Ali Yaghobi Joybari - Department of Radiation Oncology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Fariba Jozian - Department of Radiation Oncology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Sam Alahyari - Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Saeed Nasiri - Department of Radiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Majid Samsami - Department of General Surgery, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Saleh Sandoughdaran - Department of Clinical Oncology, St. Luke’s Cancer Centre, Royal Surrey County Hospital, Guildford, UK

Background: Following neoadjuvant chemoradiation, ۲۵% of patients with rectal cancer experience pathologic complete response (pCR). With the appropriate imaging method for this group of patients, it would be possible to use less invasive methods. The aim of this study was to assess the ability of diffusion-weighted magnetic resonance imaging to predict pCR after neoadjuvant chemoradiation in patients with rectal cancer.Method: In this prospective study, ۱۹ patients with rectal cancer were examined. Magnetic resonance imaging of patients with diffusion-weighted imaging was performed in two stages: one week before the start of chemoradiotherapy (CRT) and seven weeks after the end of CRT to evaluate the results of treatment. Apparent diffusion coefficient (ADC) was measured before and after treatment. The percentage of ADC (% ΔADC) increment was also calculated. The patients were divided into three groups according to the surgical report: complete responders, partial responders, and non-responders. Optimal cut-off point was determined via ROC diagram.Results: The mean age of the patients was ۵۲.۹ (۲۹-۷۳) years. There were no significant associations between pre and postoperative ADC values and pCR. However, % ΔADC had a significant relationship with complete response to treatment. Based on the ROC chart, the value of ۱۵% was selected as cut-off with ۵۶% specificity and ۶۷% sensitivity. The positive and negative predicting values were ۷۷.۸% and ۴۰%, respectively. Conclusion: The mean %ΔADC increase seems to be a valid tool to differentiate complete responders from non-responders after CRT in locally advanced rectal cancer.

Rectum neoplasms, Chemoradiotherapy, Apparent diffusion coefficient, Diffusion magnetic resonance imaging, Neoadjuvant treatment