Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109, USA.
Med Phys. 2011 May;38(5):2639-50. doi: 10.1118/1.3578927.
To develop a novel four-dimensional (4D) intensity modulated radiation therapy (IMRT) treatment planning methodology based on dynamic virtual patient models.
The 4D model-based planning (4DMP) is a predictive tracking method which consists of two main steps: (1) predicting the 3D deformable motion of the target and critical structures as a function of time during treatment delivery; (2) adjusting the delivery beam apertures formed by the dynamic multi-leaf collimators (DMLC) to account for the motion. The key feature of 4DMP is the application of a dynamic virtual patient model in motion prediction, treatment beam adjustment, and dose calculation. A lung case was chosen to demonstrate the feasibility of the 4DMP. For the lung case, a dynamic virtual patient model (4D model) was first developed based on the patient's 4DCT images. The 4D model was capable of simulating respiratory motion of different patterns. A model-based registration method was then applied to convert the 4D model into a set of deformation maps and 4DCT images for dosimetric purposes. Based on the 4D model, 4DMP treatment plans with different respiratory motion scenarios were developed. The quality of 4DMP plans was then compared with two other commonly used 4D planning methods: maximum intensity projection (MIP) and planning on individual phases (IP).
Under regular periodic motion, 4DMP offered similar target coverage as MIP with much better normal tissue sparing. At breathing amplitude of 2 cm, the lung V20 was 23.9% for a MIP plan and 16.7% for a 4DMP plan. The plan quality was comparable between 4DMP and IP: PTV V97 was 93.8% for the IP plan and 93.6% for the 4DMP plan. Lung V20 of the 4DMP plan was 2.1% lower than that of the IP plan and Dmax to cord was 2.2 Gy higher. Under a real time irregular breathing pattern, 4DMP had the best plan quality. PTV V97 was 90.4% for a MIP plan, 88.6% for an IP plan and 94.1% for a 4DMP plan. Lung V20 was 20.1% for the MIP plan, 17.8% for the IP plan and 17.5% for the 4DMP plan. The deliverability of the real time 4DMP plan was proved by calculating the maximum leaf speed of the DMLC.
The 4D model-based planning, which applies dynamic virtual patient models in IMRT treatment planning, can account for the real time deformable motion of the tumor under different breathing conditions. Under regular motion, the quality of 4DMP plans was comparable with IP and superior to MIP. Under realistic motion in which breathing amplitude and period change, 4DMP gave the best plan quality of the three 4D treatment planning techniques.
开发一种基于动态虚拟患者模型的新型四维（4D）强度调制放射治疗（IMRT）治疗计划方法。
基于四维模型的计划（4DMP）是一种预测性跟踪方法，主要包括两个步骤：（1）在治疗过程中预测目标和关键结构的三维可变形运动；（2）调整由动态多叶准直器（DMLC）形成的治疗束孔径，以适应运动。4DMP 的关键特征是在运动预测、治疗束调整和剂量计算中应用动态虚拟患者模型。选择一个肺部病例来演示 4DMP 的可行性。对于肺部病例，首先基于患者的 4DCT 图像开发一个动态虚拟患者模型（4D 模型）。4D 模型能够模拟不同模式的呼吸运动。然后应用基于模型的配准方法将 4D 模型转换为一组变形图和用于剂量计算的 4DCT 图像。基于 4D 模型，开发了具有不同呼吸运动场景的 4DMP 治疗计划。然后比较了 4DMP 计划与另外两种常用的 4D 计划方法：最大强度投影（MIP）和个体相位（IP）计划的质量。
在规则周期性运动下，4DMP 提供了与 MIP 相似的靶区覆盖，同时更好地保护了正常组织。在呼吸幅度为 2cm 时，MIP 计划的肺 V20 为 23.9%，4DMP 计划为 16.7%。4DMP 与 IP 之间的计划质量相当：IP 计划的 PTV V97 为 93.8%，4DMP 计划为 93.6%。4DMP 计划的肺 V20 比 IP 计划低 2.1%，脊髓最大剂量高 2.2Gy。在实时不规则呼吸模式下，4DMP 具有最佳的计划质量。MIP 计划的 PTV V97 为 90.4%，IP 计划为 88.6%，4DMP 计划为 94.1%。MIP 计划的肺 V20 为 20.1%，IP 计划为 17.8%，4DMP 计划为 17.5%。通过计算 DMLC 的最大叶片速度，证明了实时 4DMP 计划的可实现性。
基于四维模型的计划将动态虚拟患者模型应用于 IMRT 治疗计划中，可以在不同呼吸条件下计算肿瘤的实时可变形运动。在规则运动下，4DMP 计划的质量与 IP 相当，优于 MIP。在呼吸幅度和周期变化的现实运动中，4DMP 给出了三种 4D 治疗计划技术中最好的计划质量。
