Wang Xin, Ghia Amol J, Zhao Zhongxiang, Yang Jinzhong, Luo Dershan, Briere Tina M, Pino Ramiro, Li Jing, McAleer Mary F, Weksberg David C, Chang Eric L, Brown Paul D, Yang James N
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
J Radiosurg SBRT. 2016;4(3):191-201.
To assess the dosimetric effects of respiratory motion on the target and spinal cord in spinal stereotactic body radiation therapy (SBRT).
Thirty patients with 33 lesions were enrolled on a prospective clinical protocol and simulated with both free-breathing and four-dimensional (4-D) computed tomography (CT). We studied the target motion using 4-D data (10 phases) by registering a secondary image dataset (phase 1 to 9) to a primary image dataset (phase 0) and analyzing the displacement in both translational and rotational directions. The study of dosimetric impacts from respiration includes both the effect of potential target and spinal cord motion and anatomic changes in the beam path. A clinical step-and-shoot IMRT plan generated on the free-breathing CT was copied to the 4-D datasets to evaluate the difference in the dose-volume histogram of target and normal tissues in each phase of a breathing cycle.
Twenty three lesions had no motion in a breathing cycle; four lesions had anterior-posterior motion ≤ 0.2 mm; two lesions had lateral motion ≤ 0.2 mm; and eight lesions had superior-inferior motion, most ≤ 0.2 mm with the worst at 0.6 mm. The difference of maximum dose to 0.01 cm of spinal cord in different phases of a breathing cycle was within 20 cGy in worst case. Target volumes that received the prescription dose (V100) varied little, with deviations of V100 of each phase from the average CT < 1% in most cases. Only when lesions were close to the diaphragm (e.g., at T11) did the V100 deviate by about 7% in the worst case scenario. However, this was caused by a small dose difference of 20 cGy to part of the target volume.
Breathing induced target and spinal cord motion is negligible compared with other setup uncertainties. Dose calculation using averaged or free-breathing CT is reliable when posterior beams are used.
评估在脊柱立体定向体部放射治疗（SBRT）中呼吸运动对靶区和脊髓的剂量学影响。
30例患有33个病灶的患者纳入一项前瞻性临床方案，分别在自由呼吸和四维（4D）计算机断层扫描（CT）下进行模拟。我们通过将一个次级图像数据集（第1至9期）配准到一个初级图像数据集（第0期）并分析平移和旋转方向上的位移，利用4D数据（10个时相）研究靶区运动。呼吸剂量学影响的研究包括潜在靶区和脊髓运动的影响以及射线路径中的解剖结构变化。将基于自由呼吸CT生成的临床步进式调强放疗（IMRT）计划复制到4D数据集中，以评估呼吸周期各时相中靶区和正常组织剂量体积直方图的差异。
23个病灶在呼吸周期中无运动；4个病灶前后向运动≤0.2mm；2个病灶侧向运动≤0.2mm；8个病灶上下向运动，多数≤0.2mm，最差为0.6mm。呼吸周期不同时相中脊髓0.01cm处最大剂量的差异在最坏情况下在20cGy以内。接受处方剂量（V100）的靶区体积变化很小，大多数情况下各时相的V100与平均CT的偏差<1%。仅当病灶靠近膈肌（如T11）时，在最坏情况下V100偏差约7%。然而，这是由靶区部分体积20cGy的小剂量差异引起的。
与其他摆位不确定性相比，呼吸引起的靶区和脊髓运动可忽略不计。当使用后向射野时，使用平均CT或自由呼吸CT进行剂量计算是可靠的。
