模拟呼吸运动对肿瘤三维技术放疗的剂量分布影响

摘要

目的 通过模拟呼吸运动研究呼吸运动对三维技术放疗剂量分布的影响.方法 对11例肺癌患者进行三维技术放疗计划设计,将二维半导体阵列Mapcheck放在呼吸模拟运动平板3cm等效水模上,使用近似呼吸运动周期为3.5s,运动幅度分别为±3、±5、±10、±15 mm,比较运动和静止状态下Mapcheck实测的剂量分布和治疗计划系统输出的相应平面剂量分布.两组数据行配对t检验.结果 呼吸运动均能降低靶区剂量分布的适形度,剂量分布产生模糊效应;11例患者呼吸运动状态下,3DCRT-QA的γ通过率平均值(3％/3 mm)均大于动态IMRT-QA的,且相互比较的P均＜0.05;通过Mapcheck系统分析出呼吸运动对3DCRT剂量分布的影响主要集中在靶区周边,可对动态IMRT的影响分布于整个靶区.结论 对呼吸运动幅度较大的肿瘤建议采用3DCRT技术,更能确保运动的肿瘤得到预期较准确的剂量分布,若采用IMRT技术应根据情况对运动肿瘤进行呼吸运动补偿等方法以确保肿瘤相对静止.%Objective To evaluate the effects of respiratory on dose distributions in three dimensional conformal radiotherapy (3 DCRT) and intensity-modulated radiotherapy (IMRT).Methods The dose distributions were measured with a Sun Nuclear Mapcheck 2D-ARRAY placed on a moving platform home-made to simulate the respiratory.The periodic motion of the moving platform was 3.5 s.The rang of the moving platform was ± 3 mm,±5 mm,± 10 mm,± 15 mm.Dosimetric comparisions for 3DCRT and IMRT plans were performed by means of Gamma analysis with 3％ and 3 mm,respectively.Dates of two groups were used by paired t-test.Results The respiratory could reduce the target dose and conformal index,blurring effect of dose distribution.The pass rate (3％/3 mm) in 3DCRT was greater than it in IMRT of the 11 cases,and P ＜ 0.05 ; The failed points were mainly near the field edge for 3 DCRT plans,but located in the whole target volumes for IMRT plans.Conclusions Respiratory motion blurred the dose distribution of 3DCRT and IMRT,yet the influence on IMRT was much more striking.As for tumors with large motion amplitude,it is advisable to use 3DCRT rather than IMRT techniques.3DCRT may deliver a more reliable dose distribution by cautiously delineating the PTV margin.