A progressive cone-beam CT dose control scheme for image-guided radiation therapy

描述(申请人提供)：锥形束计算机断层扫描(CBCT)已被常规用于图像引导放射治疗(IGRT)，以提供精确的治疗指导。阻碍其广泛应用的一个主要问题是成像剂量过大，特别是在长达6周的IGRT治疗过程中对患者进行重复扫描时。CBCT每个疗程向健康器官提供高达100~300cGy射线，增加了继发性癌症或遗传缺陷等生物风险。这对辐射敏感的患者群体尤其危险，例如禁止CBCT引导的IGRT的儿科患者。因此，尽管CBCT具有强大的图像引导能力，但其日常使用的好处却被过高的X射线剂量抵消了。开发大大减少成像剂量的新型CBCT技术对于满足临床对安全图像引导的需求以及最大限度地开发其在所有临床场景中的潜力是至关重要的。的一个独特功能 IGRT中的CBCT是指患者在一个治疗过程中重复成像。目前，所有部分都使用相同的CBCT方案，并致力于研究努力减少每一次单独扫描的剂量。然而，CBCT图像内容的分数间差异预计很小。在时间维度上利用这种独特的相关性，原则上可以在现有的低剂量技术之外，为IGRT中的CBCT提供进一步的剂量减少。鉴于这一事实，我们提出了一个渐进剂量控制(PDC)方案。具体地说，与目前使用静态扫描方案的CBCT实践相反，应用了动态调整的方案，该方案逐渐减少了每个部分的成像剂量。通过基于先验图像的非局部均值(PINLM)方法将所有先前可用的图像合并为先验知识来保持CBCT质量。先验知识的增加防止了由于剂量减少而造成的图像质量损失，允许每次逐步减少剂量，并在整个过程中显著地总体减少。多年来，我们为这一项目积累了必要的专业知识。我们将通过追求以下具体目标(SA)来实现我们的目标：SA1。协议优化。我们将1)将以前开发的各种组件集成到一个完整的系统中，2)进行蒙特卡罗模拟研究，以确定最优的PDC扫描协议。SA2.协议评估。通过模体研究和患者研究，我们将评估我们的系统，重点是PDC的临床益处和实用性。PDC方案最大限度地利用IGRT中重复CBCT扫描的独特功能提供的先验知识。通过有效地结合从传统上省略的时间维度提取的信息，我们的方法使IGRT具有范例转换和实用的剂量减少方案。临床引入将为接受IGRT的患者提供安全和准确的影像指导，特别是那些目前仅限于基于CBCT的IGRT的患者，从而极大地使患者受益。

DESCRIPTION (provided by applicant): Cone beam computed tomography (CBCT) has been routinely used in image-guided radiation therapy (IGRT) for precise treatment guidance. One major concern that hinders its wide applications is the excessive imaging dose, especially when repeated scans are performed on a patient over a long IGRT treatment course up to 6 weeks. CBCT delivers up to 100~300 cGy per treatment course to healthy organs, elevating biologic risks such as secondary cancer or genetic defects. This is particularly risky for radiation sensitive patient groups, e.g. pediatric patients, for whom CBCT-guided IGRT is prohibited. Therefore, despite the tremendous image guidance capability of CBCT, the benefits of its daily use are counteracted by excessive x-ray dose. Developing novel CBCT technologies with much reduced imaging dose is critically necessary to address the clinical demands of safe image guidance and to maximally exploiting its potential in all clinical scenarios. One unique feature of CBCT in IGRT is that a patient is repeatedly imaged in a treatment course. Currently, the same CBCT protocol is used for all fractions, and research efforts are devoted to reduce dose to each individual scan. Yet, the inter-fraction variation of CBCT image contents is expected to be small. Exploiting this unique correlation along the temporal dimension can in principle offer a further dose reduction for CBCTs in IGRT, in addition to those current low-dose techniques. In light of this fact, we propose a Progressive Dose Control (PDC) scheme. Specifically, as opposed to the current CBCT practice using a static scan protocol, a dynamically adjusted protocol is applied, which gradually reduce the imaging dose at each fraction. The CBCT quality is maintained by incorporating all previously available images as prior knowledge via a Prior Image- based Non-Local Means (PINLM) method. The increased amount of prior knowledge prevents the loss of image quality due to dose reduction, allowing for a progressive dose reduction each time, and a significant overall reduction over the entire course. Over the years, we have accumulated necessary expertise for this project. We will accomplish our goal by pursuing the following specific aims (SAs): SA1. Protocol Optimization. We will 1) integrate various components previously developed into a whole system, and 2) perform Monte Carlo simulation studies to determine the optimal PDC scan protocol. SA2. Protocol Evaluation. Through both phantom studies and patient studies, we will evaluate our system with emphases on the clinical benefits and practicality of PDC. The PDC scheme maximally utilizes prior knowledge offered by the unique feature of repeated CBCT scans in IGRT. By effectively incorporating information extracted from the conventionally omitted temporal dimension, our approach empowers IGRT with a paradigm-shifting and practical dose reduction scheme. Clinical introduction will benefit patients under IGRT enormously by providing safe and accurate image guidance, especially those patients to whom CBCT-based IGRT is currently limited.