基于EPID宫颈癌IMRT验证的不同Gamma通过率参数影响分析

目的:使用Varian 非晶硅电子射野影像系统（EPID）对80例宫颈癌术后患者的放疗计划进行Gamma通过率验证，分析不同机架角度、两台同型号加速器间Gamma通过率的差异；探讨3种参数设置对Gamma通过率的影响，为计划验证提供理论依据。方法:对每一患者制定7野均分治疗计划并创建验证计划，在两台相同型号的Varian Unique（1、2）加速器上进行验证并获取验证图像；通过Portal Dosimetry（PD）软件获得不同参数设置（标准剂量差异与距离符合度）下的Gamma通过率，对其进行统计学分析。结果:参数设置分别为PD_Global/PD_Local 1%/1 mm、2%/2 mm、3%/3 mm，剂量阈值10%。（1）当参数为PD_Global（2%/2 mm、1%/1 mm）时，Gan=0°的Gamma通过率优于其他角度；Gan=104°、256°的Gamma通过率低于其他角度（P<0.05）。参数为PD_Local（3%/3 mm、2%/2 mm、1%/1 mm）时，Gan=0°的Gamma通过率低于其他角度（P<0.05）。（2）参数为PD_Global 1%/1 mm、PD_Local 1%/1 mm时，Unique-2的Gamma通过率高于Unique-1（P<0.05）。结论:严格的参数设置能够体现机架角度、加速器性能等对Gamma通过率的影响；针对不同部位的肿瘤需要加入相关的分析条件。为提高放疗的精确性，物理师需要增加对射野影像装置、机架角位移、多叶准直器到位精度等设备参数的检测频率，并通过大量数据的累积与临床相结合，制定更严格的Gamma通过率参数与限值。

Effects of different parameter settings on Gamma passing rate in EPID-based IMRT verification for cervical cancer

Abstract: Objective To verify the Gamma passing rates of radiotherapy plans in 80 patients with cervical cancer after operation using Varian electronic portal imaging device (EPID) for analyzing differences in Gamma passing rates between two accelerators and different gantry angles, and to discuss the effects of 3 different parameter settings on the Gamma passing rate, thereby providing a practical theoretical basis for plan verification. Methods Seven-field treatment plan was developed for each patient, and the corresponding verification plan was created. Plans were verified at two accelerators of the same type (Varian Unique 1, 2), and verification images were also obtained. Portal Dosimetry (PD) was used to obtain the Gamma passing rates under different parameter settings (standard dose difference and distance to agreement), and then the obtained Gamma passing rates were statistically analyzed. Results Parameter settings included PD_Global/PD_Local 1%/1 mm, 2%/2 mm, 3%/3 mm, with a dose threshold of 10%. (1) When the parameter was set as PD_Global（2%/2 mm, 1%/1 mm), the Gamma passing rate of Gan=0° was the highest and the Gamma passing rates of Gan=104°, 256° were lower than others (P<0. 05). The Gamma passing rate of Gan=0° was the lowest when adopting PD_Local (3%/3 mm, 2%/2 mm, 1%/1 mm) (P<0.05). (2) When the parameter was set as PD_Global 1%/1 mm and PD_Local 1%/1 mm, the Gamma passing rate of Unique-2 was higher than that of Unique-1 (P<0.05). Conclusion Strict parameter setting can reflects the effect of gantry angle, accelerator performance on Gamma passing rate. Relevant analytical conditions should be added for different tumor sites. In order to improve radiotherapy accuracy, physicists need to increase the detection frequency of the equipment parameters such as imaging devices, gantry angular displacement, multileaf collimator positioning accuracy, and stricter parameters and limits of Gamma passing rate should be established through the accumulation of large amounts of data and combination with clinical information.