关键词: 直肠癌, 新辅助放化疗, 体素内不相干运动扩散加权成像

Abstract: Background and purpose: DWI is an ideal way to check the diffusion of water molecules in vivo. Apparent diffusion coefficient value derived from DWI based on a mono-exponential model does not sufficiently demonstrate the characteristics of tissue behavior. Intravoxel incoherent motion (IVIM) can be used to estimate molecular diffusion and microcirculation in the capillaries separately through bi-exponential fitting of the DWI data using low and high b-value. This study aimed to determine the value of IVIM in predicting treatment response before preoperative chemoradiotherapy in locally advanced rectal cancer. Methods: A cohort of consecutive patients with histologically confirmed rectal adenocarcinoma treated with preoperative chemoradiotherapy followed by total mesorectal excision (TME) surgery was enrolled in a prospective pilot trial. All patients were examined using IVIM at two time points: 2 to 5 days before neoadjuvant chemoradiotherapy, 1 to 4 days before surgery. The perfusion parameters (ADCstandard, D, D^*, f) were measured for tumor. The patients were classified into pathological complete response (pCR) group and non-pCR group according to the pathological results after operation. Those diffusion parameters were compared between before and after neoadjuvant chemoradiotherapy in all patients as well as in pCR and non-pCR groups with the t-test. Results: The final study population consisted of 32 patients. There were 11 patients with pCR and 21 patients with non-pCR. The mean tumor ADCstandard using the mono-exponential model for all patients was (133.2±21.5)×10^-5 mm/s before neoadjuvant chemoradiotherapy, (166.9±29.7)×10^-5 mm/ s after neoadjuvant chemoradiotherapy. The parameters showed significant difference between those two groups. By using the bi-exponential DWI in this study, we found that the mean tumor D^* was (4 471±1 271)×10^-5 mm/s for pCR group, (5 749±1 722)×10^-5 mm/s for non-pCR group before neoadjuvant chemoradiotherapy. After neoadjuvant chemoradiotherapy, the mean tumor D was (97.0±14.6)×10^-5 mm/s for pCR group, (113.4±22.6)×10^-5 mm/ s for nonpCR group. All the parameters showed significant differences between those two groups (all P<0.05). Conclusion: In locally advanced rectal cancer, IVIM of bi-exponential DWI can aid in describing diffusion information of tumor.

Key words: Rectal cancer, Neoadjuvant chemoradiotherapy, Intravoxel incoherent motion