Long-term Constancy Analysis of CT Numbers for Cone-beam CT Images of a Varian OBI System
SHI Fei-yue1,TIAN Shu-chang2,JIN Xun3,QIN Hang2,QIN Wei1
1. Radiation Therapy Center, Nanjing First Hospital, Nanjing, Jiangsu 210006, China
2. Department of Medical Equipment, Nanjing First Hospital, Nanjing, Jiangsu 210006, China
3. The Second Clinical Medical College, Nangjing University of Chinese Medicine, Nanjing, Jiangsu 210023, China
Abstract：The long-term constancy of CT numbers for cone-beam CT images of Varian on-board imager (OBI) system were evaluated, by analyzing the data of CT numbers for seven materials obtained from long-term quality assurance (QA) tests. QA tests for an OBI system equipped by the Varian Clinac iX linear accelerator were carried out with the Catphan504 phantom monthly. CBCT images were obtained with three scan protocols: high-quality head (HQH), standard-dose head (SDH) and Pelvis for the phantom. The DoseLab software was utilized to analyze the 36 series of CBCT images acquired from Mar. 2017 to Feb. 2018, and the CT numbers (Y) and corresponding difference from standard CT numbers (ΔY) for the seves materials were obtained.The datas were analysised by statistical method , and the mean, standard deviation and range values of Y and the mean of ΔY were obtained after calculation for the seven materials with three scan protocols. The results showed that the constancy of CT numbers of the CBCT images from the Varian OBI system was in good condition in 12 months by and large, the scan protocols of SDH and Pelvis were suitable for QA and metering tests of CBCT image quality, the difference between CT numbers of CBCT images with HQH and the standard CT numbers varied greatly with the increasing of relative electron density of material.
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2020, Vol. 41 
