Daily quality assurance phantom for ultrasound image guided radiation therapy

A simple phantom was designed, constructed, tested, and clinically implemented for daily quality assurance ( QA) of an ultrasound-image-guided radiation therapy ( US-IGRT) system, the Restitu Ultrasound system ( Resonant Medical, Montreal, QC). The phantom consists of a high signal echogenic background gel surrounding a low signal hypoechoic egg-shaped target. Daily QA checks involve ultrasound imaging of the phantom and segmenting of the embedded target using the automated tools available on the US-IGRT system. This process serves to confirm system hardware and software functions and, in particular, accurate determination of the target position. Experiments were conducted to test the stability of the phantom at room temperature, its tissue-mimicking properties, the reproducibility of target position measurements, and the usefulness of the phantom as a daily QA device. The phantom proved stable at room temperature, exhibited no evidence of bacterial or fungal invasion in 9 months, and showed limited desiccation ( resulting in a monthly reduction in ultrasound-measured volume of approximately 0.2 cm(3)). Furthermore, the phantom was shown to be nearly tissue-mimicking, with speed of sound in the phantom estimated to be 0.8% higher than that assumed by the scanner calibration. The phantom performs well in a clinical setting, owing to its light weight and ease of operation. It provides reproducible measures of target position even with multiple users. At our center, the phantom is being used for daily QA of the US-IGRT system with clinically acceptable tolerances of +/- 1 cm(3) on target volume and +/- 2 mm on target position. For routine daily QA, this phantom is a good alternative to the manufacturer-supplied calibration phantom, and we recommended that that larger phantom be reserved for less frequent, more detailed QA checks and system calibration.

设计、构建、测试了一种简易体模，并将其应用于临床，用于超声图像引导放射治疗（US - IGRT）系统（瑞思图超声系统，Resonant Medical公司，加拿大魁北克省蒙特利尔市）的日常质量保证（QA）。该体模由高信号回声背景凝胶组成，凝胶内包围着一个低信号弱回声的蛋形靶区。日常QA检查包括对体模进行超声成像，并使用US - IGRT系统上的自动化工具对嵌入的靶区进行分割。这一过程用于确认系统硬件和软件功能，特别是对靶区位置的准确测定。进行了实验以测试体模在室温下的稳定性、其仿组织特性、靶区位置测量的可重复性以及该体模作为日常QA设备的实用性。体模在室温下稳定，在9个月内未出现细菌或真菌侵入的迹象，并且干燥程度有限（导致超声测量体积每月减少约0.2立方厘米）。此外，体模被证明几乎具有仿组织特性，体模中的声速估计比扫描仪校准所采用的声速高0.8%。由于其重量轻且操作简便，该体模在临床环境中表现良好。即使由多个使用者操作，它也能提供可重复的靶区位置测量结果。在我们中心，该体模正用于US - IGRT系统的日常QA，靶区体积的临床可接受公差为±1立方厘米，靶区位置为±2毫米。对于常规的日常QA，这种体模是制造商提供的校准体模的良好替代品，我们建议将较大的体模保留用于不太频繁但更详细的QA检查和系统校准。