Objective To evaluate the dose distribution of hippocampal sparing whole-brain proton therapy based on the treatment planning system of Mevion S250i proton therapy system.Methods Twenty patients undergoing hippocampal sparing whole-brain radiotherapy were selected.Under the same optimal conditions,plans using VMAT,fixed-angle IMPT without a-daptive aperture,IMPT with static adaptive aperture and IMPT with dynamic adaptive aperture were designed for each pa-tient.HI,CI,GI and the dose of hippocampus,lens,optic nerve,cochlea in different groups were compared.Results Compared with the VMAT plans,the IMPT plans without the adaptive aperture improved the target homogeneity index from(0.45±0.15)to(0.60±0.08),and the high-dose D2 in the targets decreased from(3368.22±65.94)cGy to(3270.67±104.78)cGy,and the irradiation doses of the hippocampus,lens and cochlea were significantly reduced(P＜0.05).The target gradient of IM-PT plans could be improved using static adaptive aperture,and the dose of lens could be further reduced(P＜0.05).The target gradient and conformal degree of the IMPT plans were significantly improved using dynamic adaptive aperture,and the dose of the optic nerves,lens and cochleae were further reduced(P＜0.05).Conclusion IMPT has a dosimetric advantage over VMAT in hippocampal sparing whole-brain radiotherapy.The use of Mevion adaptive aperture can not only further optimize the dose to the target area,but also minimize the radiation doses to the normal tissue around the target area,which has a good clinical appli-cation prospect.
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