Objective:To establish an in vivo model of acute radiation esophagitis in Wistar rats based on a small animal precision radiotherapy platform (SARRP). Methods:Thirty-six Wistar rats were randomly divided into control group, 40, 60 and 75 Gy groups. Based on MRI images, the esophageal target area of rats was outlined and the radiotherapy plan was formulated. The rats were respectively irradiated with 0, 8, 12 and 15 Gy per day for 5 consecutive days. The changes of body weight, food intake, esophageal pathology and magnetic resonance imaging were observed.Results:The body weight of rats in 75 Gy group decreased significantly on the 6th day after irradiation (IR) ( P<0.05). The esophageal tissue of rats in each IR group was thicker than that in control ( F = 14.20, P < 0.05). HE staining showed that the formation rate of radiation-induced esophagitis in 40 Gy and 60 Gy groups were 4/5 and 5/5, respectively, mainly mild. In 75 Gy group, the incidence of radiation-induced esophagitis approached to 5/5, of which 3/5 was severe at 9 d post-IR. The pathological injury scores [ M( Q1, Q3)] of rats in each group were 0, 1.0 (0.5, 2.5), 1.0 (1.0, 2.5) and 4.0 (1.5, 6.0) on the 9th day after IR. There was significant difference between the 75 Gy group and the control group ( H=12.69, P<0.05). After dynamic monitoring of neck MRI images, it was found that the esophageal signal of rats in each IR group increased and widened at 9 d post-irradiation. Conclusions:The animal model of acute radiation-induced esophagitis in rats was successfully established based on a small animal precision radiotherapy platform combined with MRI. 75 Gy was the best irradiation dose and the 9th day was the best observation time point.