Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota, USA.
Med Phys. 2022 May;49(5):3041-3052. doi: 10.1002/mp.15634. Epub 2022 Mar 30.
Mobile lung tumors are increasingly being treated with ablative radiotherapy, for which precise motion management is essential. In-room stereoscopic radiography systems are able to guide ablative radiotherapy for stationary cranial lesions but not optimally for lung tumors unless fiducial markers are inserted. We propose augmenting stereoscopic radiographic systems with multiple small x-ray sources to provide the capability of imaging with stereoscopic, single frame tomosynthesis.
In single frame tomosynthesis, nine x-ray sources are placed in a 3 × 3 configuration and energized simultaneously. The beams from these sources are collimated so that they converge on the tumor and then diverge to illuminate nine non-overlapping sectors on the detector. These nine sector images are averaged together and filtered to create the tomosynthesis effect. Single frame tomosynthesis is intended to be an alternative imaging mode for existing stereoscopic systems with a field of view that is three times smaller and a temporal resolution equal to the frame rate of the detector. We simulated stereoscopic tomosynthesis and radiography using Monte Carlo techniques on 60 patients with early-stage lung cancer from the NSCLC-Radiomics dataset. Two board-certified radiation oncologists reviewed these simulated images and rated them on a 4-point scale (1: tumor not visible; 2: tumor visible but inadequate for motion management; 3: tumor visible and adequate for motion management; 4: tumor visibility excellent). Each tumor was independently presented four times (two viewing angles from radiography and two viewing angles from tomosynthesis) in a blinded fashion over two reading sessions.
The fraction of tumors that were rated as adequate or excellent for motion management (scores 3 or 4) from at least one viewing angle was 53% using radiography and 90% using tomosynthesis. From both viewing angles, the corresponding fractions were 7% for radiography and 48% for tomosynthesis. Readers agreed exactly on 62% of images and within 1 point on 98% of images. The acquisition technique was estimated to be 75 mAs at 120 kVp per treatment fraction assuming one verification image per breath, approximately one order of magnitude less than a standard dose cone beam CT.
Stereoscopic tomosynthesis may provide a noninvasive, low dose, intrafraction motion verification technique for lung tumors treated by ablative radiotherapy. The system architecture is compatible with real-time video capture at 30 frames per second. Simulations suggest that most, but not all, lung tumors can be adequately visualized from at least one viewing angle.
越来越多的移动肺部肿瘤采用消融放射治疗,这需要精确的运动管理。室内立体放射摄影系统能够为固定的颅病变引导消融放射治疗,但对于肺部肿瘤则不然,除非插入基准标记物。我们建议用多个小 X 射线源增强立体放射摄影系统,以提供具有立体、单次断层合成术的成像能力。
在单次断层合成术中,将九个 X 射线源放置在 3×3 配置中并同时通电。从这些源发出的光束被准直,以使它们汇聚在肿瘤上,然后发散以照亮探测器上的九个非重叠扇形区。将这九个扇形区图像平均并滤波以创建断层合成效果。单次断层合成术旨在成为具有三倍小视野和与探测器帧率相等的时间分辨率的现有立体系统的替代成像模式。我们使用 Monte Carlo 技术对来自 NSCLC-Radiomics 数据集的 60 例早期肺癌患者进行了立体断层合成术和放射摄影模拟。两位经过董事会认证的放射肿瘤学家对这些模拟图像进行了评估,并根据 4 分制(1:肿瘤不可见;2:肿瘤可见但不适合运动管理;3:肿瘤可见且适合运动管理;4:肿瘤可见极好)进行评分。每个肿瘤在两次阅读会议中以盲法独立呈现四次(两次从放射摄影获得的视角和两次从断层合成术获得的视角)。
使用放射摄影术,至少一个视角下可用于运动管理的肿瘤评分(3 或 4 分)的肿瘤比例为 53%,而使用断层合成术则为 90%。从两个视角来看,对应的分数分别为放射摄影术的 7%和断层合成术的 48%。读者对 62%的图像完全一致,对 98%的图像相差 1 分。假设每次呼吸验证一次图像,那么每次治疗的采集技术估计为 120 kVp 时的 75 mAs,大约比标准剂量锥形束 CT 低一个数量级。
立体断层合成术可为消融放射治疗的肺部肿瘤提供一种非侵入性、低剂量、分次内运动验证技术。该系统架构与每秒 30 帧的实时视频捕获兼容。模拟表明,虽然不是所有,但大多数肺部肿瘤都可以从至少一个视角进行充分可视化。