全脑放疗中海马保护的关键问题研究

Key issues of hippocampus protection in whole brain radiotherapy

目的探讨全脑放疗(WBRT)中海马保护的关键问题。方法通过文献检索、资料汇总来明确海马勾画方法;汇总不同条件下达到认知功能保护的海马剂量限值;分别采用共面调强放疗(IMRT)、容积旋转调强放疗(VMAT)和螺旋断层放疗(HT)技术对5例WBRT行海马保护的肺癌脑转移患者进行放疗计划设计,并比较3种放疗计划对应的海马、靶区及正常组织的剂量学参数。结果海马的勾画基于MRI-CT图像与参考RTOG 0933报告进行,建议分段勾画海马的头部、体部及尾部;达到认知功能保护的海马剂量限值推荐为Dmax<17Gy、Dmean<10Gy、D40%<7.5Gy。在IMRT、VMAT和HT计划中,海马体Dmax、Dmean分别为(22.64±0.33)、(23.81±0.42)、(8.02±0.75)Gy和(20.32±0.22)、(21.37±0.63)、(6.83±0.96)Gy,HT计划<IMRT计划<VAMT计划(均P<0.05);均匀性指数(HI)的平均值分别为0.22±0.04、0.31±0.02和0.21±0.02,HI、IMRT计划均低于VMAT计划(均P<0.05);PTV的V90、V95的平均值分别为(98.59±0.28)%、(98.95±0.19)%、(98.72±0.24)%和(97.72±0.24)%、(97.75±0.20)%、(97.56±0.35)%,3种放疗计划比较差异无统计学意义(P>0.05)。结论准确勾画海马、合理确定海马保护区及采用HT计划是WBRT中海马保护的关键,能保证良好靶区剂量覆盖及靶区剂量均匀性,并使海马受照剂量更低。

Objective To explore the key issues and solutions of hippocampus protection in whole brain radiotherapy(WBRT).Methods The method of hippocampal delineation was clarified by literature retrieval and data summary.The hippocampus limited dose for protecting cognitive function in different conditions were summarized.The radiotherapy plans were designed for 5 cases with hippocampus protection in WBRT by IMRT VMAT and HT,and the dosimetric parameters of the hippocampus,target area and normal tissues corresponding to the three radiotherapy plans were compared.Results The delineation of hippocampus should be based on MRI-CT images and referred to the RTOG 0933 report,and it was recommended to trace the head,body and tail of the hippocampus in sections.The limited dose of hippocampus for the cognitive function protection was recommended as Dmax<17Gy,Dmean<10Gy and D40%<7.5Gy.The hippocampus Dmax and Dmean in the plan of IMRT VMAT and HT were(22.64±0.33)Gy,(23.81±0.42)Gy,(8.02±0.75)Gy and(20.32±0.22)Gy,(21.37±0.63)Gy,(6.83±0.96)Gy,and statistics indicated that the HT<IMRT<VAMT(P<0.05).The mean value of HI were 0.22±0.04,0.31±0.02 and 0.21±0.02,and the value of HT and IMRT were less than VMAT(P<0.05).The PTV mean value of V90 and V95 in the three plans were(98.59±0.28)%,(98.95±0.19)%,(98.72±0.24)%and(97.72±0.24)%,(97.75±0.20)%,(97.56±0.35)%,there was no significant difference among the three plans(P>0.05).Conclusion It is important to delineate the hippocampus accurately and determine the hippocampal reserve area reasonably.At the same time,adopting the HT plan can ensure the PTV with good dose coverage and dose uniformity,and the hippocampal dose can be much lower.