4D cone beam CT reconstruction for radiotherapy via motion vector optimization

描述（申请人提供）：肺癌和上腹部肿瘤的治疗采用放射治疗。有明确的证据表明，局部控制率和生存率与高剂量辐射水平有关。保留正常组织对于预防并发症也至关重要，特别是在同时进行化疗和放疗时。因此，肿瘤靶向是非常重要的，这对那些受呼吸器运动影响的部位尤其具有挑战性。多年来，广泛的努力已经致力于开发新的模拟，规划和交付技术，以适应运动。然而，由于计划和治疗阶段之间存在很大的运动变化，这些新的努力由于缺乏高质量的4D图像引导模式而受到损害。特别是在越来越多使用的超分割或立体定向身体放射手术中，高分割剂量使它们对靶向错误的容错性更小。此外，适应性放射治疗（ART）具有补偿剂量传递错误的潜力。这对于肺部和上腹部放射治疗尤其重要，因为呼吸运动和肿瘤缩小。准确评估治疗适应剂量需要高质量的四维锥束CT （4DCBCT）。最近，4DCBCT已经发展到提供呼吸期分辨图像用于治疗指导。由于以下原因，其临床应用受到限制。(1)电流

DESCRIPTION (provided by applicant): Radiotherapy is employed for lung and upper abdominal cancer treatments. There are clear evidences that local control and survival rates are correlated with high radiation dose level. Normal tissue sparing is also critical to prevent complications, especially in concurrent chemo- and radio- therapies. Tumor targeting is hence of significant importance, which is particularly challenging for those sites affected by respirator motions. Over the years, extensive efforts have been devoted to developing novel simulation, planning, and delivery techniques to accommodate motion. Yet, due to large motion variations between planning and treatment sessions, those novel efforts are compromised by the missing of high-quality 4D image-guidance modality. Especially in the increasingly used hyper-fractionation or stereotactic body radio-surgery, the high fractional dose makes them less forgiving to targeting error. Moreover, adaptive radiation therapy (ART) holds the potential to compensate errors in dose delivery. This is particularly important for lung and upper abdominal radiotherapy because of respiratory motion and tumor shrinkage. To accurately evaluate delivered dose for treatment adaptation calls for high-quality 4D cone beam CT (4DCBCT). Recently, 4DCBCT has been developed to provide respiratory-phase resolved images for treatment guidance. Its clinical applications are limited due to the following reasons. (1) Current reconstruction algorithms require long scan protocol. Yet, even under a 4-min scans, the image quality is still inferior to that of a standard 1-min 3D CBCT of static objects, let alone CT. (2) t is susceptible to scatter contamination. Truncation problem further degrades image quality and causes missing anatomy outside the field of view. These deteriorate dose calculations accuracy. One unique feature of radiotherapy is the availability of patient-specific prior information at treatment simulation. We believe that the aforementioned problems can be solved by incorporating the prior information, as well as employing novel reconstruction methods. The overall goal of this proposal is to develop and validate a 4DCBCT reconstruction system that retrieves high-quality 4DCBCT with combined geometry and intensity accuracies under a standard 1-min 3D CBCT scan protocol. Our method reconstructs 4DCBCT via motion vector domain, which is fundamentally different from conventional approaches via image intensity domain. The feasibility of this project has been demonstrated by our preliminary studies. Our goal will be accomplished by pursuing the following specific aims (SAs). SA1. We will develop a complete 4DCBCT reconstruction system. SA2. We will validate our system and demonstrate its clinical advantages. Upon completion, a novel 4DCBCT reconstruction system will have been developed and comprehensively tested. Its clinical advantages will have been demonstrated. Clinical introduction of such a system will lead to immense benefits to lung and upper abdominal cancer patients under IGRT and future ART.