Use of shear wave elastography in the evaluation of local advanced rectal cancer after neoadjuvant radiochemotherapy: the initial experience

Objective To investigate the value of shear wave elastography(SWE) to evaluate local advanced rectal cancer after neoadjuvant radiochemotherapy. Methods In a retrospective study, endorectal ultrasound(ERUS) and endorectal SWE were performed in 73 patients with local advanced rectal cancer before and after neoadjuvant radiochemotherapy. The mean and maximum values of Young′s modulus for SWE to evaluate the lesions before and after neoadjuvant radiochemotherapy were recorded. According to the postoperative pathological T stage, the lesions were divided into reduction of T stage group and non-reduction of T stage group. The efficacy of ERUS in diagnosing reduction of T stage was calculated, and the differences of the mean and maximum values of Young′s modulus between reduction of T stage group and non-reduction of T stage group was calculated, and the differences between the two groups were compared. ROC curves were constructed by the difference of mean and maximum Young′s modulus of lesions before and after neoadjuvant radiochemotherapy, respectively, to evaluate the diagnostic value of the difference in predicting reduction of T stage. Results A total of 57 cases had reduction of T stage after neoadjuvant radiochemotherapy (57/73, 78.1%). The mean and maximum values of Young′s modulus before and after neoadjuvant radiochemotherapy were compared, and the differences were statistically significant(all P<0.01). After neoadjuvant radiochemotherapy, the values of Young′s modulus of the lesions increased with the increase of pT stage. Compared with the mean values of Young′s modulus of the lesions in pT3 stage, the differences of the mean values of Young′s modulus of the lesions in pT0, pT1 and pT2 stages were statistically significant(all P<0.01). Compared with the maximum values of Young′s modulus of the lesions in pT3 stage, the differences of the maximum values of Young′s modulus of the lesions in pT0 and pT1 stage were statistically significant(all P<0.01). The differences of the mean value and the maximum value of Young′s modulus in the reduction of T stage group and the non-reduction of T stage group was statistically significant(all P<0.01). The ROC curve was established and determined by calculation. Taking the average difference of 34.7 kPa as the best diagnostic threshold, the average hardness of the lesion after neoadjuvant radiochemotherapy decreased more than 34.7 kPa to diagnose the reduction of T stage, the sensitivity, specificity and accuracy were 87.7%, 93.8% and 89.0%, respectively. Compared with ERUS, the difference was statistically significant(P=0.032). Conclusions Shear wave elastography is an effective technology to help ERUS in evaluating the lesions of rectal cancer after neoadjuvant radiochemotherapy and has a promising future. Key words: Endosonography; Rectal neoplasms; Elasticity imaging techniques; Shear wave elastography; Neoadjuvant radiochemotherapy