Objective To compare the dose distribution between volumetric-modulated arc therapy ( VMAT ) and intensity-modulated radiotherapy ( IMRT ) in patients with brain metastases receiving hippocampus-sparing whole brain radiotherapy. Methods Forty-six patients with brain metastases admitted to our hospital from 2013 to 2016 were recruited in this study. After fusing the CT and MRI images, the hippocampus was delineated on the fusion images. The three-grade hippocampal avoidance regions were created by using a volumetric expansion of 3,5 and 10 mm surrounding the hippocampus. The planning target volume ( PTV) was calculated by subtracting the 5-mm expansion surrounding the hippocampus from the whole brain. The prescription dose was 30 Gy/10 fractions. The 7-field IMRT and single arc VMAT were designed for each case. The dose distribution of PTV,hippocampus and other organs at risk ( OARs) were evaluated in both plans. Results The PTV was statistically compared between VMAT and IMRT:V95:95. 90％ and 94. 97％( P=0. 000 );V90:98. 17％ and 97. 48％( P=0. 000 );CI:0. 825 and 0. 813 ( P=0. 013);HI:0. 277 and 0. 289(P=0. 025).The hippocampal dose was also compared between VMAT and IMRT:the Dmax of hippocampus was 1698. 9 cGy for VMAT and 1784. 9 cGy for IMRT (P=0. 002).TheDmean of hippocampus was 1183. 8 cGy for VMAT and 1112. 7 cGy for IMRT (P=0. 000).No statistical significance was observed between IMRT and VMAT in protecting the OARs except the chiasma opticum ( 3262. 6 cGy and 3529. 3 cGy,P=0. 000).The MU and treatment time of VMAT and IMRT were 651 and 2768( P=0. 000) ,and 188 s and 504 s ( P=0. 000) . Conclusions The dose distribution of PTV in VMAT is significantly better than that in IMRT. VMAT is advantageous in protecting the hippocampus than IMRT. VMAT can significantly shorten treatment time and MU and enhance the equipment utilization. Besides, VMAT can achieve the goal of protecting the hippocampus and meet the prescription dose requirement of PTV.

Objective To explore the relationship between anxiety sensitivity and psychological stress before parachuting training among parachuting trainees and the mediating role of resilience between them.Methods Anxiety sensitivity index scale(version 3),resilience scale,psychological stress self-evaluation test and self-compiled general information questionnaire were employed for 258 parachuting trainees before training.Pearson correlation analysis was used to analyze the correlations among anxiety sensitivity,resilience and psychological stress.A multiple linear regression analysis was conducted with anxiety sensitivity and resilience as independent variables and psychological stress as dependent variable to explore the relationships among these 3 factors.The mediating effect of resilience on the relationship between anxiety sensitivity and psychological stress was examined using the Hayes Process macro program and bias corrected non-parametric percentile Bootstrap method.Results Before parachuting training,the prevalence of psychological stress among parachuting trainees was 5.0%(13/258).The correlations between anxiety sensitivity,resilience and psychological stress were significant(all P＜0.01).Anxiety sensitivity was positively associated with psychological stress among parachuting trainees(b=0.412,t=7.062,P＜0.01),while resilience was negatively associated with psychological stress(b=-0.187,t=-3.722,P＜0.01).Anxiety sensitivity and resilience were found to explain 31.4%of the total variance.Resilience partially mediated the effect of anxiety sensitivity on psychological stress,accounting for 20.48%of the total effect.Conclusion Parachuting trainees are at a relatively low stress level,with good psychological adaptation.Resilience plays a partial mediating role in the association between anxiety sensitivity and psychological stress.More attention should be paid to parachuting trainees with high anxiety sensitivity,enhancing their resilience,and reducing psychological stress before parachuting training.