Evaluation of tumor motion management strategies in radiotherapy using 4D-MRI

描述（由申请人提供）：患者的非自主和自主运动是实现癌症高精度放射治疗的主要障碍，尤其是在胸部和上腹部。由于目标持续移动，因此必须向临床目标体积添加额外的裕度，以补偿由呼吸诱导的器官运动引起的不确定性，从而对正常组织造成不必要的毒性并限制递送到目标的剂量。由于缺乏可靠和安全的直接肿瘤跟踪方法，临床上通常使用替代物来补偿放射治疗期间的肿瘤运动。然而，替代物和肿瘤运动之间的关系不能被概括，因为它取决于个体患者、肿瘤位置和治疗分数。因此，我们的理解之间的相关性的替代和实际的分次内肿瘤运动由于呼吸是非常有限的。虽然4D-CT图像通常用于放射治疗运动评估和规划，但它是单次呼吸周期的过度简化的快照表示，并且固有地受到辐射剂量的限制。因此，这些限制妨碍了在表示治疗会话的时间尺度上获取信息的适用性。动态MRI的进步为治疗前放射治疗提供了机会，但尚未得到系统的利用。MRI是非常有利的，因为它是非电离的，并提供良好的软组织对比度。呼吸运动的变化可以通过在更长的持续时间内或更频繁地成像来捕获。MRI还实现了比4D-CT更快的帧速率，这可能提供对移动解剖结构的更准确描述。在这项研究中，我们将使用动态MRI技术来表征肿瘤运动以及用于预测肿瘤运动的替代物。通过这项研究，我们将充分表征患者特异性呼吸诱导的肿瘤运动，并评估目前在放射治疗中使用的基于替代物的运动管理策略的准确性和有效性。具体而言，在与放射治疗一致的持续时间内获得的4D-MRI将提供肿瘤和替代物的时空信息，因此可以作为评估替代物肿瘤运动跟踪质量的手段，为个体患者提供适当的运动管理策略。所提出的方法将具有普遍适用性的胸部和腹部部位的疾病。我们希望这项研究将成为 如果是这样的话，很可能会导致放射治疗实践的改变，使无数的胸部和腹部癌症患者在未来受益。

DESCRIPTION (provided by applicant): Involuntary and voluntary patient motion is a major obstacle for achieving high-precision radiation therapy of cancers especially in the thorax and upper abdomen. As the target is continuously moving, an additional margin has to be added to the clinical target volume to compensate for the uncertainty caused by the respiration-induced organ motion, causing unnecessary toxicity to the normal tissue and limiting the dose delivered to the target. Due to the lack of reliable and safe direct tumor tracking methods, surrogates are commonly used in clinics to compensate for the tumor motion during radiotherapy. However, the relationship between the surrogate and tumor motion cannot be generalized as it depends on individual patients, tumor location, and treatment fractions. Therefore, our understanding of the correlation between the surrogate and the actual intrafraction tumor motion due to respiration is very limited. Although 4D-CT image is typically used for the radiotherapy motion assessment and planning, it is an oversimplified snapshot representation of a single-breathing cycle and is inherently limited by radiation dose. Consequently, these limitations prevent applicability in acquiring information over timescales that represent a treatment session. Advances in dynamic MRI present opportunities for the pre-treatment radiotherapy setting that have yet to be systematically harnessed. MRI is highly advantageous as it is non-ionizing and provides excellent soft tissue contrast. Variations in respiratory motion can be captured by imaging over longer durations or more frequently. MRI also achieves faster frame rates than 4D-CT, which likely provides a more accurate description of the moving anatomy. In this study, we will use dynamic MRI techniques to characterize tumor motion as well as surrogates used for predicting tumor motion. By way of this research, we will fully characterize patient-specific respiration- induced tumor motion and evaluate the accuracy and effectiveness of surrogate-based motion management strategies currently used in radiotherapy. Specifically, 4D-MRI obtained over a temporal duration consistent with radiotherapy treatments will provide spatio-temporal information of both the tumor and surrogate, and therefore can serve as a means to assess the quality of the tumor motion tracking with the surrogate, suggesting an appropriate motion management strategy for individual patients. The proposed methods will have general applicability to both thoracic and abdominal sites of disease. We intend that this research will be ground breaking and, if so, will likely result in a change of practice in radiotherapy, benefiting innumerable thoracic and abdominal cancer patients in the future.