Abstract: Objective To evaluate the application value of whole abdominal plain CT in the assessment of the efficacy of targeted therapy for gastrointestinal stromal tumors (GIST). 
Methods Fifty-three patients with pathologically confirmed GIST who received targeted therapy and had complete pre-and post-treatment imaging were retrospectively analyzed in the Fourth Hospital of Hebei Medical University from Mar. 2015 to Sept. 2022. The target lesions were selected with reference to the solid tumor efficacy evaluation criteria Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. The length diameters and CT attenuation values of the target lesions before and after treatment were measured on the plain and venous images, respectively, and the rate of change in the sum of the length diameter and that in the mean CT value were calculated. Observations were made to determine the presence of new lesions, new hemorrhages in target lesions, and calcifications. Efficacies were evaluated according to both the RECIST1.1 and Choi criteria. The results of the efficacy assessment of the scanning and venous phases were compared. Radiation doses were recorded of each examination for both plain and enhanced CT scans. 
Results The differences between the sum of the length diameters of the target lesions and the change rate of the sum of the length diameters measured in the plain and venous phases were not statistically significant (both P＞0.05) and were in good agreement ［intraclass correlation coefficient （ICC） values of 1.000 and 0.999, respectively］. The difference in the change rate of the mean CT values of the target lesions measured by both was statistically significant (P＜0.05), but the consistency was strong (ICC value of 0.672). Three new lesions, three intratumoral hemorrhages, and five intratumoral calcifications appeared after treatment, all of which could be identified by plain scanning. With reference to the RECIST1.1 criteria and Choi criteria, the consistency in the assessment results of the efficacy of the plain and venous phases was very strong, with Kappa values of 1.000 (P＜0.05) and 0.882 (P＜0.05), respectively. Radiation dose reduced approximately 70.11% for plain scan compared with enhanced scan. 
Conclusion The whole abdominal plain CT scan reduces the radiation exposure and examination expenses of patients and can evaluate the targeted therapeutic effect of gastrointestinal stromal tumors relatively accurately, which has certain clinical application value. 

Key words: gastrointestinal stromal tumors, multi-detector computed tomography, targeted therapy