Role of Diffusion-Weighted Imaging in the Evaluation of Post-Treatment Tumor Response in Rectal Carcinoma

Introduction Rectal cancer has become a major cause of mortality worldwide. Imaging has a primary role in staging and assessing the response to therapy. MRI is superior to all other modalities in local staging of the rectal tumor and in predicting tumor response. Pelvic MRI has an undeniable role in the therapeutic management of rectal cancer, particularly for the determination of the circumferential resection margin (CRM), evaluation of sphincter invasion, and assessment of the extramural vascular invasion. Post-chemoradiotherapy (CRT) staging aims at assessing treatment response and choosing methods for further treatment such as surgical resection or extended CRT. MRI with diffusion restriction is a non-invasive and useful tool for assessing the treatment response of locally advanced lower rectal cancer. It will reduce the burden of extensive abdominoperineal resection (APR) surgery in patients. Objective The purpose of this study was to determine the role of diffusion-weighted imaging (DWI) in the evaluation of post-treatment tumor response in rectal carcinoma. Materials and methods The study was approved by our institutional review board, which waived the requirement for informed consent. The clinical data of all the patients treated for rectal carcinoma at the Shaukat Khanum Memorial Cancer Hospital and Research Centre, Lahore between February 1, 2014, and February 28, 2019, were retrospectively evaluated. The inclusion criteria were as follows: (1) patients with histopathologically proven rectal adenocarcinoma, (2) those who underwent APR before February 2019 at our hospital, and (3) those who underwent MRI including DWI/apparent diffusion coefficient (ADC) imaging before and after CRT. Those patients who had upfront surgery without neoadjuvant CRT and those who did not have MRI imaging with DWI/ADC were excluded from the study. Results A total of 200 patients who fulfilled the inclusion criteria were included in this study. Among those, 141 were males and 59 were females. On histology, 110 had moderately differentiated adenocarcinoma, 25 had well-differentiated adenocarcinoma, and 65 had poorly differentiated adenocarcinomas. Overall diagnostic accuracy of DWI MRI sequence was calculated to be 91%, while the sensitivity was 98.09%, specificity was 65.12%, positive predictive value was 91.12%, and negative predictive value was 90.32%. Conclusion DWI was proven to be very useful in the post-treatment evaluation of tumor response with very high diagnostic accuracy.