From phase-based to displacement-based gating: a software tool to facilitate respiration-gated radiation treatment
From phase-based to displacement-based gating: a software tool to facilitate respiration-gated radiation treatment
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DOI：
10.1120/jacmp.v10i4.2982
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发表时间：
2009-01-01
影响因子：
2.1
通讯作者：
Mageras, Gig S.
中科院分区：
文献类型：
--
作者：
Santoro, Joseph P.;Yorke, Ellen;Mageras, Gig S.
Varian实时位置管理（RPM）系统允许基于呼吸波形的相位或位移（振幅）进行呼吸门控。临床应用中的一个问题是，呼吸相关（4D-CT）模拟所需的基于相位的门控对于治疗期间的不规则呼吸模式不稳健，并且广泛使用的系统版本（1.6）没有提供从基于相位的门控改变为等效的基于位移的门控的简单方法。我们报告的发展和评价的一个强大的方法转换相位门阈值，由医生设置，到等效的位移门阈值，以促进其临床应用治疗。软件工具分析4D-CT模拟期间记录的呼吸轨迹，并通过函数拟合确定位移和相位之间的关系。位移门阈值由该函数的两个值的平均值确定，对应于原始相位门的开始和结束阈值。通过两种方式对软件工具进行评价：第一，在4D-CT模拟期间，位移门控和相位门控之间的门内残留目标运动和预测治疗射束占空比是否等效（使用回顾性相位重新计算）;第二，相对于相位门控，治疗期间的位移门控是否改善了残留运动（使用实时相位计算）。从呼吸轨迹中推断出残余目标运动，并根据相对于记录轨迹开始时的值测量的门内位移的平均值和标准差进行量化。对于回顾性计算的呼吸轨迹与实时计算的呼吸轨迹相比，我们通过测量每个轨迹中的相位门位置以及平均门内位移和位移的标准差来评估实时相位计算的不准确性。对10例患者的回顾性计算数据进行了分析。患者平均门控内平均值+/-标准差位移（代表残余运动）从模拟条件下相位门控的0.16 +/- 0.14 cm降至位移门控的0.12 +/- 0.08 cm。治疗条件下的呼吸轨迹评价（实时相位计算）表明，平均位移门阈值导致所有研究患者的门内平均值和残余运动（方差）较低。患者平均门内平均值+/-标准差位移从相位门控（治疗条件下）的0.26 +/- 0.18 cm减少到位移门控的0.15 +/- 0.09 cm。当呼吸轨迹不规则时，实时相位门控有时会导致在呼吸周期的不正确部分上进行门控。位移门控不太容易出现这种错误，这可以从大多数情况下门控内的残余运动较低得到证明。在占空比和残余运动方面，基于位移的选通等同于基于相位的选通，用于追溯计算的相位信息。
The Varian Real-time Position Management (RPM) system allows respiratory gating based on either the phase or displacement (amplitude) of the breathing waveform. A problem in clinical application is that phase-based gating, required for respiration-correlated (4D-CT) simulation, is not robust to irregular breathing patterns during treatment, and a widely used system version (1.6) does not provide an easy means to change from a phase-based gate into an equivalent displacement-based one. We report on the development and evaluation of a robust method to convert phase-gate thresholds, set by the physician, into equivalent displacement-gate thresholds to facilitate its clinical application to treatment. The software tool analyzes the respiration trace recorded during the 4D-CT simulation, and determines a relationship between displacement and phase through a functional fit. The displacement gate thresholds are determined from an average of two values of this function, corresponding to the start and end thresholds of the original phase gate. The software tool was evaluated in two ways: first, whether in-gate residual target motion and predicted treatment beam duty cycle are equivalent between displacement gating and phase gating during 4D-CT simulation (using retrospective phase recalculation); second, whether residual motion is improved with displacement gating during treatment relative to phase gating (using real-time phase calculation). Residual target motion was inferred from the respiration traces and quantified in terms of mean and standard deviation in-gate displacement measured relative to the value at the start of the recorded trace. For retrospectively-calculated breathing traces compared with real-time calculated breathing traces, we evaluate the inaccuracies of real-time phase calculation by measuring the phase gate position in each trace as well as the mean in-gate displacement and standard deviation of the displacement. Retrospectively-calculated data from ten patients were analyzed. The patient averaged in-gate mean +/- standard deviation displacement (representing residual motion) was reduced from 0.16 +/- 0.14 cm for phase gating under simulation conditions to 0.12 +/- 0.08 cm for displacement gating. Evaluation of respiration traces under treatment conditions (real-time phase calculation) showed that the average displacement gate threshold results in a lower in-gate mean and residual motion (variance) for all patients studied. The patient-averaged in-gate mean +/- standard deviation displacement was reduced from 0.26 +/- 0.18 cm for phase gating (under treatment conditions) to 0.15 +/- 0.09 cm for displacement gating. Real-time phase gating sometimes leads to gating on incorrect portions of the breathing cycle when the breathing trace is irregular. Displacement gating is less prone to such errors, as evidenced by the lower in-gate residual motion in a large majority of cases. In terms of duty cycle and residual motion, displacement-based gating is equivalent to phase-based gating for retrospectively-calculated phase information.