diffusion-Weighted Imaging for post-treatment response assessment in rectal carcinoma: A cross-sectional study at a tertiary care hospital in Karachi.

Abstract

Background: Assessing tumor response after neoadjuvant chemoradiotherapy (CRT) is a crucial step in the management of locally advanced rectal cancer, as it directly influences further treatment planning. Magnetic resonance imaging (MRI), particularly when combined with diffusion-weighted imaging (DWI), has gained an important role by allowing non-invasive evaluation of residual disease.Objective: To evaluate post-treatment tumor response patterns in patients with rectal carcinoma using MRI with diffusion-weighted imaging.Methods: This cross-sectional study conducted at a tertiary care hospital in Karachi, included 168 patients aged 25–85 years with locally advanced rectal cancer (≥T3 stage and/or regional lymph node involvement) who underwent post-CRT MRI with DWI between December 2023 and June 2024. Imaging was performed using a standardized multiparametric rectal MRI protocol, including high-resolution T2-weighted sequences and high b-value DWI (≥800 s/mm²). Tumor response was classified as complete/near complete, good, or poor according to predefined MRI-based criteria. Associations between response patterns and demographic or clinical variables were analyzed.Results: The mean age of the study population was 48.9 ± 15.1 years, with males comprising 59.5% of cases. Complete or near-complete response was observed in 14.3% of patients, good response in 61.3%, and poor response in 24.4%. Overall, 75.6% of patients demonstrated a favorable treatment response.Conclusion: MRI with diffusion-weighted imaging is a reliable and effective modality for assessing post-chemoradiotherapy tumor response in locally advanced rectal cancer. Its use can assist in individualized treatment planning, support organ-preserving approaches, and help avoid unnecessary overtreatment.