Ozdemir Sevim, Coban Yasin, Akin Mustafa, Ambarcioglu Pinar, Onay Ozgehan, Yildirim Cumhur, Uzel Esengul, Uzel Omer
Cerrahpasa Medical Faculty, Department of Radiation Oncology, Istanbul, Turkey.
J BUON. 2014 Oct-Dec;19(4):953-7.
To evaluate the performance of volumetric arc therapy (VMAT), dynamic intensity modulated radiotherapy (IMRT) and step-and-shoot IMRT techniques in nasopharyngeal cancer (NPC) patients.
IMRT plans of 48 NPC patients treated between May 2010 and December 2012, were evaluated. Twenty two patients were planned with VMAT, 18 with dynamic IMRT and 8 with step-and-shoot IMRT. Conformity index (CI) and homogeneity index (HI), the dosimetry of the planning target volumes (PTVs) and organs at risk (OARs) and the monitor units (MU) were evaluated for each IMRT modality.
The conformity indices of VMAT and dynamic IMRT were better than step-and-shoot IMRT plans (p<0.05). Step-and-shoot IMRT plans provided better homogeneity than VMAT (p=0.01). MUs for dynamic IMRT were much higher compared to VMAT (p<0.01) and step and- shoot IMRT (p<0.01). There was no significant difference between the 3 techniques in terms of PTV70 mean doses. When compared with step-and-shoot IMRT, VMAT and dynamic IMRT had a better sparing effect on optic nerves, eyes and optic chiasm (p<0.05). VMAT plans performed better sparing for brain stem than dynamic IMRT (p=0.01). There was a remarkable decrease in the maximum doses of VMAT to the eye.
VMAT outperforms dynamic IMRT by effectively reducing the MU and the dose to some OARs, with adequate PTV coverage. Also, VMAT provides better sparing of normal tissue and conformity than step-and-shoot IMRT. Differences between step-and-shoot IMRT and dynamic IMRT are thought to be due to technical differences of linear accelerator devices like fiber size, variable fiber, dose rate and gantry.
评估容积弧形调强放疗（VMAT）、动态调强放疗（IMRT）和静态调强放疗技术在鼻咽癌（NPC）患者中的性能。
对2010年5月至2012年12月期间接受治疗的48例NPC患者的IMRT计划进行评估。22例患者采用VMAT计划，18例采用动态IMRT计划，8例采用静态调强放疗计划。对每种IMRT模式评估适形指数（CI）和均匀性指数（HI）、计划靶区（PTV）和危及器官（OAR）的剂量学以及监测单位（MU）。
VMAT和动态IMRT的适形指数优于静态调强放疗计划（p<0.05）。静态调强放疗计划比VMAT提供更好的均匀性（p=0.01）。与VMAT（p<0.01）和静态调强放疗（p<0.01）相比，动态IMRT的MU要高得多。三种技术在PTV70平均剂量方面无显著差异。与静态调强放疗相比，VMAT和动态IMRT对视神经、眼睛和视交叉有更好的保护作用（p<0.05）。VMAT计划对脑干的保护作用比动态IMRT更好（p=0.01）。VMAT对眼睛的最大剂量有显著降低。
VMAT通过有效减少MU和对某些OAR的剂量，在充分覆盖PTV的情况下优于动态IMRT。此外，VMAT比静态调强放疗能更好地保护正常组织和适形。静态调强放疗和动态IMRT之间的差异被认为是由于直线加速器设备的技术差异，如光纤尺寸、可变光纤、剂量率和机架。
