Predictive Value of Transrectal Ultrasound and Contrast‐Enhanced Ultrasound Quantitative Parameters for Pathological Complete Response to Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer

PURPOSE: To investigate the predictive value of transrectal ultrasound (TRUS) and contrast-enhanced ultrasound (CEUS) quantitative parameters before and after neoadjuvant chemoradiotherapy (NCRT) for pathological complete response (pCR) in locally advanced rectal cancer (LARC). METHODS: Seventy LARC patients who underwent surgery after NCRT were retrospectively analyzed. Quantitative parameters of TRUS and CEUS before and after NCRT were recorded, and their rates of change were calculated. Patients were classified into pCR and non-pCR (npCR) groups based on pathological tumor regression grading (pTRG). Differences in parameters before and after NCRT were compared between groups, and correlations between parameters and pTRG were analyzed. Receiver operating characteristic curves were used to assess predictive efficacy. RESULTS: Tumor thickness, peak intensity (PI), and slope (S) were significantly reduced after NCRT in the pCR group (p < 0.01). Tumor thickness, PI, and S after NCRT were positively correlated with pTRG (r = 0.402, 0.614, and 0.576, all p < 0.01), while their rates of change were negatively correlated with pTRG (r = -0.315, -0.498, and -0.440, all p < 0.01). Thickness change rate (OR = 1.035, p = 0.031), PI change rate (OR = 1.057, p = 0.018) were independent predictors of pCR. The optimal cut-off values for predicting pCR after NCRT were as follows: thickness change rate 39.4% (AUC = 0.733), PI change rate 60.8% (AUC = 0.856). CONCLUSION: The change rates of tumor thickness and CEUS quantitative parameter (PI) after NCRT may serve as effective predictors of pCR in LARC patients.