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Diffusion-weighted imaging for evaluating lymph node eradication after neoadjuvant chemoradiation therapy in locally advanced rectal cancer

Background As lymph node (LN) eradication is the prerequisite for clinical surveillance or local excision for patients who have achieved a complete response after preoperative chemoradiation therapy (CRT), the radiological evaluation of LN eradication is important. Purpose To evaluate the added value of diffusion-weighted imaging (DWI) in the evaluation of LN eradication after CRT in patients with locally advanced rectal cancer (LARC). Material and Methods Ninety-five consecutive patients (64 men, 31 women; mean age, 59 years; range, 32–82 years) who underwent pre- and post-CRT 1.5-T MRI with DWI (b = 0, 1000 s/mm2) were enrolled. To evaluate the added value of DWI in the evaluation of LN eradication after CRT, two radiologists first independently read the pre- and post-CRT T2-weighted (T2W) images and then read the combined T2W imaging set and the pre- and post-CRT DWIs with a 4-week interval. The radiologists recorded their confidence scores for LN eradication using a 5-point scale on a per-patient basis. The diagnostic performances were compared between the two reading sessions for each reader with pair-wise comparisons of receiver-operating characteristic curves. Histopathological reports served as the reference standards for LN eradication. Results The study population consisted of an LN-eradicated group (n = 66) and a non-eradicated group (n = 29). The diagnostic performances did not significantly differ between the two reading sessions for the two readers (AUCs for reader 1, 0.770 and 0.774, P = 0.8155; for reader 2, 0.794 and 0.798, P = 0.8588). Conclusion Adding DWI to T2W imaging provided no additional diagnostic benefit for the evaluation of LN eradication following CRT in patients with LARC.