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

描述（由申请人提供）：锥形束计算机断层扫描（CBCT）已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过度的成像剂量，特别是当在长达6周的IGRT治疗过程中对患者进行重复扫描时。CBCT每个疗程可向健康器官提供高达100~300 cGy的剂量，增加了继发性癌症或遗传缺陷等生物风险。这对于辐射敏感的患者群体尤其危险，例如儿童患者，对他们来说，CBCT引导的IGRT是被禁止的。因此，尽管CBCT具有巨大的图像引导能力，但其日常使用的好处被过量的X射线剂量抵消了。开发成像剂量大大降低的新型CBCT技术对于满足安全图像引导的临床需求并最大限度地挖掘其在所有临床场景中的潜力至关重要。的一个独特特征 IGRT中的CBCT是在治疗过程中对患者进行重复成像。目前，相同的CBCT方案用于所有部分，并且研究工作致力于减少每个单独扫描的剂量。然而，CBCT图像内容的级分间变化预期较小。利用这种独特的相关性沿着时间维度，原则上可以为IGRT中的CBCT提供进一步的剂量降低，除了那些当前的低剂量技术之外。鉴于这一事实，我们提出了渐进剂量控制（PDC）计划。具体而言，与使用静态扫描协议的当前CBCT实践相反，应用动态调整的协议，其逐渐降低每个部分的成像剂量。CBCT的质量通过将所有先前可用的图像作为先验知识经由基于先验图像的非局部均值（PINLM）方法来保持。增加的先验知识量防止了由于剂量减少而导致的图像质量损失，允许每次逐步减少剂量，并且在整个过程中显著减少总体剂量。多年来，我们为这个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：SA 1。方案优化。我们将1）将先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，以确定最佳的PDC扫描协议。SA 2.方案评价。通过体模研究和患者研究，我们将评估我们的系统，重点是PDC的临床效益和实用性。PDC方案最大限度地利用了IGRT中重复CBCT扫描的独特功能所提供的先验知识。通过有效地结合从传统上忽略的时间维度提取的信息，我们的方法使IGRT具有范式转移和实用的剂量减少方案。临床引入将通过提供安全准确的图像引导使IGRT患者受益匪浅，特别是那些目前基于CBCT的IGRT仅限于的患者。

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.