Riis Hans L, Zimmermann Sune J
Radiofysisk Laboratorium, Odense University Hospital, Odense C, Denmark.
Acta Oncol. 2009;48(2):267-70. doi: 10.1080/02841860802311007.
Cone beam CT is a powerful tool to ensure an optimum patient positioning in radiotherapy. When cone beam CT scan of a patient is acquired, scan data of the patient are compared and evaluated against a reference image set and patient position offset is calculated. Via the linac control system, the patient is moved to correct for position offset and treatment starts. This procedure requires a reliable system for movement of patient. In this work we present a new method to characterize the reproducibility, linearity and accuracy in table positioning. The method applies to all treatment tables used in radiotherapy.
The table characteristics are investigated on our two recent Elekta Synergy Platforms equipped with Precise Table installed in a shallow pit concrete cavity. Remote positioning of the table uses the auto set-up (ASU) feature in the linac control system software Desktop Pro R6.1. The ASU is used clinically to correct for patient positioning offset calculated via cone beam CT (XVI)-software. High precision steel rulers and a USB-microscope has been used to detect the relative table position in vertical, lateral and longitudinal direction. The effect of patient is simulated by applying external load on the iBEAM table top. For each table position an image is exposed of the ruler and display values of actual table position in the linac control system is read out. The table is moved in full range in lateral direction (50 cm) and longitudinal direction (100 cm) while in vertical direction a limited range is used (40 cm).
Our results show a linear relation between linac control system read out and measured position. Effects of imperfect calibration are seen. A reproducibility within a standard deviation of 0.22 mm in lateral and longitudinal directions while within 0.43 mm in vertical direction has been observed. The usage of XVI requires knowledge of the characteristics of remote table positioning. It is our opinion that the method presented meets the requirements in high precision IGRT.
锥形束CT是确保放射治疗中患者最佳定位的有力工具。获取患者的锥形束CT扫描后，将患者的扫描数据与参考图像集进行比较和评估，并计算患者位置偏移。通过直线加速器控制系统，移动患者以校正位置偏移并开始治疗。此过程需要一个可靠的患者移动系统。在这项工作中，我们提出了一种新方法来表征治疗床定位的可重复性、线性和准确性。该方法适用于放射治疗中使用的所有治疗床。
在我们最近安装在浅坑混凝土腔中的两台配备精密治疗床的医科达Synergy平台上研究治疗床特性。治疗床的远程定位使用直线加速器控制系统软件Desktop Pro R6.1中的自动设置（ASU）功能。ASU在临床上用于校正通过锥形束CT（XVI）软件计算出的患者位置偏移。使用高精度钢尺和USB显微镜检测治疗床在垂直、横向和纵向方向上相对位置。通过在iBEAM治疗床台面上施加外部负载来模拟患者的影响。对于每个治疗床位置，曝光一张尺子的图像，并读出直线加速器控制系统中实际治疗床位置的显示值。治疗床在横向（50 cm）和纵向（100 cm）上进行全范围移动，而在垂直方向上使用有限范围（40 cm）。
我们的结果表明直线加速器控制系统读出值与测量位置之间存在线性关系。可以看到校准不完美的影响。在横向和纵向方向上观察到标准偏差在0.22 mm以内的可重复性，而在垂直方向上为0.43 mm以内。使用XVI需要了解远程治疗床定位的特性。我们认为所提出的方法满足高精度图像引导放射治疗的要求。
