To investigate the clinical value of apparent diffusion coefficient (ADC) measurements in different diffusion weighted imaging (DWI) regions of interest (ROIs) in the evaluation of the therapeutic efficacy for rectal cancer.

A total of 58 patients diagnosed with rectal cancer by histopathological examination and underwent neoadjuvant chemoradiotherapy (NCRT) were included in the study. Routine MRI sequence and DWI sequence were performed before and after treatment, where the b-value of DWI sequence was 1000. The ADC values were measured by the multiple small samples method, maximum slice method, and overall volume method, respectively. According to the postoperative pathology, the patients were divided into either a complete response (pCR) group or a non-complete response (non-CR) group. The differences of ADC values among different groups with different measurement methods were compared, and ROC curve analysis was performed to analyze the value of different ADC measurements in evaluating NCRT efficacy for rectal cancer.

ADC values measured by the multiple small samples method before treatment were lower than those measured by the maximum layer method and global volume method, and there were statistical differences in ADC values between the three methods (P<0.05). After treatment, ADC values measured by multi-sample method were significantly higher than those measured by the maximum slice method and global volume method (P<0.05). ADC values measured by all the three ROI methods after treatment were significantly higher than those before treatment (P<0.05). ADC values measured by the three ROI methods did not differ significantly in the pCR group, non-pCR group, TRG remission group, and TRG non-remission group (P>0.05). ADC values measured by the three ROI methods were significantly higher in the pCR group than in the non-pCR group, and in the TRG remission group than in the TRG non-remission group (P<0.05 for all). Spearman correlation analysis showed that ADC values measured by the overall volume method had the best negative correlation with the therapeutic efficacy for NCRT assessed by both pCR and TRG criteria (r=-0.557 and-0.564, P<0.05). The ADC values measured by the multiple small samples method and maximum slice method were also negatively correlated with the therapeutic efficacy for NCRT assessed by both pCR and TRG criteria (P<0.05). According to the pCR evaluation criteria, the areas under the curves (AUCs) of the ADC values measured by the overall volume method, the maximum slice method, and the multiple small samples method were 0.816, 0.781, and 0.721, the sensitivities were 89.67%, 85.82%, and 76.29%, and the specificities were 82.60%, 79.58%, and 84.33%, respectively. According to the TRG evaluation criteria, the AUCs were 0.804, 0.767, and 0.719, the sensitivities were 87.12%, 84.30%, and 74.24%, and specificities were 81.17%, 76.53%, and 81.19%, respectively.

The ADC values measured by different ROI delineation methods can evaluate the efficacy of NCRT for rectal cancer, and the ADC values measured by the overall volume method were superior in terms of sensitivity and specificity.