中文摘要：

目的比较旋转容积调强放疗（VMAT）技术与固定野动态调强放疗（IMRT）技术在复发鼻咽癌应用中的剂量学差异。方法选取11例局部复发鼻咽癌患者,分别设计双弧VMAT与七野IMRT两组计划,比较两组计划的靶区（PTV）剂量参数、适形指数（CI）和均匀指数（HI）,以及危及器官（OAR）剂量参数、机器监测跳数（MU）、投照时间。结果 VMAT的PTV D98%略低于IMRT（P〈0.05）,CI高于IMRT（P〈0.05）,HI与IMRT无显著差异（P〉0.05）。VMAT中双侧颞叶的Dmean与周围正常组织的Dmean均比IMRT低（P〈0.05）,脑干的Dmean略高于IMRT（P〈0.05）,在其他危及器官两者无显著差异（P〉0.05）。VMAT的MV（672±112）明显少于IMRT（917±206）,幅度约（25±13）%（P〈0.05）,VMAT投照时间〔（2.3±0.1）min〕比IMRT〔（5.1±0.4）min〕减少（54±3）%。结论局部复发鼻咽癌VMAT计划可以达到或略优于IMRT计划的靶区剂量分布,能更好地保护双侧颞叶,有效减少MU和投照时间。

英文摘要：

Objective To compare volumetric modulated arc radiotherapy（ VMAT） technique with fixed-gantry intensity-modulated radiotherapy（ IMRT） technique based on dynamic multi-leaf collimator for locally recurrent nasopharyngeal carcinoma. Methods CT data from eleven nasopharyngeal-carcinoma patients were included. Dual-arc VMAT and 7-field IMRT plans were created for each case and were compared in terms of conformity index（ CI）,homogeneity index（ HI） of the planning target volume（ PTV）,organ-at-risk（ OAR） sparing,monitor unit（ MU）and delivery time. Results The D98%（ near-minimal dose） of PTV in the VMAT plans was slightly lower than that of the IMRT plans（ P〈0. 05）,while the CI was higher than that of the IMRT plans（ P〈0. 05）. There was no significant difference in HI between the two plans（ P〈0. 05）. Compared with the IMRT plans,the VMAT plans demonstrated lower mean doses of the bilateral temporal lobes and the whole surrounding normal tissue（ P〈0. 05）,but slightly higher Dmean（ mean dose） of brainstem（ P〈0. 05）. In terms of the other OARs,there were no significant differences found（ P〈0. 05）. The MU of VMAT plans（ 672 ±112） was significantly less than that of the IMRT plans（ 917 ±206）,by 25% ±13%（ P〈0.05）. The delivery time of the VMAT plans（ 2. 3 ± 0. 1） min was less than that of the IMRT plans（ 5. 1 ± 0. 4） min,by 54% ± 3%. Conclusions For locally recurrent nasopharyngeal carcinoma,the VMAT technique could achieve equivalent or superior dose distribution of the target and better protect the bilateral temporal lobes,compared to the IMRT technique. Moreover,it could reduce the MU and delivery time effectively.