AlignRT引导联合开放式面罩的头部肿瘤放疗摆位流程与误差分析

目的 提出一种基于光学体表追踪系统AlignRT联合开放式面罩的头部肿瘤无标记线全疗程摆位流程，评估摆位时间和重复摆位次数，并对比分析AlignRT与锥形束CT （cone beam CT，CBCT）两者之间摆位误差的差异、相关性和一致性。方法 回顾性分析33例132分次开放式面罩固定头部肿瘤患者摆位误差数据，全疗程放疗使用AlignRT引导无标记线摆位并以治疗计划系统中自动生成的外轮廓（Body）结构作为参考体表，结束摆位后分别获取AlignRT与CBCT两种系统的左右（x轴）、升降（y轴）、进出（z轴）、床旋转（Rtn）、进出倾斜（Pitch）和左右转动（Roll）6维方向摆位误差，并记录摆位时间与重复摆位次数。分别采用Wilcoxon和Spearman法分析两种系统摆位误差的差异和相关性；应用Bland-Altman法评估两者一致性。结果 6维方向CBCT摆位误差均满足临床要求（线性方向范围-0.30~0.30 cm，旋转方向范围-2.0°~2.0°），摆位时间为（98±31） s，重复摆位次数占比1.51%（2/132）。两种系统摆位误差除x （Z=-3.11，P=0.002）、y （Z=-7.40，P<0.001）和Pitch （Z=-4.48，P<0.001）外差异均无统计学意义。摆位误差除z方向外，x （r_s=0.47，P<0.001）、y （r_s=0.29，P=0.001）、Rtn （r_s=0.47，P<0.001）、Pitch （r_s=0.28，P=0.001）和Roll （r_s=0.45，P<0.001）均呈正相关。6维方向摆位误差95%一致性界限（95% LoA）分别为-0.12~0.09 cm、-0.07~0.17 cm、-0.19~0.20 cm、-1.0°~0.9°、-1.0°~1.5°和-0.9°~1.0°，95%一致性界限的95%可信区间（95%CI）分别为-0.14~0.11 cm、-0.09~0.19 cm、-0.23~0.23 cm、-1.2°~1.1°、-1.2°~1.7°和-1.0°~1.1°，均位于临床摆位误差容许范围之内。6维方向摆位误差差值3.41%（27/792<5%）在95% LoA之外。在95% LoA范围内，差值绝对值的最大值分别为0.12、0.16、0.19 cm、0.9°、1.5°和1.0°。结论 基于AlignRT联合开放式面罩的头部肿瘤无标记线全疗程摆位流程，使AlignRT与CBCT摆位误差具有一定的相关性和一致性，摆位效率尚可，可应用于首次治疗，并实现治疗中实时监测提高安全性，具有临床应用价值。

Workflow and error analyses of patient setup based on open-face mask immobilization combined with AlignRT for head tumor radiotherapy

Objective To propose a markless patient setup workflow based on the optical surface monitoring system (AlignRT) and open-face mask immobilization for whole-course head tumor radiotherapy, assess the setup time and repositioning frequency of the proposed workflow, and conduct a comparative analysis of the differences, correlation, and consistency of the setup errors of the AlignRT and cone beam CT (CBCT) systems.Methods A retrospective analysis was conducted for the data on the errors of 132 fractionated setup based on open-face mask immobilization of 33 head tumor patients. AlignRT-guided markless patient setup workflow was applied throughout the radiotherapy. Meanwhile, the body structures automatically generated by the treatment planning system were used as body references. The 6-degree-of-freedom (6DoF) setup errors (lateral, vertical, longitudinal, rotation, pitch, roll, and yaw directions), setup time, and repositioning frequency of the AlignRT and CBCT systems were recorded and analyzed. The Wilcoxon and Spearman analyses were used to statistically assess the differences and correlation of the setup errors of the two systems. Moreover, the Bland-Altman analysis was employed to evaluate the consistency of the two systems.Results The 6DoF setup errors of CBCT were within the clinical tolerance (linear motions:-0.30 to 0.30 cm; rotational motions:-2.0° to 2.0°). The setup time and repositioning frequency of CBCT were (98 ±31) s and 1.51% (2/132), respectively. There was no significant difference in setup errors between the two systems except those in x-axis (Z=-3.11, P=0.002), y-axis (Z=-7.40, P<0.001), and Pitch (Z=-4.48, P<0.001). There was a significant positive correlation between the setup errors along lateral (r_s=0.47, P<0.001) and vertical (r_s=0.29, P=0.001) directions, rotation (Rtn; r_s=0.47, P<0.001), pitch (Pitch; r_s=0.28, P=0.001) and roll (Roll; r_s=0.45, P<0.001) of the two systems. The 95% limits of agreement (95% LoA) of 6DoF setup errors were -0.12 to 0.09 cm, -0.07 to 0.17 cm, -0.19 to 0.20 cm, -1.0° to 0.9 °, -1.0° to 1.5°, and -0.9° to 1.0°, respectively. The 95% confidence interval (95% CI) of 95% LoA was -0.14 to 0.11 cm, -0.09 to 0.19 cm, -0.23 to 0.23 cm, -1.2° to 1.1°, -1.2° to 1.7°, and-1.0° to 1.1°, respectively, all of which were within the permissible error ranges. The 6DoF setup error difference of 3.41% (27/792< 5%) was beyond the 95% LoA. The maximum absolute differences of 6DoF setup errors within the 95% LoA were 0.12, 0.16, 0.19 cm, 0.9°, 1.5°, and 1.0°, respectively.Conclusions The proposed markless setup workflow based on AlignRT combined with open-face mask immobilization for whole-course head tumor radiotherapy exhibits reasonable agreement and consistency with the patient setup using CBCT, with acceptable clinical efficiency. It can be applied to the first radiotherapy and the real-time monitoring of therapy to improve the safety and thus is of value in clinical applications.