鼻咽癌CDR-VMAT与ss-IMRT剂量学比较评估

目的：分别比较鼻咽癌（NPC）恒定剂量率容积调强（CDR-VMAT）方式和7野、9野静态调强（ss-IMRT）方式的计划质量及治疗效率，提供临床参考意义。方法：对10例NPC患者以相同的处方剂量，但分别采用CDR—VMAT、7野SS—IMRT和9野ss-IMRT方式设计计划。比较三组计划在剂量分布、靶区适形指数（cI）与均匀性指数（HI），不同危及器官（OAR）的剂量以及治疗计划的执行时间的差异。结果：三种执行方法均能满足临床剂量要求，与7野调强相比（7F-IMRT），恒定剂量率方式（CDR-VMAT）靶区PTV7n4最小剂量D98％略优，适形指数CI较好（p=0．006）；靶区PTV66、PTV60、PTV54的均匀性指数HI较好（p=0．010，0．003，0．032）；且靶区PTv。的最小D98％最大剂量D98％较优（P=0．022，0．036）。与9野调强（9F—IMRT）J（R比，除靶区PTV。和PTV。中位剂量D50％略低及PTV60最小剂量D98％略差外（P=0．001～0．021），其它比较参数无显著差异。危及器官方面（OrganatRiskOAR），9野调强计划中，脊髓、腮腺可以得到更好的保护（p=0．032，0．047）。CDR-VMAT和7野、9野调强计划组总机器跳数（Mu）分别为552（＋48）MU、748（＋87）和730（＋76）MU，使用CDR-VMAT方式跳数分别减少36％和32％。结论：与7野调强比较，在危及器官剂量相似的情况下，CDR-VMAT容积调强和9野调强方式均提高靶区内的剂量分布，且CDR-VMAT方式可提高治疗效率。

Comparison and Evaluation of CDR-VMAT and ss-IMRT for The Treatment of Nasophar- yngeal inDosimetry

Objectlve： To compare the constant dose rate volumetric modulated arc therapy （CDR-VMAT） and step ＆ shot intensity modulated radiation therapy （ss-IMRT） in terms of dosiemtric quality and delivery efficiency for nasopharyngeal carcinoma （NPC）. Methods：Ten NPC patients are enrolled in this study. Three treatment plans （CDR-VMAT, 7 fields IMRT and 9 fields IMRT） with same target coverage are generated for each patient. The target dose conformity and homogeneity and the dosiemtric parameters of the organ at risks （OARs） are compared. Meanwhile the delivery efficiency of the different plans are evaluated. Results：All plans can meet the clinic requirements. Compare to 7 fields IMRT plans, CDR-VMAT plans have better performance in mindose and conformity for target PTV70.4. The homogeneity index of target PTV66, PTV60 and PTV54 are lower than 7 fields IMRT plans. And CDR-VMAT plans have higher mindose and lower maxdose in target PTV6o. Compared 9 fields IMRT plans, CDR-VMAT plans have lower median dose and mindose for target PTV66, PTV54 and PTV60. The dose of spinal cord and partiods are less in 9 fields IMRT. Furthermore, the CDR-VMAT plans have 30% lower MU than ss-IMRT plans. Conclusions： Compared to 7 fields LMRT, CDR-VMAT plans have better performance in target dose coverage anddelivery efficiency.