■在这项研究中,对电子射野成像设备(EPID)的成像性能进行了评估。使用QC-3V图像质量模型进行评估。
■6MVLINAC的EPID系统,用于获得QC-3VEPID体模的图像。X射线源到体模的距离为100cm,场尺寸为15X15cm2。对于2MU-100MU范围,照射条件包括200、400和600的剂量速率(DR)。对比度传递函数(CTF)噪声功率谱(NPS),研究了归一化噪声功率谱(NNPS)和对比噪声比(CNR)。此外,显示与频率相关的输出信噪比(SNR)的替代因素,信噪比频率响应(SNFR),已经介绍了。SNFR是一个综合质量指标,在临床环境中容易确定。
■发现CTF曲线彼此相当。在2MU和200MU/min下测量最低值。关于NPS和NNPS图,发现这些值减小到大约0.3lp/mm,并且之后表现出白噪声形状。发现SNFR值随着空间频率而降低。在体模的区域7和11之间发现了最高的CNR。
■研究了MU和DR对EPID性能的影响。使用QC-3V体模评估图像质量。提出的结果可以改善图像质量,并支持当前的图像质量控制常规协议。
UNASSIGNED: In this study an evaluation of the imaging performance of an electronic portal imaging device (EPID) is presented. The evaluation performed employing the QC-3V image quality phantom.
UNASSIGNED: An EPID system of a 6 MV LINAC, was used to obtain images of a QC-3V EPID phantom. The X-ray source to phantom distance was 100 cm and the field size was 15x15 cm2. The irradiation conditions comprised Dose Rates (DR) of 200, 400 and 600 for a 2 MU-100 MU range. The Contrast Transfer Function (CTF), the Noise Power Spectrum (NPS), the Normalized Noise Power Spectrum (NNPS) and the Contrast-to-Noise Ratio (CNR) were studied. In addition, an alternative factor showing a frequency related output signal-to-noise ratio (SNR), the Signal-to-Noise-Frequency Response (SNFR), has been introduced. SNFR is a comprehensive quality index, easily determined in clinical environment.
UNASSIGNED: The CTF curves were found comparable to each other. The lowest values were measured at 2 MU and 200 MU/min. Concerning the NPS and NNPS graphs it was found that the values decrease up to approximately 0.3 lp/mm and demonstrate a white noise shape afterwards. SNFR values were found reducing with spatial frequency. Highest CNR were found between the region 7 and 11 of the phantom.
UNASSIGNED: The influence of MU and DR on EPID performance were investigated. Image quality was assessed using the QC-3V phantom. The presented results can lead to image quality amelioration and act supportively to current image quality control routine protocols.