Abstract: Objective To investigate the role of apparent diffusion coefficient (ADC) value in the evaluation of therapeutic effect of radiotherapy for pancreatic cancer. Methods Twenty six patients with pancreatic cancer received radiotherapy were examined with magnetic resonance imaging (MRI) before radiotherapy, one month after radiotherapy, three months after radiotherapy, and six months after radiotherapy,and ADC value of diffusion weighted imaging(DWI) was measured. The patients were divided into remission group and non-remission group according to the change rate before and after radiotherapy, SPSS17.0 software was used to analyze the change of apparent diffusion coefficient before and after radiotherapy and the relationship between the change rates of tumor maximum diameter. Results The ADC value of 26 patients with pancreatic cancer increased significantly after radiotherapy (P＜ 0.001); the ADC value of the remission group was significantly lower than that of the non-remission group before radiotherapy (P＜ 0.05); the ADC value of 26 patients before radiotherapy was negatively correlated with the tumor maximum diameter reduction rate (P＜0.01). Conclusions The change of ADC value before and after radiotherapy is of great value to the radiotherapy for pancreatic cancer, especially to the evaluation of the curative effect when the volume of the focus has not changed significantly. It is also of certain value to predict the degree of volume reduction after radiotherapy and to judge the effect of radiotherapy for pancreatic cancer.

Key words: pancreatic cancer, radiotherapy, MRI, apparent diffusion coefficient