二级准直器在鼻咽癌容积调强放射治疗计划设计中的应用研究

Application of Liner-accelerator Two-degrade Collimator in the Treatment of Nasopharyngeal Carcinoma with Volumetric Modulated Arc Therapy

目的比较治疗计划系统二级准直器(MLC)角度选择对容积调强放射治疗(VMAT)计划质量与运行效率的影响,探索治疗计划设计的优化方案。方法随机选取2013年3月-12月治疗的20例鼻咽癌患者,设定不同的MLC角度,进行同步加量的VMAT逆向计划设计,比较MLC角度对靶区和危及器官剂量分布、机器输出跳数的差异。MLC角度分别设置为0、15、30、45、60°。结果随着MLC角度增大,靶区适形指数和均匀性指数有变差的趋势,0°和15°计划相对最优,45°和60°计划对危机器官的保护不如其他角度好而且机器跳数明显增加。结论改变MLC角度对治疗计划会产生明显影响,随MLC角度增加,计划质量与运行效率均有变差的趋势,但是小范围改变MLC角度理论上可以降低漏射线对人体的影响。

Objective Compare the two-degrade collimator（MLC） angle selection＇s impact on plan quality and operational efficiency for volumetric intensity-modulated radiotherapy（VMAT） in the treatment planning system,and to explore the scheme for treatment plan optimization.Methods Twenty patients with nasopharyngeal carcinoma underwent the treatment between March and December 2013 were randomly selected and planned for SIB-VMAT treatment with different parameters set in the range of 0- 60° with 15° interval for collimator angles.Planned dose distribution to the target volumes,organs at risk,and monitor units were compared.Results As the MLC angle increased,target conformal index and homogeneity index had a trend to became deteriorated.The optimal plans were 0° and 15°,while 45° and 60° plans gave poor protection for the organ at risk compare to other angle plans and the monitor units were significantly increased.Conclusion Change the MLC angle had visible impact on treatment plans,there was a trend to deteriorate with the MLC angle increased,but small changes in MLC angle range can theoretically reduce the influence from leakage radiation on the human body.