Chen Guang-Pei, Tai An, Keiper Timothy D, Lim Sara, Li X Allen
Department of Radiation Oncology, Medical College of Wisconsin, 8701 Watertown Plan Rd, Milwaukee, WI, 53226, USA.
Med Phys. 2020 Jul;47(7):2814-2825. doi: 10.1002/mp.14171. Epub 2020 May 11.
To evaluate the performance of the first clinical real-time motion tracking and compensation system using multileaf collimator (MLC) and jaws during helical tomotherapy delivery.
Appropriate mechanical and dosimetry tests were performed on the first clinical real-time motion tracking system (Synchrony on Radixact, Accuray Inc) recently installed in our institution. kV radiography dose was measured by CTDIw using a pencil chamber. Changes of beam characteristics with jaw offset and MLC leaf shift were evaluated. Various dosimeters and phantoms including A1SL ion chamber (Standard Imaging), Gafchromic EBT3 films (Ashland), TomoPhantom (Med Cal), ArcCheck (Sun Nuclear), Delta4 (ScandiDos), with fiducial or high contrast inserts, placed on two dynamical motion platforms (CIRS dynamic motion-CIRS, Hexamotion-ScandiDos), were used to assess the dosimetric accuracy of the available Synchrony modalities: fiducial tracking with nonrespiratory motion (FNR), fiducial tracking with respiratory modeling (FR), and fiducial free (e.g., lung tumor tracking) with respiratory modeling (FFR). Motion detection accuracy of a tracking target, defined as the difference between the predicted and instructed target positions, was evaluated with the root mean square (RMS). The dose accuracy of motion compensation was evaluated by verifying the dose output constancy and by comparing measured and planned (predicted) three-dimensional (3D) dose distributions based on gamma analysis.
The measured CTDIw for a single radiograph with a 120 kVp and 1.6 mAs protocol was 0.084 mGy, implying a low imaging dose of 8.4 mGy for a typical Synchrony motion tracking fraction with 100 radiographs. The dosimetric effect of the jaw swing or MLC leaf shift was minimal on depth dose (<0.5%) and was <2% on both beam profile width and output for typical motions. The motion detection accuracies, that is, RMS, were 0.84, 1.13, and 0.48 mm for FNR, FR, and FFR, respectively, well within the 1.5 mm recommended tolerance. Dose constancy with Synchrony was found to be within 2%. The gamma passing rates of 3D dose measurements for a variety of Synchrony plans were well within the acceptable level.
The motion tracking and compensation using kV radiography, MLC shifting, and jaw swing during helical tomotherapy delivery was tested to be mechanically and dosimetrically accurate for clinical use.
评估在螺旋断层放射治疗过程中使用多叶准直器（MLC）和光阑的首个临床实时运动跟踪与补偿系统的性能。
对最近安装在我们机构的首个临床实时运动跟踪系统（Radixact上的Synchrony，Accuray公司）进行了适当的机械和剂量学测试。使用铅笔电离室通过CTDIw测量千伏摄影剂量。评估了光阑偏移和MLC叶片移动时射束特性的变化。将各种剂量仪和体模，包括带有基准或高对比度插入物的A1SL电离室（标准影像公司）、Gafchromic EBT3胶片（亚什兰公司）、TomoPhantom（Med Cal）、ArcCheck（太阳核子公司）、Delta4（ScandiDos），放置在两个动态运动平台（CIRS动态运动-CIRS，Hexamotion-ScandiDos）上，用于评估可用的Synchrony模式的剂量学准确性：非呼吸运动的基准跟踪（FNR）、呼吸建模的基准跟踪（FR）以及呼吸建模的无基准（例如肺肿瘤跟踪）（FFR）。跟踪目标的运动检测精度定义为预测目标位置与指令目标位置之间的差异，通过均方根（RMS）进行评估。通过验证剂量输出稳定性并基于伽马分析比较测量的和计划（预测）的三维（3D）剂量分布，评估运动补偿的剂量准确性。
对于采用120 kVp和1.6 mAs协议的单张射线照片，测量得到的CTDIw为0.084 mGy，这意味着对于具有100张射线照片的典型Synchrony运动跟踪分次，成像剂量较低，为8.4 mGy。光阑摆动或MLC叶片移动对深度剂量的剂量学影响极小（<0.5%），对于典型运动，对射束轮廓宽度和输出的影响均<2%。FNR、FR和FFR的运动检测精度（即RMS）分别为0.84、1.13和0.48 mm，完全在推荐的1.5 mm公差范围内。发现Synchrony的剂量稳定性在2%以内。各种Synchrony计划的3D剂量测量的伽马通过率均在可接受水平内。
经测试，在螺旋断层放射治疗过程中使用千伏摄影、MLC移动和光阑摆动进行运动跟踪和补偿在机械和剂量学方面对于临床应用是准确的。
