Department of Radiation Oncology, Brigham and Women's Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA, United States of America.
BioMedical Physics in Radiation Oncology, DKFZ, Heidelberg, Germany.
Phys Med Biol. 2021 Jul 20;66(15). doi: 10.1088/1361-6560/ac1246.
Electronic portal image devices (EPIDs) have been investigated previously for beams-eye view (BEV) applications such as tumor tracking but are limited by low contrast-to-noise ratio and detective quantum efficiency. A novel multilayer imager (MLI), consisting of four stacked flat-panels was used to measure improvements in fiducial tracking during liver stereotactic body radiation therapy (SBRT) procedures compared to a single layer EPID.The prototype MLI was installed on a clinical TrueBeam linac in place of the conventional DMI single-layer EPID. The panel was extended during volumetric modulated arc therapy SBRT treatments in order to passively acquire data during therapy. Images were acquired for six patients receiving SBRT to liver metastases over two fractions each, one with the MLI using all 4 layers and one with the MLI using the top layer only, representing a standard EPID. The acquired frames were processed by a previously published tracking algorithm modified to identify implanted radiopaque fiducials. Truth data was determined using respiratory traces combined with partial manual tracking. Results for 4- and 1-layer mode were compared against truth data for tracking accuracy and efficiency. Tracking and noise improvements as a function of gantry angle were determined.. Tracking efficiency with 4-layers improved to 82.8% versus 58.4% for the 1-layer mode, a relative improvement of 41.7%. Fiducial tracking with 1-layer returned a root mean square error (RMSE) of 2.1 mm compared to 4-layer RMSE of 1.5 mm, a statistically significant ( < 0.001) improvement of 0.6 mm. The reduction in noise correlated with an increase in successfully tracked frames ( = 0.913) and with increased tracking accuracy (0.927).. Increases in MV photon detection efficiency by utilization of a MLI results in improved fiducial tracking for liver SBRT treatments. Future clinical applications utilizing BEV imaging may be enhanced by including similar noise reduction strategies.
电子射野影像装置（EPID）此前已被用于光束眼视图（BEV）应用，例如肿瘤跟踪，但由于对比度噪声比和探测量子效率低而受到限制。一种新型的多层成像仪（MLI），由四个堆叠的平板组成，用于测量与单层 EPID 相比，在肝脏立体定向体部放射治疗（SBRT）过程中对基准跟踪的改进。原型 MLI 安装在临床 TrueBeam 直线加速器上，取代了传统的 DMI 单层 EPID。在容积调强弧形治疗 SBRT 治疗期间，将面板延伸，以便在治疗期间被动地获取数据。对 6 名接受 SBRT 治疗肝转移的患者进行了研究，每位患者接受两次 SBRT 治疗，一次使用 4 层 MLI，一次使用仅顶层的 MLI，代表标准 EPID。使用先前发表的跟踪算法对采集的图像进行处理，该算法经过修改可识别植入的不透射线基准。使用呼吸轨迹和部分手动跟踪来确定真实数据。比较了 4 层和 1 层模式的跟踪准确性和效率。确定了随旋转架角度变化的跟踪和噪声改善情况。4 层模式的跟踪效率提高到 82.8％，而 1 层模式的跟踪效率提高到 58.4％，相对提高了 41.7％。使用 1 层模式返回的基准跟踪均方根误差（RMSE）为 2.1mm，而使用 4 层模式返回的 RMSE 为 1.5mm，相差 0.6mm，具有统计学意义（<0.001）。噪声的减少与成功跟踪帧数的增加（r=0.913）和跟踪精度的提高（0.927）相关。利用 MLI 增加 MV 光子探测效率可提高肝脏 SBRT 治疗的基准跟踪精度。未来利用 BEV 成像的临床应用可能会通过包括类似的降噪策略而得到增强。
