Background: Following neoadjuvant chemoradiation, 25% 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, 19 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 (% ∆ADC) 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 52.9 (29-73) years. There were no significant associations between pre and postoperative ADC values and pCR. However, % ∆ADC had a significant relationship with complete response to treatment. Based on the ROC chart, the value of 15% was selected as cut-off with 56% specificity and 67% sensitivity. The positive and negative predicting values were 77.8% and 40%, respectively.
Conclusion: The mean %∆ADC increase seems to be a valid tool to differentiate complete responders from non-responders after CRT in locally advanced rectal cancer.