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

描述(由申请人提供)：非自愿和自愿的患者活动是实现高精度癌症放射治疗的主要障碍，特别是在胸部和上腹部。由于靶点不断移动，临床靶点体积必须增加额外的余量，以补偿呼吸诱导的器官运动所造成的不确定性，从而对正常组织造成不必要的毒性，并限制向靶点输送的剂量。由于缺乏可靠、安全的直接肿瘤示踪方法，临床上常采用替代物来补偿放射治疗过程中肿瘤的运动。然而，代理与肿瘤运动之间的关系不能一概而论，因为它取决于个体患者、肿瘤位置和治疗比例。因此，我们对代用肿瘤与呼吸引起的实际肿瘤运动之间的相关性的了解非常有限。虽然4D-CT图像通常用于放射治疗的运动评估和规划，但它是对单个呼吸周期的过于简化的快照表示，并且固有地受到辐射剂量的限制。因此，这些限制阻碍了在代表治疗过程的时间尺度上获取信息的适用性。动态磁共振成像的进展为治疗前放射治疗提供了机会，但尚未得到系统的利用。磁共振成像是非常有利的，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成像在更长的持续时间或更频繁地捕捉到。MRI的帧速率也比4D-CT更快，这可能提供了对运动解剖更准确的描述。在这项研究中，我们将使用动态MRI技术来表征肿瘤的运动以及用于预测肿瘤运动的替代物。通过这项研究，我们将充分描述患者特定的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代理的运动管理策略的准确性和有效性。具体地说，在与放射治疗一致的时间段内获得的4D-MRI将提供肿瘤和替代物的时空信息，因此可以作为一种手段来评估使用替代物跟踪肿瘤运动的质量，为个体患者提供适当的运动管理策略。建议的方法将普遍适用于胸部和腹部的疾病部位。我们打算这项研究将是 开创性的，如果是这样的话，可能会导致放射治疗实践的改变，使未来无数的胸腹癌患者受益。

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.