Department of Radiation Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, 440 Jiyan Road, Jinan, 250117, Shandong, China.
Radiat Oncol. 2022 Jul 16;17(1):123. doi: 10.1186/s13014-022-02097-0.
The study evaluated the differences in leaf positioning deviations by the log files of three advanced accelerators with two delivery techniques, and established specific assessment parameters of leaf positioning deviations for different types of accelerators.
A total of 420 treatment plans with 5 consecutive treatment log files were collected from the Trilogy, TrueBeam and Halcyon accelerators. Millennium MLC was equipped on the Trilogy and TrueBeam accelerators. A jawless design and dual-layer MLC were adopted on the Halcyon accelerator. 70 IMRT and 70 VMAT plans were selected randomly on each accelerator. The treatment sites of all plans included head and neck, chest, breast, pelvis and other sites. The parsing tasks for 2100 log files were proceeded by SunCheck software from Sun Nuclear Corporation. The maximum leaf root mean square (RMS) errors, 95th percentile errors and percentages of different leaf positioning errors were statistically analyzed. The correlations between these evaluation parameters and accelerator performance parameters (maximum leaf speed, mean leaf speed, gantry and arc angle) were analyzed.
The average maximum leaf RMS errors of the Trilogy in the IMRT and VMAT plans were 0.44 ± 0.09 mm and 0.79 ± 0.07 mm, respectively, which were higher than the TrueBeam's 0.03 ± 0.01 mm, 0.03 ± 0.01 mm and the Halcyon's 0.05 ± 0.01 mm, 0.07 ± 0.01 mm. Similar data results were shown in the 95th percentile error. The maximum leaf RMS errors were strongly correlated with the 95th percentile errors (Pearson index > 0.5). The leaf positioning deviations in VMAT were higher than those in IMRT for all accelerators. In TrueBeam and Halcyon, leaf position errors above 1 mm were not found in IMRT and VMAT plans. The main influencing factor of leaf positioning deviation was the leaf speed, which has no strong correlation with gantry and arc angles.
Compared with the quality assurance guidelines, the MLC positioning deviations tolerances of the three accelerators should be tightened. For both IMRT and VMAT techniques, the 95th percentile error and the maximum RMS error are suggested to be tightened to 1.5 and 1 mm respectively for the Trilogy accelerator. In TrueBeam and Halcyon accelerators, the 95th percentile error and maximum RMS error of 1 and 0.5 mm, respectively, are considered appropriate.
本研究通过三种先进加速器的两种治疗技术的日志文件，评估叶片定位偏差的差异，并为不同类型的加速器建立叶片定位偏差的具体评估参数。
从 Trilogy、TrueBeam 和 Halcyon 加速器中收集了总计 420 个治疗计划和 5 个连续的治疗日志文件。Trilogy 和 TrueBeam 加速器配备了 Millennium MLC。Halcyon 加速器采用无框设计和双层 MLC。在每个加速器上随机选择 70 个 IMRT 和 70 个 VMAT 计划。所有计划的治疗部位包括头颈部、胸部、乳房、骨盆和其他部位。通过 Sun Nuclear 公司的 SunCheck 软件对 2100 个日志文件进行解析任务。对最大叶片均方根（RMS）误差、95%误差和不同叶片定位误差的百分比进行了统计学分析。分析了这些评估参数与加速器性能参数（最大叶片速度、平均叶片速度、龙门架和弧形角度）之间的相关性。
在 IMRT 和 VMAT 计划中，Trilogy 的平均最大叶片 RMS 误差分别为 0.44 ± 0.09 毫米和 0.79 ± 0.07 毫米，高于 TrueBeam 的 0.03 ± 0.01 毫米、0.03 ± 0.01 毫米和 Halcyon 的 0.05 ± 0.01 毫米、0.07 ± 0.01 毫米。95%误差也有类似的数据结果。最大叶片 RMS 误差与 95%误差呈强相关性（Pearson 指数>0.5）。对于所有加速器，VMAT 的叶片定位偏差均高于 IMRT。在 TrueBeam 和 Halcyon 中，在 IMRT 和 VMAT 计划中未发现叶片位置误差大于 1 毫米。叶片定位偏差的主要影响因素是叶片速度，与龙门架和弧形角度没有很强的相关性。
与质量保证指南相比，三个加速器的 MLC 定位偏差容限应收紧。对于 IMRT 和 VMAT 技术，建议 Trilogy 加速器的 95%误差和最大 RMS 误差分别收紧至 1.5 和 1 毫米。在 TrueBeam 和 Halcyon 加速器中，分别考虑 1 和 0.5 毫米的 95%误差和最大 RMS 误差是合适的。
