用于图像引导放射治疗的双能锥束CT的个体化成像方案研究

Compared with single-energy cone beam CT (SECBCT), dual-energy cone beam CT (DECBCT) has improved image quality and increased accuracy of relative electron density, and has the potential for image-guided radiotherapy. Our early research results have demonstrated that personalized imaging protocols based on the correlation between organ dose and patient’s size for SECBCT can be utilized to reduce imaging doses to the patients effectively. However, the scanning protocols of DECBCT are quite different from those of SECBCT, which prevents personalized imaging protocols of SECBCT from being applied to acquire DECBCT with the current hardware system. Hence, the goal of this project is to, based on Monte Carlo simulation, for the first time, develop a set of personalized imaging protocols based on the patient size for DECBCT so that the radiation treatments can be delivered accurately with image-guidance while the secondary cancer risks associated with the imaging doses can be significantly reduced in patients. To start with, the image quality of DECBCT will be analyzed, and ten scanning protocols that can meet the clinical demand with lower radiation dose will be obtained. Then, for the ten scanning protocols, the personalized dose estimation method of DECBCT will be established and verified respectively. Finally, a set of personalized imaging protocols of DECBCT will be established based on conjugate gradient search algorithm in multi-dimensions, and the phantom experiments will be performed to verify the dosimetry and image quality.

和单能锥束CT（CBCT）相比，双能CBCT具有更高的图像质量和更准确的相对电子密度，具有用于图像引导放射治疗的潜力。本组的研究结果表明：基于器官剂量-患者体型大小关系建立的单能CBCT的个体化成像方案，能够有效降低患者的成像剂量。然而，双能CBCT的扫描方案与单能CBCT不同，导致采用现有的硬件系统获取双能CBCT图像时无法应用单能CBCT的个体化成像方案。因此，本项目拟基于蒙特卡洛方法，为双能CBCT首次建立基于患者体型大小的一套个体化成像方案，充分发挥双能CBCT进行图像引导精确放疗的作用，降低患者的成像剂量及其次级癌变风险。首先，分析双能CBCT的图像质量，获取图像质量能够满足临床需求且辐射剂量较低的十个扫描方案。然后，为十个扫描方案分别建立和验证双能CBCT的个体化剂量估算方法。最后基于多维共轭梯度搜索算法建立双能CBCT的个体化成像方案，并开展模体实验进行剂量学和图像质量验证。

双能CBCT的图像质量与相对电子密度准确性高于单能CBCT。双能CBCT的成像剂量与患者体型、成像方案有关，且多次图像引导会给部分病人带来不可忽略的累积成像剂量及其二次致癌风险。如何为双能CBCT开发适用于临床放射治疗的个体化成像方案并估算剂量，以便在现有设备上以低剂量获取满足临床需求的图像质量是本领域亟待解决的关键问题。项目创新性地建立基于患者体型大小的个体化双能CBCT成像方案。分析多个成像方案下双能CBCT的图像质量，获取图像质量能够满足临床需求且辐射剂量较低的成像方案；建立双能CBCT的个体化剂量估算方法与个体化成像方案，并开展模体实验进行剂量学和图像质量验证。本项目基于辐射剂量和多尺度图像质量对于模体大小依赖的模型，提出并评价用于双能CBCT的剂量效率优化的新性能指标，有望在无需设备升级或技术投入的情况下，以低剂量获取满足临床需求的双能CBCT图像，具有临床应用价值。