A novel method for quantification of beam's-eye-view tumor tracking performance.
A novel method for quantification of beam's-eye-view tumor tracking performance.
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DOI：
10.1002/mp.12572
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发表时间：
2017-11
期刊：
影响因子：
3.8
通讯作者：
Berbeco R
中科院分区：
文献类型：
--
作者：
Hu YH;Myronakis M;Rottmann J;Wang A;Morf D;Shedlock D;Baturin P;Star-Lack J;Berbeco R
使用电子射野成像设备 (EPID) 进行的治疗中成像可用于确认患者和肿瘤的位置。使用当前数字兆伏 (MV) 成像仪的实时肿瘤跟踪性能因图像质量差而受到阻碍。新颖的 EPID 设计可能有助于改善量子噪声响应，同时还保持当前临床探测器的高空间分辨率。最近研究的 EPID 设计改进包括但不限于多层成像器 (MLI) 架构、厚晶体和非晶闪烁体以及磷光体像素化和聚焦。本研究的目标是提供一种量化跟踪性能改进的方法，并揭示影响跟踪质量的探测器设计的物理基础。该研究采用了一种可推广的理想观察者方法来量化肿瘤跟踪性能。该分析用于研究增加闪烁体厚度对标准单层成像器 (SLI) 设计的影响以及 MLI 架构对跟踪性能的影响。本研究使用理想观察者信噪比 (d′) 作为跟踪性能的替代指标。我们采用对临床相关任务进行建模的函数和广义频域成像指标来将图像质量与肿瘤跟踪联系起来。相关笛卡尔形状（即球体和圆柱体）的检测任务用于量化使用基准标记的案例的可跟踪性。自动肺肿瘤跟踪算法通常利用良性和恶性肺组织纹理的差异。这些类型的算法（例如软组织定位 - STiL）通过设计判别任务进行模拟，该任务量化组织纹理的差异，通过实验测量并使用一组患者肺部的 MV 图像拟合为趋势幂律（指数为 β）。建模的 MTF 和 NPS 用于研究闪烁体厚度和 MLI 架构对肿瘤跟踪性能的影响。将肺组织的 MV 图像量化为频率的逆幂律，对于良性和恶性组织分别产生指数值 β = 3.11 和 3.29。研究发现，有基准点和无基准点的跟踪性能通常受到量子噪声的限制，而量子噪声是量子探测效率 (QDE) 的主导因素。对于通用 SLI 结构，将闪烁体厚度（硫氧化钆 - GOS）从标准 290 μm 增加到 1720 μm，可将噪声降低约 10%。然而，在 290 至 1000 μm 之间，这种减少量减少了 81%。在比较具有等效单个 GOS 层厚度的 MLI 和 SLI 探测器时，噪声的改善等于探测器中的层数（即 4），而 MTF 几乎没有差异。此外，跟踪性能的改进略小于噪声降低的平方根，约为 84-90%。将 MLI 探测器与具有等效总厚度的 SLI 和 GOS 闪烁体进行比较，物体可探测性提高约 34-39%。我们提出了一种量化肿瘤跟踪质量的新方法，并应用该模型来评估 SLI 和 MLI EPID 设计的性能。我们表明，跟踪质量的提高主要受到 NPS 改进的限制。与非常厚的闪烁体 SLI 相比，采用 MLI 架构在 QDE 中表现出相同的增益，但通过减轻光学 Swank 噪声的影响，可以在跟踪性能方面获得更显着的改进。
In-treatment imaging using an electronic portal imaging device (EPID) can be used to confirm patient and tumor positioning. Real-time tumor tracking performance using current digital megavolt (MV) imagers is hindered by poor image quality. Novel EPID designs may help to improve quantum noise response, while also preserving the high spatial resolution of the current clinical detector. Recently investigated EPID design improvements include but are not limited to multi-layer imager (MLI) architecture, thick crystalline and amorphous scintillators, and phosphor pixilation and focusing. The goal of the present study was to provide a method of quantifying improvement in tracking performance as well as to reveal the physical underpinnings of detector design that impact tracking quality. The study employs a generalizable ideal observer methodology for the quantification of tumor tracking performance. The analysis is applied to study both the effect of increasing scintillator thickness on a standard, single-layer imager (SLI) design as well as the effect of MLI architecture on tracking performance. The present study uses the ideal observer signal-to-noise ratio (d′) as a surrogate for tracking performance. We employ functions which model clinically relevant tasks and generalized frequency-domain imaging metrics to connect image quality with tumor tracking. A detection task for relevant Cartesian shapes (i.e. spheres and cylinders) was used to quantify trackability of cases employing fiducial markers. Automated lung tumor tracking algorithms often leverage the differences in benign and malignant lung tissue textures. These types of algorithms (e.g. soft tissue localization – STiL) were simulated by designing a discrimination task, which quantifies the differentiation of tissue textures, measured experimentally and fit as a power-law in trend (with exponent β) using a cohort of MV images of patient lungs. The modeled MTF and NPS were used to investigate the effect of scintillator thickness and MLI architecture on tumor tracking performance. Quantification of MV images of lung tissue as an inverse power-law with respect to frequency yields exponent values of β = 3.11 and 3.29 for benign and malignant tissues, respectively. Tracking performance with and without fiducials was found to be generally limited by quantum noise, a factor dominated by quantum detective efficiency (QDE). For generic SLI construction, increasing the scintillator thickness (gadolinium oxysulfide – GOS) from a standard 290 μm to 1720 μm reduces noise to about 10%. However, 81% of this reduction is appreciated between 290 and 1000 μm. In comparing MLI and SLI detectors of equivalent individual GOS layer thickness, the improvement in noise is equal to the number of layers in the detector (i.e. 4) with almost no difference in MTF. Further, improvement in tracking performance was slightly less than the square-root of the reduction in noise, approximately 84–90%. In comparing an MLI detector with an SLI with a GOS scintillator of equivalent total thickness, improvement in object detectability is approximately 34–39%. We have presented a novel method for quantification of tumor tracking quality and have applied this model to evaluate the performance of SLI and MLI EPID designs. We showed that improved tracking quality is primarily limited by improvements in NPS. When compared to very thick scintillator SLI, employing MLI architecture exhibits the same gains in QDE, but by mitigating the effect of optical Swank noise, results in more dramatic improvements in tracking performance.
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影响因子：
3.8
作者：
Bochud, FO;Valley, JF;Schnyder, P
通讯作者：
Schnyder, P
影响因子：
3.8
作者：
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影响因子：
3.5
作者：
CALDWELL, CB;STAPLETON, SJ;YAFFE, MJ
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YAFFE, MJ
影响因子：
3.5
作者：
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通讯作者：
McDonough, James E.
影响因子：
3.5
作者：
DESPONDS, L;DEPEURSINGE, C;VALLEY, JF
通讯作者：
VALLEY, JF