Wagman Raquel, Yorke Ellen, Ford Eric, Giraud Philippe, Mageras Gikas, Minsky Bruce, Rosenzweig Kenneth
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Int J Radiat Oncol Biol Phys. 2003 Mar 1;55(3):659-68. doi: 10.1016/s0360-3016(02)03941-x.
To determine the clinical impact of the Varian Real-Time Position Monitor (RPM) respiratory gating system for treatment of liver tumors.
Ten patients with liver tumors were selected for evaluation of this passive system, which tracks motion of reflective markers mounted on the abdomen with an infrared-sensitive camera. At simulation, a fluoroscopic movie, breathing trace, and CT scans synchronized at end-expiration (E-E) and end-inspiration were acquired in treatment position using the RPM system. Organs and gross tumor volume were contoured on each CT. Each organ's positional change between two scan sets was quantified by calculation of the center of volume shift and an "index coefficient," defined as the volume common to the two versions of the organ to the volume included in at least one (intersection/union). Treatment dose was determined by use of normal tissue complication probability calculations and dose-volume histograms. Gated portal images were obtained to monitor gating reproducibility with treatment.
Eight patients received 177 treatments with RPM gating. Average superior-to-inferior (SI) diaphragm motion on initial fluoroscopy was reduced from 22.7 mm without gating to 5.1 mm with gating. Comparing end-inspiration to E-E CT scans, average SI movement of the right diaphragm was 11.5 mm vs. 2.2 mm for two E-E CT scans. For all organs, average E-I SI organ motion was 12.8 mm vs. 2.0 mm for E-E studies. Index coefficients were closer to 1.0 for E-E than end-inspiration scans, indicating gating reproducibility. The average SI displacement of diaphragm apex on gated portal images compared with DRR was 2.3 mm. Treatment was prolonged less than 10 minutes with gating. The reproducible decrease in organ motion with gating enabled reduction in gross tumor volume-to-planning target volume margin from 2 to 1 cm. This allowed for calculated dose increases of 7%-27% (median: 21.3%) in 6 patients and enabled treatment in 2.
Gating of radiotherapy for liver tumors enables safe margin reduction on tumor volume, which, in turn, may allow for dose escalation.
确定瓦里安实时位置监测（RPM）呼吸门控系统在肝肿瘤治疗中的临床影响。
选择10例肝肿瘤患者评估这种被动系统，该系统通过红外敏感相机跟踪安装在腹部的反射标记的运动。在模拟时，使用RPM系统在治疗位置采集荧光透视电影、呼吸轨迹以及在呼气末（E-E）和吸气末同步的CT扫描。在每个CT上勾勒出器官和大体肿瘤体积。通过计算体积移位中心和“指数系数”来量化两个扫描集之间每个器官的位置变化，“指数系数”定义为器官两个版本的共同体积与至少一个版本中包含的体积之比（交集/并集）。通过使用正常组织并发症概率计算和剂量体积直方图来确定治疗剂量。获取门控门静脉图像以监测治疗时门控的可重复性。
8例患者接受了177次RPM门控治疗。初始荧光透视时平均上下（SI）膈肌运动从无门控时的22.7毫米减少到有门控时的5.1毫米。比较吸气末与E-E CT扫描，右膈肌的平均SI运动在两次E-E CT扫描时为2.2毫米，而在吸气末与E-E CT扫描比较时为11.5毫米。对于所有器官，E-I平均SI器官运动在E-E研究时为2.0毫米，而在吸气末与E-E CT扫描比较时为12.8毫米。E-E扫描的指数系数比吸气末扫描更接近1.0，表明门控的可重复性。与数字重建放射影像（DRR）相比，门控门静脉图像上膈肌顶点的平均SI位移为2.3毫米。门控使治疗延长不到10分钟。门控时器官运动的可重复性降低使得大体肿瘤体积与计划靶体积的边缘从2厘米减少到1厘米。这使得6例患者的计算剂量增加了7%-27%（中位数：21.3%），并使2例患者能够接受治疗。
肝肿瘤放疗的门控能够安全地缩小肿瘤体积边缘，进而可能允许剂量增加。
