Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
GenesisCareUS, Madison Heights, MI, USA.
J Appl Clin Med Phys. 2021 Jul;22(7):121-127. doi: 10.1002/acm2.13281. Epub 2021 May 27.
Establish and compare two metrics for monitoring beam energy changes in the Halcyon platform and evaluate the accuracy of these metrics across multiple Halcyon linacs.
The first energy metric is derived from the diagonal normalized flatness (F ), which is defined as the ratio of the average measurements at a fixed off-axis equal distance along the open profiles in two diagonals to the measurement at the central axis with an ionization chamber array (ICA). The second energy metric comes from the area ratio (AR) of the quad wedge (QW) profiles measured with the QW on the top of the ICA. Beam energy is changed by adjusting the magnetron current in a non-clinical Halcyon. With D measured in water at each beam energy, the relationships between F or AR energy metrics to D in water is established with linear regression across six energy settings. The coefficients from these regressions allow D (F ) calculation from F using open profiles and D (QW) calculation from AR using QW profiles.
Five Halcyon linacs from five institutions were used to evaluate the accuracy of the D (F ) and the D (QW) energy metrics by comparing to the D values computed from the treatment planning system (TPS) and D measured in water. For the five linacs, the D (F ) reported by the ICA based on F from open profiles agreed with that calculated by TPS within -0.29 ± 0.23% and 0.61% maximum discrepancy; the D (QW) reported by the QW profiles agreed with that calculated by TPS within -0.82 ± 1.27% and -2.43% maximum discrepancy.
The F -based energy metric D (F ) can be used for acceptance testing of beam energy, and also for the verification of energy in periodic quality assurance (QA) processes.
建立并比较两种用于监测 Halcyon 平台中射束能量变化的指标，并评估这些指标在多个 Halcyon 直线加速器中的准确性。
第一个能量指标源自对角归一化平坦度（F），其定义为在两个对角线上沿开放轮廓在固定离轴等距离处的平均测量值与在中央轴处使用电离室阵列（ICA）的测量值之比。第二个能量指标来自使用 ICA 顶部的四楔形（QW）测量的 QW 轮廓的面积比（AR）。通过调整非临床 Halcyon 中的磁控管电流来改变束能。在每个束能下用 D 测量水，通过线性回归在六个能量设置中建立 F 或 AR 能量指标与水中的 D 之间的关系。这些回归的系数允许使用开放轮廓从 F 计算 D（F），并使用 QW 轮廓从 AR 计算 D（QW）。
来自五个机构的五台 Halcyon 直线加速器用于通过与从治疗计划系统（TPS）计算的 D 值和在水中测量的 D 值进行比较来评估 D（F）和 D（QW）能量指标的准确性。对于这五台直线加速器，基于开放轮廓中 F 计算的 ICA 报告的 D（F）与 TPS 计算的结果在-0.29 ± 0.23%和 0.61%最大差异范围内一致；QW 轮廓报告的 D（QW）与 TPS 计算的结果在-0.82 ± 1.27%和-2.43%最大差异范围内一致。
基于 F 的能量指标 D（F）可用于束能的验收测试，也可用于周期性质量保证（QA）过程中的能量验证。
