Purpose The purpose of this paper is to compare the dosimetric characteristics of protection of hippocampus between VARIAN RapidArc(volumetric modulated arc therapy,VMAT)and fixed-field dynamic intensity-modulated radiation therapy(IMRT)for patients with brain metastases from lung cancer in the whole brain irradiation.Methods For patients with brain metastases from lung cancer in 6 cases,two kinds of radiotherapy treatment plans,IMRT and RapidArc double-arc VMAT,were designed respectively.On the premise that the clinical requirements were satisfied,the comparisons of target dose distribution,conformity,homogeneity index,dose to OARs,number of monitor units and treatment time between IMRT and RapidArc were explored for their dosimetric difference.Results The two kinds of treatment plans both can meet the requirements of clinical treatment.The target conformity and homogeneity of RapidArc were better than IMRT.Except for the maximum dose(Dmax)to lens,there was no significant difference(P > 0.05)in other results between two kinds of plans.Generally,the irradiation dose to OARs in RapidArc plan is superior to that in IMRT(P < 0.05); Compared with IMRT,RapidArc reduced an average number of monitor units by 67%.The average delivery time of IMRT was 573s and that of RapidArc was 150s.It is obvious that the patients treatment time was shortened by RapidArc.Conclusion The target dose distribution of RapidArc is better than IMRT.RapidArc can reduce the dose to OARs significantly while reducing the number of monitor units and treatment time obviously.