Abstract: Objective To analyze the systematic and random errors of different treatment linear accelerators in intensity-modulated radiotherapy (IMRT) for patients with cervical cancer. Methods From October 2019 to November 2021, 320 cervical cancer patients who were 32-75 years old and received IMRT with Varian Vital_Beam accelerator and Elekta Versa_HD accelerator in Sun Yat-sen University Cancer Center were selected. After the design of the radiotherapy plan was completed, we performed the X-ray simulation positioning machine reset verification according to the bed moving parameters of the treatment plan for each patient, and used the cone beam CT (CBCT) for body position verification during the treatment, including 960 CBCT positioning error data. The body position error data after CBCT calibration were recorded and analyzed by paired t-test. Results The positioning errors of the Varian Vital_Beam and Elekta Versa_HD linear accelerators in the superior-inferior (SI), left-right (LR), and anterior-post (AP) translation directions were (0.00±0.32) cm, (0.00±0.25) cm, (0.04±0.24) cm and (0.08±0.40) cm, (0.02±0.33) cm, (0.04±0.25) cm; there were statistically significant differences in the SI and AP directions (both P<0.05), while there was no statistically significant difference in the LR direction (P> 0.05). The positioning errors of the Varian Vital_Beam and Elekta Versa_HD linear accelerators in the RTN, Pitch, and Roll rotation directions were (0.12±1.00)°, (0.81±1.33)°, (0.32±0.64)° and (0.24± 0.73)°, (0.28±1.64)°, (0.01±0.80)°; there were statistically significant differences (all P<0.05). The total systematic error errors of Varian Vital_Beam linear accelerator in the SI, LR, AP, RTN, Pitch, and Roll directions were 0.29 cm, 0.22 cm, 0.22 cm, 0.81°, 1.46°, and 0.63°; the total systematic error errors of Elekta Versa_HD linear accelerator in the SI, LR, AP, RTN, Pitch, and Roll directions were 0.37 cm, 0.30 cm, 0.23 cm, 0.69°, 1.44°, and 0.72°. The total random errors of Varian Vital_Beam linear accelerator in the SI, LR, AP, RTN, Pitch, and Roll directions were 0.23 cm, 0.18 cm, 0.14 cm, 0.98°, 0.87°, and 0.55°; the total random errors of Elekta Versa_HD linear accelerator in the SI, LR, AP, RTN, Pitch, and Roll directions were 0.28 cm, 0.23 cm, 0.15 cm, 0.54°, 1.02°, and 0.56°. Conclusions The systematic errors of different radiotherapy equipment are different. In the SI, LR, AP, and Roll directions, the systematic error of Varian Vital_Beam is smaller than that of Elekta Versa_HD; while in the RTN and Pitch directions, the systematic error of Varian Vital_Beam is greater than that of Elekta Versa_HD.

Key words: Systematic error, Linear accelerator, CBCT, Cervical cancer

摘要： 目的 分析宫颈癌患者调强放疗（intensity-modulated radiotherapy，IMRT）中不同的治疗直线加速器存在的系统误差与随机误差。方法 选择2019年10月至2021年11月在中山大学肿瘤防治中心 Varian Vital_Beam 加速器和 Elekta Versa_HD 加速器接受IMRT的宫颈癌患者 320 例，年龄 32~75岁。每例患者在放疗计划设计完成后，按照治疗计划的移床参数进行X线模拟定位机复位验证，治疗实施时，使用锥形束CT（cone beam CT，CBCT）进行体位验证，共 960次CBCT摆位误差数据。记录并观察 CBCT 校准后的体位误差数据并分别进行配对 t 检验分析。结果 Varian Vital_Beam 和 Elekta Versa_HD直线加速器在头脚SI、左右LR、前后AP平移方向的摆位误差分别为（0.00±0.32）cm、 （0.00±0.25）cm、（0.04±0.24）cm和（0.08±0.40）cm、（0.02±0.33）cm、（0.04±0.25）cm，头脚SI与前后AP两个方向差异均有统计学意义（均 P<0.05），左右LR方向差异无统计学意义（P>0.05）。 Varian Vital_Beam 和 Elekta Versa_HD 直线加速器在冠状 RTN、矢状 Pitch、横断 Roll 旋转方向的摆位误差分 别为（-0.12±1.00）°、（0.81±1.33）°、（-0.32±0.64）°和（0.24±0.73）°、（0.28±1.64）°、（-0.01±0.80）°，差异均有统计学意义（均 P<0.05）。总的系统误差：Varian Vital_Beam 各方向为头脚 SI 0.29 cm、左右 LR 0.22 cm、前后AP 0.22 cm、冠状RTN 0.81°、矢状Pitch 1.46°、横断Roll 0.63°；Elekta Versa_HD各方向为头脚 SI 0.37 cm、左右 LR 0.30 cm、前后 AP 0.23 cm、冠状 RTN 0.69°、矢状 Pitch 1.44°、横断 Roll 0.72°。 总的随机误差：Varian Vital_Beam 各方向为头脚 SI 0.23 cm、左右 LR 0.18 cm、前后 AP 0.14 cm、 冠状 RTN 0.98°、矢状 Pitch 0.87°、横断 Roll 0.55°；Elekta Versa_HD 各方向为头脚 SI 0.28 cm、左 右 LR 0.23 cm、前后 AP 0.15 cm、冠状 RTN 0.54°、矢状 Pitch 1.02°、横断 Roll 0.56°。结论 不同放疗设备存在的系统误差有所差异，在头脚 SI、左右 LR、前后 AP、横断 Roll 方向的分析中，Varian Vital_Beam 的系统误差小于 Elekta Versa_HD 的系统误差；而冠状 RTN、矢状Pitch旋转方向的系统误 差大于Elekta Versa_HD的系统误差。

关键词: 系统误差, 直线加速器, CBCT, 宫颈癌