Integrated radiotherapy imaging system (IRIS): design considerations of tumour tracking with linac gantry-mounted diagnostic x-ray systems with flat-panel detectors
Integrated radiotherapy imaging system (IRIS): design considerations of tumour tracking with linac gantry-mounted diagnostic x-ray systems with flat-panel detectors
复制标题
DOI：
10.1088/0031-9155/49/2/005
复制
发表时间：
2004-01-21
影响因子：
3.5
通讯作者：
Shirato, H
中科院分区：
文献类型：
--
作者：
Berbeco, RI;Jiang, SB;Shirato, H
本文研究了一种由机架式诊断X射线管和快速读出平板非晶硅探测器组成的综合放射治疗成像系统的设计。该系统具有三个主要功能：用于三维（3D）患者设置的X射线照片，锥形束CT和实时肿瘤/标记物跟踪。当前研究的目标是确定一个源/面板对是否足以进行实时肿瘤/标记物跟踪，如果需要两个，则确定每个源/面板相对于其他组件和等中心的最佳位置。安装在机架上的单个源/成像器对当然能够实现上面列出的三个功能中的前两个，并且如果与目标轨迹的先验知识相结合，则也可以用于第三个功能。这将是必要的，因为用单个成像器/源系统只能看到二维运动。然而，利用先前收集的有关轨迹的信息，可以从其他两个坐标中推导出第三个坐标，其精确度足以促进跟踪。只有当3D肿瘤/标记物轨迹从一个部分到另一个部分是一致的时，才能进行第三坐标的这种推导。在这里，使用来自多个治疗部分的7名患者的测量的肺标记物轨迹数据，从理论上研究了使用一个源/成像器对进行肿瘤跟踪的可行性。患者的选择标准包括肿瘤运动的最小平均振幅大于1 cm峰-峰。使用第一部分数据对每例患者的标记物轨迹进行建模。然后，对于其余的数据，标记位置从成像仪在不同机架角度的投影中导出，并与测量的肿瘤位置进行比较。我们的研究结果表明，由于肿瘤运动的三维性和不规则的轨迹特征，在分数到分数的基础上，一个“单视场”系统（单源/成像器）是不够的一致的实时肿瘤跟踪，即使有先验知识。我们发现，在研究的7例患者中，峰-峰标记运动大于1 cm，5例平均定位误差大于2 mm，2例平均误差大于3 mm。由于这种不确定性与单视场系统相关，因此需要两个源/成像仪对进行稳健的3D目标定位。IRIS选择安装在直线加速器机架上的双正交X射线源/成像仪对。我们根据Varian 21 EX Clinac的几何规格进一步研究了X射线源/面板的放置。最佳配置最大限度地减少了定位误差，同时保持大视野，并避免与地板/天花板或治疗床碰撞。
The design of an integrated radiotherapy imaging system (IRIS), consisting of gantry mounted diagnostic (kV) x-ray tubes and fast read-out flat-panel amorphous-silicon detectors, has been studied. The system is meant to be capable of three main functions: radiographs for three-dimensional (3D) patient set-up, cone-beam CT and real-time tumour/marker tracking. The goal of the current study is to determine whether one source/panel pair is sufficient for real-time tumour/marker tracking and, if two are needed, the optimal position of each relative to other components and the isocentre. A single gantry-mounted source/imager pair is certainly capable of the first two of the three functions listed above and may also be useful for the third, if combined with prior knowledge of the target's trajectory. This would be necessary because only motion in two dimensions is visible with a single imager/source system. However, with previously collected information about the trajectory, the third coordinate may be derived from the other two with sufficient accuracy to facilitate tracking. This deduction of the third coordinate can only be made if the 3D tumour/marker trajectory is consistent from fraction to fraction. The feasibility of tumour tracking with one source/imager pair has been theoretically examined here using measured lung marker trajectory data for seven patients from multiple treatment fractions. The patients' selection criteria include minimum mean amplitudes of the tumour motions greater than 1 cm peak-to-peak. The marker trajectory for each patient was modelled using the first fraction data. Then for the rest of the data, marker positions were derived from the imager projections at various gantry angles and compared with the measured tumour positions. Our results show that, due to the three dimensionality and irregular trajectory characteristics of tumour motion, on a fraction-to-fraction basis, a 'monoscopic' system (single source/imager) is inadequate for consistent real-time tumour tracking, even with prior knowledge. We found that, among the seven patients studied with peak-to-peak marker motion greater than 1 cm, five cases have mean localization errors greater than 2 mm and two have mean errors greater than 3 mm. Because of this uncertainty associated with a monoscopic system, two source/imager pairs are necessary for robust 3D target localization. Dual orthogonal x-ray source/imager pairs mounted on the linac gantry are chosen for the IRIS. We further studied the placement of the x-ray sources/panel based on the geometric specifications of the Varian 21EX Clinac. The best configuration minimizes the localization error while maintaining a large field of view and avoiding collisions with the floor/ceiling or couch.