Yang Ching-Ching, Chen Fong-Lin, Lo Yeh-Chi
Department of Medical Imaging and Radiological Sciences, Tzu-Chi University of Science and Technology, Hualien, Taiwan.
Department of Medical Physics, Koo Foundation Sun Yat-Sen Cancer Center, Taipei City, Taiwan.
PLoS One. 2016 Jun 9;11(6):e0157072. doi: 10.1371/journal.pone.0157072. eCollection 2016.
The aim of this study was to improve the image quality of cone-beam computed tomography (CBCT) mounted on the gantry of a linear accelerator used in radiation therapy based on the image information provided by planning multi-detector CT (MDCT).
MDCT-based shading correction for CBCT and virtual monochromatic CT (VMCT) synthesized using the dual-energy method were performed. In VMCT, the high-energy data were obtained from CBCT, while the low-energy data were obtained from MDCT. An electron density phantom was used to investigate the efficacy of shading correction and VMCT on improving the target detectability, Hounsfield unit (HU) accuracy and variation, which were quantified by calculating the contrast-to-noise ratio (CNR), the percent difference (%Diff) and the standard deviation of the CT numbers for tissue equivalent background material, respectively. Treatment plan studies for a chest phantom were conducted to investigate the effects of image quality improvement on dose planning.
For the electron density phantom, the mean value of CNR was 17.84, 26.78 and 34.31 in CBCT, shading-corrected CBCT and VMCT, respectively. The mean value of %Diff was 152.67%, 11.93% and 7.66% in CBCT, shading-corrected CBCT and VMCT, respectively. The standard deviation within a uniform background of CBCT, shading-corrected CBCT and VMCT was 85, 23 and 15 HU, respectively. With regards to the chest phantom, the monitor unit (MU) difference between the treatment plan calculated using MDCT and those based on CBCT, shading corrected CBCT and VMCT was 6.32%, 1.05% and 0.94%, respectively.
Enhancement of image quality in on-board CBCT can contribute to daily patient setup and adaptive dose delivery, thus enabling higher confidence in patient treatment accuracy in radiation therapy. Based on our results, VMCT has the highest image quality, followed by the shading corrected CBCT and the original CBCT. The research results presented in this study should be able to provide a route to reach a high level of image quality for CBCT imaging in radiation oncology.
本研究的目的是基于计划多排螺旋CT（MDCT）提供的图像信息，提高安装在放射治疗用直线加速器机架上的锥形束计算机断层扫描（CBCT）的图像质量。
对CBCT进行基于MDCT的阴影校正，并使用双能方法合成虚拟单色CT（VMCT）。在VMCT中，高能数据从CBCT获得，而低能数据从MDCT获得。使用电子密度体模研究阴影校正和VMCT对提高目标可检测性、亨氏单位（HU）准确性和变化的效果，分别通过计算对比度噪声比（CNR）、百分比差异（%Diff）和组织等效背景材料CT值的标准差来量化。对胸部体模进行治疗计划研究，以调查图像质量改善对剂量计划的影响。
对于电子密度体模，CBCT、阴影校正后的CBCT和VMCT的CNR平均值分别为17.84、26.78和34.31。CBCT中%Diff的平均值分别为152.67%、阴影校正后的CBCT中为11.93%、VMCT中为7.66%。CBCT、阴影校正后的CBCT和VMCT在均匀背景内的标准差分别为85、23和15 HU。对于胸部体模，使用MDCT计算的治疗计划与基于CBCT、阴影校正后的CBCT和VMCT的治疗计划之间的监测单位（MU）差异分别为6.32%、1.05%和0.94%。
提高机载CBCT的图像质量有助于日常患者摆位和自适应剂量输送，从而在放射治疗中提高对患者治疗准确性的信心。根据我们的结果，VMCT具有最高的图像质量，其次是阴影校正后的CBCT和原始CBCT。本研究中呈现的数据应能够为实现放射肿瘤学中CBCT成像的高水平图像质量提供一条途径。
