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中文摘要：
目的 研究医用直线加速器在静态调强放射治疗（IMRT）照射过程中,内置多叶光栅（MLC）叶片的到位精度及其受机架角度的影响，方法 回顾分析Varian 23EX医用直线加速器在重复10次执行1例鼻咽癌肿瘤静态IMRT过程中产生的动态日志文件,获取各照射野内每条叶片实际走位的相对坐标值,对比放疗计划系统给出的MLC位置坐标,计算Varian 23EX内置Millennium^TM 60对多叶光栅每一条叶片的到位误差和每一对叶片的叶间距误差,对比垂直野（0°）与水平野（103°和257°）不同机架角度对叶片到位精度的影响.结果 全部叶片到位误差分布在±1.00 mm范围内,叶间距误差分布在±0.15 mm范围内，同一射野角度下,每分次治疗间光栅到位误差的标准差值小于0.06 mm.当考虑全部叶片时,103°野的MLC到位误差小于0°野（t=58.74,P＜0.01）,而257°与0°野的MLC到位误差差异无统计学意义;当仅考虑参与移动的叶片时,103°野到位误差仍小于0°野,但257°野到位误差在有限范围（＜0.1 mm）内大于0°野,两组对比,差异有统计学意义（￡=41.95、-4.47,P＜0.01），结论 Varian 23EX内置Millennium^TM 60对MLC在执行静态IMRT治疗过程中的到位精度满足IMRT质量控制要求，分次治疗间,光栅到位重复性好.不同射野角度下,重力因素对光栅到位精度有一定影响,但误差均在质量控制允许范围之内,满足IMRT机械精度要求.动态日志数字化分析的方法有望作为新的质量控制方式改善现有IMRT计划质量控制流程。
英文摘要：
Objective To investigate the impact of gantry angles on the position accuracy of buildin multi-leaf collimator （MLC） during static （step ＆shoot） intensity modulated radiotherapy （IMRT）.Methods The position accuracy of Millennium^TM 60 pairs multi-leaf collimator （MLC） in Varian 23EX medical linear accelerator during 10 fractions of treatments with static intensity modulated radiotherapy （IMRT） was retrospectively analyzed by resolving dynamic therapy log files and MLC planning files.The single leaf position deviation and gap deviation of each MLC pairs were compared between expected values and actual outcomes.The impact of gantry angle on MLC position accuracy was also investigated with paired t-test between vertical and horizontal beams.Results All the MLC position deviations ranged within ±1.0 mm,while the gap deviations were at the range of ± 1.5 mm.The statistical standard deviation of MLC position deviations among fractions was less than 0.06 mm.After all the 60 pairs of MLC leaves were taken into account,the M LC position deviation in the field of 103° was smaller than in the field of 0° （t =58.74,P 〈 0.01）,but there was no significant difference between 257° and 0°,while only the moving leaves were put into consideration,the MLC position deviation in the field of 103° was still smaller than in the field of 0°,but the MLC position deviation in the field of 257° was slightly higher than in thefield of 0° （t =41.95、-4.47,P 〈 0.01）.Conclusions The Millennium^TM 60 pairs MLC in Varian 23EX medical linear accelerator meets the mechanical quality assurance requirement during static IMRT treatments.The MLC positioning showed stable repeatability among treatment fractions.Although the MLC position accuracy is slightly affected by gravity from different gantry angles,but still meets the mechanical QA requirements for medical linear accelerator.This dynamic analysis method is expected to be a novel strategy which may improve the existing QA protocols.
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