中文摘要：

目的探讨调强放疗中分次间摆位误差对脊髓物理剂量和生物效应剂量的影响。方法在治疗计划系统上模拟实际的摆位过程和无摆位误差的原计划进行比较，确定1个疗程中脊髓累积受照的物理剂量和生物效应剂量与相应计划值的差别。模拟在8例鼻咽癌患者的治疗计划上进行。每个病例有5种摆位情况：S0为原计划之摆位无摆位误差；S1、S2、S3和S4为模拟摆位，S1、S2和S3有同样的系统摆位误差，S1无随机摆位误差，S2的随机摆位误差小于S3；S2、S3的摆位误差呈正态分布；S4无随机摆位误差，系统摆位误差大于S1、S2和S3。结果与S0相比，S1、S2、S3和S4的脊髓参考点疗程累积剂量分别增加6．9%±1．3%、7．0%±1．4%、7．8%±1．5%和11．6%±1．0%；其总生物效应剂量分别增加9．2%±1．8%、9．7%±1．9%、11．2%±2．2%和15．7%％±1．4%；S2、S3分次剂量有波动，分次剂量标准偏差分别为11．4%±2．6%、16．6%±2．8%。结论较小的摆位误差也会造成脊髓剂量较大的改变；系统摆位误差主要影响疗程总量，而随机摆位误差主要产生分次间剂量波动；同样改变见于生物效应剂量且稍大于物理剂量。

英文摘要：

Objective To investigate the physical dose and biologically effective dose uncertainty in the spinal cord from inter-fraction setup errors in intensity-modulated radiation therapy. Methods Simulated actual setups on treatment plan system, compared with primary plan without setup errors to evaluate the difference in the physical dose and biologically effective dose between plan and delivery was carried out. Eight patients in the test, everyone had 5 setups, S0-S4. S0 was the setup of primary plan without setup errors. S1, S2, S3 and S4 were actual clinical setups simulated. S1, S2 and S3 had the same system setup errors, S1 showed no random setup errors, and the random setup error of S2 was smaller than S3. The setup errors of S2 and S3 were normally distributed. There was no random setup in S4 and its system setup errors were greater than those of S1, S2 and S3. Results Compared with S0, the total dose of the reference point in the cord in S1, S2, S3 and S4 were addod 6.9%±1.3%, 7.0%±1.4%, 7.8%±1.5% and 11.6%±1.0%, respectively; the total biologically effective dose of the reference point of cord in S1, S2, S3 and S4 were added 9.2%±1.8%, 9.7%±1.9%,11.2%±2.2% and 15.7%±1.4%, respectively; the standard deviation of fraction dose in S2 and S3 were 11.4%±2.6% and 16.6%±2. 8%, respectively. Conclusions Tiny setup errors could give rise to a big change of the dose in the spinal cord, with the change of total dose determined by system errors, the random errors would lead to dose fluctuation. As found in the biologically effective dose, the change were little more than the physical dose.