Objective:To study the dosimetric differences of hippocampal-avoidance whole brain radiotherapy(HA-WBRT)between non-uniform 9-fields intensity-modulated radiotherapy-flatten filter(9F-IMRT-FF)and 9-fields intensity-modulated radiotherapy-flatten filter-free(9F-IMRT-FFF)mode.Methods:From January to December 2023,the simulated images of computed tomography(CT)location of 20 patients with intracranial metastases who had completed whole-brain radiotherapy at the Department of Radiotherapy of Chengde Central Hospital were selected.The radiotherapy plans of two kinds of modes of brand-new 9F-IMRT-FF and 9F-IMRT-FFF were redesigned in the planning system.The differences of dosimetric parameters of the two kinds of mode plans were compared,as well as the differences of irradiation efficiency of accelerator.Results:The exposure dose(D2%)of 2%volume of target region of planned target volume(PTV)of 9F-IMRT-FFF mode was significantly lower than that of 9F-IMRT-FF mode(t=-2.496,P<0.05).The exposure dose(D100%)of 100%volume of target region,the maximum dose(Dmax)and the mean dose(Dmean)of the left side of hippocampus of 9F-IMRT-FFF mode plan were significantly lower than those of 9F-IMRT-FF mode plan,with statistically significant(Z=-3.179,-3.018,-2.145,P<0.05),respectively.The D100%and Dmax of the right side of hippocampus of 9F-IMRT-FFF mode plan were significantly lower than those of 9F-IMRT-FF mode plan,with statistically significant(Z=-3.099,-3.260,P<0.05),respectively.The monitor unit(MU)value of 9F-IMRT-FFF mode plan increased by 25%than that of 9F-IMRT-FF mode plan,while the treatment time of 9F-IMRT-FFF mode plan shortened 38%than that of 9F-IMRT-FF mode plan,with statistically significant(t=-9.664,-13.312,P<0.05),respectively.Conclusion:Both the non-uniform 9F-IMRT-FF and the 9F-IMRT-FFF can meet the clinically requirement.The 9F-IMRT-FFF has better modulation capabilities in beams,which has more advantages in reducing the dose of radiotherapy for hippocampus,and reducing treatment time,and increasing treatment efficiency.