A dedicated two dimensional antiscatter grid for CBCT in radiation therapy

项目摘要 散射辐射仍然是CBCT成像中的一个主要问题，它降低了软组织的可视化 和定量的准确性。在图像引导放射治疗(IGRT)中，CBCT图像质量因散射而变差 破坏患者设置校正的准确性，并阻止在放射治疗(RT)剂量中使用CBCT 计算和自动组织分割。尤其是后一个问题是实现 患者特定的适应性放射治疗，从而在治疗过程中修改治疗计划 治疗期间对肿瘤和正常组织解剖变化的反应。为了缓解分散问题， 基于软件的散射校正方法和基于硬件的散射抑制装置，例如 射线反散射网格(ASGs)在过去的十年中得到了广泛的研究。然而，所需的 CT数(Hounsfield单位)的准确性和低对比度敏感度的改善尚未实现。 因此，为了克服现有散射抑制方法的不足，我们将开发一种新的散射抑制方法 散射抑制装置是一种用于CBCT系统的二维聚焦反散射网格(2D ASG) 在IGRT中使用。众所周知，2D阵列相对于射线照相ASG的散射抑制优势。 然而，还没有构建具有良好的初级X射线传输特性的2D ASG 可以使用标准的制造工艺来实现。为了应对这一挑战，我们将采用3D打印 技术，用钨建造2D ASG。通过使用3D打印，2D ASG的间隔厚度将被 大大减少，每个通孔将精确对准X射线焦点。此外， 铝或纤维间隔间隔物，如在射线照相ASG中，将由于机械 钨2D阵列的强度。 我们假设建议的设计将使软组织结构得到显著增强。 可视化，并将大大减少CT数值计算的不准确性，因为它的原始值很高 传输级别和高效的散射抑制能力。为了验证我们的假设，我们将(1)模拟和 利用3D打印技术构建2D ASG原型，并表征其信号传输特性， (2)评估2D ASG对CBCT图像质量的影响；(3)验证RT剂量计算的改进 精确度。我们将使用台式CBCT系统进行实验，因为它可以灵活地测试各种 ASG原型。最终优化的2D ASG原型将适合安装在临床CBCT系统中 进一步的成像实验或临床试验。本项目成果也可转化为其他CBCT 具有固定源-探测器几何结构的医疗设备

Project Summary Scattered radiation remains a major problem in CBCT imaging that degrades soft tissue visualization and quantitative accuracy. In image guided radiation therapy (IGRT), poor CBCT image quality due to scatter corrupts the accuracy of patient setup corrections and prevents the use of CBCT in radiation therapy (RT) dose calculations and automated tissue segmentations. The latter issue in particular is a major roadblock to enable patient-specific adaptive radiotherapy, whereby the treatment plan is modified during the course of treatment in response to tumor and normal tissue anatomic changes during treatment. To mitigate the scatter problem, software-based scatter correction methods and hardware-based scatter rejection devices, such as radiographic antiscatter grids (ASGs), have been heavily investigated in the past decade. However, the desired improvement in CT number (Hounsfield Unit) accuracy and low contrast sensitivity has not been achieved. Thus, to overcome the shortcomings of current scatter suppression methods, we will develop a novel scatter rejection device, a two dimensional focused antiscatter grid (2D ASG), dedicated for CBCT systems used in IGRT. The scatter suppression advantage of a 2D array over a radiographic ASG, is well known. However, construction of a 2D ASG with favorable primary x-ray transmission properties has not been achievable using standard manufacturing processes. To address this challenge, we will employ a 3D printing technology, to build the 2D ASG from tungsten. By utilizing 3D printing, septal thickness of the 2D ASG will be significantly reduced and each through-hole will be precisely aligned towards the x-ray focal spot. Furthermore, aluminum or fiber inter-septal spacers as in radiographic ASGs will be eliminated due to the mechanical strength of the tungsten 2D array. We hypothesize that the proposed design will enable significant enhancement in soft tissue structure visualization, and it will significantly reduce CT number calculation inaccuracy due to its high primary transmission levels and efficient scatter suppression capability. To test our hypothesis, we will (1) simulate and build 2D ASG prototypes using 3D printing technology, and characterize their signal transmission properties, (2) evaluate the impact of 2D ASG on CBCT image quality, (3) validate improvements in RT dose calculation accuracy. We will perform the experiments using a benchtop CBCT system due to its flexibility to test various ASG prototypes. The final, optimized 2D ASG prototype will be suitable to install in clinical CBCT systems for further imaging experiments or clinical trials. The outcome of this project can also be translated to other CBCT modalities that have fixed source-detector geometry