多叶准直器叶片速度对滑窗调强放疗剂量分布的影响研究

The Effect of Speed of Multileaf Collimator on Dose Distribution With Sliding Windows Intensity-Modulated Radiotherapy

目的:研究多叶准直器(MLC)叶片运行速度对采用滑窗技术实施动态调强放射治疗时剂量分布的影响。方法:手工设计一组滑窗调强(SW-IMRT)照射野叶片序列(子野)文件P-MLC,在不同的剂量率、不同的机器跳数(MU)条件下运行,使得叶片的运行速度分别为1.0 cm/s、2.0 cm/s、3.0 cm/s、4.0 cm/s、5.0 cm/s、6.0 cm/s、7.0 cm/s、8.0 cm/s、10.0 cm/s、15.0 cm/s,用Mapcheck测量不同速度运行时的剂量分布,分别与PMLC在计划系统里计算的剂量分布相比较;选择10例鼻咽癌调强计划,在加速器上分别以100 MU/m、200 MU/m、300 MU/m、400 MU/m、500 MU/m、600 MU/m剂量率运行,用Mapcheck测量其剂量分布并与计划系统剂量分布比较其通过率;同时记录10例病人不同剂量率条件下运行时的加速器日志文件,将日志文件转换成实际运行MLC文件D-MLC后,将D-MLC导入计划系统重新计算,模拟比较不同剂量率条件下病人体内的剂量分布的差别。结果:在MLC计划速度设置为15.00 cm/s时,加速器实际叶片速度达到了(2.78±1.45)cm/s,最大速度为4.55 cm/s;加速器在MLC设定速度不超过5.00 cm/s运行计划文件时,通过降低剂量率的方式可以匹配叶片运动速度的限制,保证了实际照射时加速器输出的射野通量与计划设计时的最佳射野通量相一致,Mapcheck验证通过率在99%以上,但在设定速度超过5.00 cm/s运行计划文件时,通过降低剂量率的方式已无法匹配叶片运动速度的限制,Mapcheck验证通过率在随着设定速度的上升而降低;对实际临床病例的研究并未出现上述结果,不同的剂量率运行时其剂量分布及Mapcheck验证通过率没有明显差异(P=0.999)。结论:MLC叶片的运动速度可能会对滑窗调强放疗技术的剂量分布产生一定的影响,尽管在临床实际治疗中,这种影响很微弱,但这种方法可以作为直线加速器和治疗计划系统的验收或实施SW-IMRT技术日常QA工作的一种手段。

Objective： To explore the effect of speed of multileaf collimator（MLC） on the dose distribution of the dynamic intensity-modulated radiation therapy.Methods： A group of MLC files was designed with sliding window intensity-modulated （SW-IMRT） radiation fields and was run with different dose rate and different machine unit（MU）,so that the speed of the leaf were modulated at 1.0 cm/s,2.0 cm/s,3.0 cm/s,4.0 cm/s,5.0 cm/s,6.0 cm/s,7.0 cm/s,8.0 cm/s,10.0 cm/s respectively.The dose distribution with Mapcheck was measured,and the dose distribution which calculated in planning system was compared. Ten cases of nasopharyngeal carcinoma intensity-modulated plan,with 100 MU/m 200 MU/m,300 MU/m,400 MU/m,500 MU/m,600 MU/m dose rate separatively on the accelerator and dose distribution was measured with Mapcheck,and compared the dose distribution planning system in passing;simultaneously recording ten patients under the condition of different dose rate run-time accelerator log files,will log file conversion into actual operation after DMLC MLC documents,will DMLC import plan system recalculate,comparing different dose rate in patients die under the condition of the dose distribution and primitive dose distribution difference.Results： The accelerator actual blade movement speed reached（2.78±1.45） cm/s,maximum speed 4.55 cm/s;for in not more than 5.00 set speed cm/s,accelerator in operation plan file,the way by lowering the dose rate can match the vane motion speed limit,to ensure the actual illuminate the accelerator output when shooting wild flux and plan the best shot when designing Mapcheck wild flux consistent and verified in above 99%,but pass in setting cm/s faster than 5.00 when planning document,the accelerator in operation by lowering the dose rate,already can＇t match the way blade movement speed limits,Mapcheck verification with the speed of the passing rate rise and set down;on the actual clinical case research does not appear afore-mentioned results,different dose rate runtime the dose distribution and no significant difference Mapcheck validation documented.Conclusions： The MLC leaf speed may be effect the dose distribution of intensity-modulated radiotherapy.In spite of treatment the effect is very weak in clinical practice,but this method can be used as a routine QA method for linear accelerator and treatment planning system with SW-IMRT.