中文摘要：

目的：探讨及评价不同准直器（Fixed/Iris）的选择对治疗计划剂量学特点的影响。方法：选取12例肝癌患者影像数据,统一给予靶区剂量50 Gy/5 F,在相同条件下分别对每例患者选择Fixed与Iris准直器进行治疗计划设计,通过靶区适形度指数（CI）、均匀性指数（HI）、梯度指数（GI）、正常肝脏平均受量以及治疗时间等参数,分析评估计划优化质量及实施效率。结果：Iris组计划执行的平均治疗时间明显优于Fix组[（48.33±1.92）min vs（51.50±1.88）min,t=4.23,P=0.001],而CI（0.79±0.07 vs 0.80±0.08,t=0.52,P=0.613）、HI（0.42±0.14 vs 0.41±0.14,t=0.35,P=0.733）、GI（3.66±0.61 vs 3.60±0.50,t=1.15,P=0.273）、处方剂量归一值[（76.92±6.55）%vs（77.00±6.34）%,t=0.18,P=0.857]以及正常肝脏平均受量[（5.15±1.25）Gy vs（5.16±1.27）Gy,t=0.63,P=0.542]则无统计学差异。结论：CyberKnife系统中使用Iris相对Fixed准直器而言,除治疗时间明显缩短外,没有显著的剂量学差异。而对于其他部位肿瘤患者的治疗计划有无差异,还需进一步探讨和研究。

英文摘要：

Objective To discuss and evaluate the effects of different collimators（Fixed/Iris） on the dosimetric parameters of treatment plans. Methods Twelve liver cancer patients were selected in the study. With the same prescription dose of 50 Gy/5 f given to target areas, the treatment plan of each patient was designed using Fixed and Iris collimators, respectively. The target conformity index（CI）, homogeneity index（HI）, gradient index（GI）, mean dose of normal liver and treatment time were analyzed to evaluate the optimization quality and the delivery efficiency. Results The average treatment time of the plans with Iris collimator was obviously better than that with Fix collimator[（48.33±1.92） min vs（51.50±1.88） min; t=4.23, P=0.001）], while no statistical differences were found in CI（0.79±0.07 vs 0.80±0.08; t=0.52, P=0.613）, HI（0.42±0.14 vs 0.41±0.14; t=0.35,P=0.733）, GI（3.66±0.61 vs 3.60±0.50; t=1.15, P=0.273）, the normalized mean value of prescription dose[（76.92±6.55）% vs（77.00±6.34）%; t=0.18, P=0.857], and the mean dose of normal liver[（5.15±1.25） Gy vs（5.16±1.27） Gy; t=0.63, P=0.542].Conclusion For CyberKnife system, the treatment time of plans using Iris collimator is significantly shorter than those of the plans using Fixed collimator, but no obvious differences were found in dosimetric parameters between the two plans. The further discussion and study are necessary to compare the effects of plans using Iris/Fixed collimator for the patients with other cancers.