单双弧设定对胸段食管癌容积旋转调强计划的剂量学比较

Dosimetric Comparison of Single-Arc and Double-Arc VMAT Plan for Treatment of Thoracic Esophageal Cancer

目的探讨胸段食管癌容积旋转调强(Volumetic Modulation Arc Therapy,VMAT)放疗计划设计时,单双弧设定对计划剂量的影响。方法选取2016~2017年间收治的11例病理确诊的局部晚期胸段食管癌,在Monaco 5.11 TPS计划系统中分别设计制定360°单弧VMAT(VMAT1)和双弧VMAT(VMAT2)两种放疗计划,比较两组计划靶区的剂量分布以及危及器官(Organs at Risk,OAR)受照剂量,并比较计划在加速器上的执行效率。结果两种VMAT计划的靶区剂量均能满足临床处方要求,但双弧计划VMAT2在靶区覆盖率和剂量分布均匀性均优于单弧计划VMAT1(P<0.05)。在OAR方面,两种VMAT计划中双肺的V_(20)的剂量差异有统计学意义(P<0.05),但其他剂量学指标如双肺的V_5、V_(10)和V_(30),心脏的V_(30)和V_(40)以及脊髓的D_(max)并无明显差异(P>0.05)。在执行效率方面,单弧VMAT1计划机器跳数比双弧VMAT2计划的显著减少,治疗时间也明显缩短(P<0.05)。结论单弧计划虽在靶区覆盖率和均匀性方面差于双弧计划的,但显著减少了治疗时间,执行效率最高。因此对于胸段食管癌容积旋转调强放疗来说,推荐选择单弧计划即可。

Objective To explore the dosimetric characteristics of single arc and double arc volumetic modulation arc therapy(VMAT)for thoracic esophageal cancer.Methods Eleven thoracic esophageal cancer patients confirmed by pathology were reviewed and analyzed in the Monaco5.11treatment planning system(TPS).In this study,single arc VMAT(VMAT1)and double arc VMAT(VMAT2)plans were generated for each patient.The dose distribution to target and organs at risk(OAR),monitor units(MU)and delivery time were all recorded as dosimetric indices for plan comparison.Results The targets could meet the requirements of clinical prescription in two kinds of VMAT plans.The VMAT2plan was superior to VMAT1plan concerning target coverage and dose heterogeneity,and the difference had statistical significance(P<0.05).Compared with VMAT1plan,the whole lung dose difference of V20in VMAT2plan had statistical significance(P<0.05),while the volume V5,V10,V30of whole lung,V30,V40of heart and the Dmax to spinal cord had no statistical significance(P<0.05).In terms of execution efficiency,the number of MUs in VMAT1plan was significantly reduced and the delivery time was significantly shortened(P<0.05),comparing with VMAT2plan.Conclusion Although the single-arc VMAT plan is worse than double-arc VMAT plan in terms of target coverage and dose heterogeneity,the treatment delivery time is significantly reduced and the implementation efficiency is highest.Therefore,it is recommended to choose single-arc VMAT plan for thoracic esophageal cancer.