Ma Yunzhi, Lee Louis, Keshet O, Keall Paul, Xing Lei
Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California 94305-5847, USA.
Med Phys. 2009 Jun;36(6):2215-21. doi: 10.1118/1.3121425.
The purpose of this study is to develop a 4D inverse planning strategy capable of controlling the appearance of the implanted fiducial(s) in segmented IMRT fields for cine MV or combined MV/kV image-guided IMRT. This work is focused on enhancing the visibility of the implanted fiducial(s) in 4D IMRT inverse planning, whose goal is to derive a set of time-resolved (or phase-tagged) MLC segments to cater for the motion of the patient anatomy extracted from the emerging 4D images. The task is to optimize the shapes and weights of all the segments for each incident beam, with the fiducial(s) being forced/encouraged to be inside the segmented fields. The system is modeled by a quadratic objective function with inclusion of a hard/soft constraint characterizing the authors' level of preference for the fiducial(s) to be included in the segmented fields. A simulated annealing algorithm is employed to optimize the system. The proposed technique is demonstrated using two clinical cases. A segment-based inverse planning framework for 4D radiation therapy, capable of providing tempospatially optimized IMRT plans, has been established. Furthermore, using the described 4D optimization approach, it is demonstrated that the MLC blockage of the implanted fiducial(s) during the segmented delivery is avoided without severely compromising the final dose distribution. The visibility of implanted fiducials in 4D IMRT can be improved without significantly deteriorating final dose distribution. This is a foundation for the authors to use cine MV or combined MV/KV to effectively guide the 4D IMRT delivery.
本研究的目的是开发一种4D逆向计划策略，该策略能够控制在用于动态MV或MV/kV联合图像引导IMRT的分割IMRT射野中植入基准标记的显示效果。这项工作着重于提高4D IMRT逆向计划中植入基准标记的可见性，其目标是得出一组时间分辨（或相位标记）的MLC片段，以适应从新出现的4D图像中提取的患者解剖结构的运动。任务是针对每个入射射束优化所有片段的形状和权重，同时迫使/鼓励基准标记位于分割射野内。该系统由一个二次目标函数建模，其中包含一个硬/软约束，表征作者对于基准标记包含在分割射野中的偏好程度。采用模拟退火算法对系统进行优化。使用两个临床病例演示了所提出的技术。已经建立了一个基于片段的4D放射治疗逆向计划框架，该框架能够提供时空优化的IMRT计划。此外，使用所描述的4D优化方法，证明了在分割照射期间避免了植入基准标记的MLC遮挡，同时又不会严重损害最终剂量分布。在不显著恶化最终剂量分布的情况下，可以提高4D IMRT中植入基准标记的可见性。这是作者使用动态MV或MV/KV联合来有效引导4D IMRT照射的基础。
