Long-term constancy analysis of image uniformity and noise of cone-beam CT for the OBI system
10.3760/cma.j.cn113030-20230830-00079
- VernacularTitle:OBI系统锥形束CT图像均匀性和噪声的长期稳定性分析
- Author:
Feiyue SHI
1
;
Long CHENG
;
Min WANG
;
Wei QIN
;
Hang QIN
;
Xiaowei WEI
Author Information
1. 南京医科大学附属南京医院（南京市第一医院）肿瘤放疗中心，南京 210006
- Keywords:
Cone-beam computed tomography;
Image uniformity;
Noise;
Long-term constancy
- From:
Chinese Journal of Radiation Oncology
2024;33(9):845-852
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To evaluate the long-term constancy of image uniformity and noise of cone-beam computed tomography (CBCT) for the on-board imager (OBI) system of a Varian linac.Methods:Monthly quality assurance (QA) tests were carried out for the OBI system of a Clinac iX linac, and CBCT images of Catphan 504 phantom were obtained with six scanning protocols. The 6 protocols were high-quality head (HQH), low-dose head (LDH), pelvis spot light (PSL), standard-dose head (SDH), low-dose thorax (LDT) and pelvis, respectively. The 144 series of CBCT images acquired from Nanjing First Hospital, Nanjing Medical University between January 2020 and December 2021 were analyzed, and the data of image uniformity and noise were obtained by delineating regions of interest (ROI) in the images of CTP486 module. Image uniformity was expressed by the absolute value of the maximum difference between the average CT value of the ROI in the 3, 6, 9 and 12 o'clock directions and the central ROI. Image noise was expressed by the standard deviation of CT value of large circular ROI. The smaller the values of image uniformity and noise, the better the image quality. Statistical description was applied to obtain data of the maximum, minimum, mean and standard deviation for the above mentioned two parameters. Y was defined as the difference between the average CT value of ROI in each direction and the average CT value of central ROI, which was used to represent the monthly changes of image quality.Results:The image uniformity and noise of CBCT images of the OBI system were generally stable during 2 years. For the 6 protocols of HQH, LDH, PSL, SDH, LDT and pevlis, the image uniformity was (21.5±1.0), (21.4±2.2), (21.3±0.9), (18.3±1.3), (3.4±1.9) and (7.2±1.9) HU, respectively. The image noise was (19.2±0.2), (41.0±0.3), (14.2±0.3), (38.2±0.2), (16.0±0.9) and (13.5±0.9) HU, respectively. The average image uniformity of LDT was the smallest, and the average image noise of pelvis was the smallest. Under the 6 scanning protocols, the average CT values of central ROI involved in image uniformity were (32.3±2.7), (24.0±3.3), (19.3±2.4), (11.1±2.5), (67.2±2.1), (-24.6±1.7) HU, respectively. The average CT values were stable. The standard deviation of Y was < 3 HU, suggesting that the stability of image quality was favorable every month.Conclusions:The image uniformity and noise of CBCT images for the OBI system are generally stable in 2 years. Among the 6 scanning protocols, LDT yields the best image uniformity, and pelvis has the lowest image noise.
