Department of Radiation Oncology, Rush University Medical Center, Chicago, IL, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2020 Aug 10;65(15):155013. doi: 10.1088/1361-6560/ab9355.
By collecting photons scattered out of the therapy beam, scatter imaging creates images of the treated volume. Two phantoms were used to assess the possible application of scatter imaging for markerless tracking of lung tumors during stereotactic body radiation therapy (SBRT) treatment. A scatter-imaging camera was assembled with a CsI flat-panel detector and a 5 mm diameter pinhole collimator. Scatter images were collected during the irradiation of phantoms with megavoltage photons. To assess scatter image quality, spherical phantom lung tumors of 2.1-2.8 cm diameters were placed inside a static, anthropomorphic phantom. To show the efficacy of the technique with a moving target (3 cm diameter), the position of a simulated tumor was tracked in scatter images during sinusoidal motion (15 mm amplitude, 0.25 Hz frequency) in a dynamic lung phantom in open-field, dynamic conformal arc (DCA), and volumetric modulated arc therapy (VMAT) deliveries. Anatomical features are identifiable on static phantom scatter images collected with 10 MU of delivered dose (2.1 cm diameter lung tumor contrast-to-noise ratio of 4.4). The contrast-to-noise ratio increases with tumor size and delivered dose. During dynamic motion, the position of the 3.0 cm diameter lung tumor was identified with a root-mean-square error of 0.8, 1.2, and 2.9 mm for open field (0.3 s frame integration), DCA (0.5 s), and VMAT (0.5 s), respectively. Based on phantom studies, scatter imaging is a potential technique for markerless lung tumor tracking during SBRT without additional imaging dose. Quality scatter images may be collected at low, clinically relevant doses (10 MU). Scatter images are capable of sub-millimeter tracking precision, but modulation decreases accuracy.
通过收集从治疗束散射出的光子，散射成像是创建受治疗体积的图像。使用两个体模来评估散射成像在立体定向体部放射治疗（SBRT）期间对无标记跟踪肺肿瘤的潜在应用。组装了一个带有 CsI 平板探测器和 5mm 直径针孔准直器的散射成像相机。在照射体模的过程中收集散射图像。为了评估散射图像质量，将直径为 2.1-2.8cm 的球形体模肺肿瘤放置在静态、拟人化体模内。为了展示该技术对运动目标的有效性（直径 3cm），在开放场、动态适形弧（DCA）和容积调制弧治疗（VMAT）中，在动态肺体模中模拟肿瘤的位置在散射图像中跟踪正弦运动（幅度 15mm，频率 0.25Hz）。在使用 10MU 剂量（直径 2.1cm 的肺肿瘤对比度噪声比为 4.4）的静态体模散射图像上可识别出解剖特征。对比度噪声比随肿瘤大小和剂量增加而增加。在动态运动期间，3.0cm 直径肺肿瘤的位置通过开放场（0.3s 帧积分）、DCA（0.5s）和 VMAT（0.5s）的均方根误差分别为 0.8、1.2 和 2.9mm 确定。基于体模研究，散射成像技术是一种在 SBRT 期间对无标记肺肿瘤进行跟踪的潜在技术，无需额外的成像剂量。质量散射图像可能在低剂量（10MU）下收集。散射图像能够实现亚毫米级跟踪精度，但调制会降低精度。
