Objective: To prospectively monitor perfusion parameters changes in advanced gastric cancer after chemotherapy,and to evaluate whether perfusion CT findings correlate with early response to therapy.Materials and methods: The hospital review board approved this study,and informed consent was obtained from each participant prior to the study.Thirty-six patients with advanced gastric cancer underwent perfusion CT,all of them underwent chemotherapy(3 cycles),followed by surgery,and perfusion CT was repeated after 1 cycle chemotherapy.Blood Flow(BF),Blood Volume(BV),Mean Transit Time(MTT),and Permeability Surface(PS)were computed in the tumor and in normal gastric wall by two independent blinded radiologists.Based on the method for the assessment of pathologic tumor response,all patients divided into two groups: responders and nonresponders.Perfusion parameters before and after therapy were compared by means of the Wilcoxon signed-rank test,differences in proportions of patients were analyzed by the x2 test,P<0.05 was considered statistically significant.Results: 1.BF,BV,and PS were significantly higher in gastric cancer than in normal stomach wall(P<0.001),MTT were significantly lower in gastric cancer than in normal stomach wall(P<0.001)2.BF,BV,and PS in the chemotherapy responders were significantly decreased after chemotherapy(P<0.001),while MTT were significantly increased(P<0.001); BF,BV,and PS in the chemotherapy nonresponders were significantly increased after chemotherapy(P<0.001),and MTT were significantly decreased(P<0.001).3.Perfusion CT parameters changes can indicate response to chemotherapy earlier than changes in tumor volume occurred.4.The baseline BF,BV,and PS of nonresponders were significantly lower(P =0.016,0.023 and 0.018,respectively)than those of responders while the baseline MTT were significantly higher(P=0.022)than those of responders.Conclusions: 1.CT perfusion parameters changes in advanced gastric cancer were able to indicate early response to chemotherapy before changes in tumor volume occurred,and baseline perfusion parameters in advanced gastric cancer can predict pathologic response to chemotherapy.2.CT Perfusion will be a helpful tool in the prediction and early evaluation of pathologic response following chemotherapy in patients with resectable AGC.