Objective To monitor and evaluate the synergistic antitumor effects of programmed death-1(PD-1)checkpoint inhibitor combined with radiation therapy through whole-body dynamic 18 F-Fluorodeoxy glucose positron emission computed tomography(18F-FDG PET/CT)and Patlak multi-parametric analysis.Methods B16F10 mel-anoma dual-tumor mouse model was established and randomly divided into control,PD-1 monoclonal antibody,ra-diation-only,and combination groups(n=6).Whole-body 18F-FDG PET/CT imaging was performed before and 24 hours post-treatment.The changes of maximum standardized uptake value(SUVmax)and metabolic rate of FDG(MRFDG)changes were analyzed and compared.Mice were then euthanized,tumors excised and underwent histo-pathology with HE,CD8,Ki-67 staining to assess immune infiltration and proliferation.Distal tumor volumes were monitored during treatment.Results At 24 hours post-treatment,in the primary tumors,SUVmax and MRFDG values increased compared to pre-treatment in the control group(P＜0.000 1),while they decreased in the combination treatment group(P＜0.000 1),with statistically significant differences.In the distal tumors,SUVmax and MRFDG values increased compared to pre-treatment in the control group,PD-1 monoclonal antibody group,and radiothera-py-alone group.The SUVmax differences were statistically significant in the control group before and after treatment(P＜0.000 1).MRFDG values in the distal tumors showed statistically significant differences in all three groups(P＜0.01 or P＜0.000 1).In the combination treatment group,SUVmax and MRFDG values in the distal tumors de-creased significantly compared to pre-treatment(P＜0.000 1).Post-treatment comparison of SUVmax and MRFDG values in the distal tumors showed that statistically significant differences in SUVmax and MRFDG values were observed among all groups except between the radiotherapy-alone and PD-1 monoclonal antibody groups(all P＜0.05).Im-munohistochemistry results showed that the mean absorbance value of CD8 T lymphocytes in the distal tumor was significantly higher than that in the other three groups(P＜0.001);the mean absorbance value of Ki-67 immuno-histochemistry in the distal tumor proliferation index was significantly lower than that in the other three groups(P＜0.001).Conclusion The synergistic effects of combined treatment reduced distal tumor growth.Whole-body 18F-FDG PET/CT Patlak multi-parametric imaging can monitor the synergistic effects of PD-1 antibody and radiotherapy in B16F10 melanoma,providing reliable imaging parameters for optimizing combinatorial therapies.