OBJECTIVE: To investigate the influence of different scanning conditions on the image quality of medical electron accelerator cone-beam computed tomography (CBCT) and provide a reference for the selection of scanning conditions for different body parts. Methods Set different scanning conditions, the Catphan 503 phantom was scanned using CBCT parameters to analyze the influence of spatial resolution, noise, uniformity, spatial geometric accuracy, and low-contrast resolution on the image quality of CBCT. RESULTS: For the head, chest, and abdomen, with the increase in scanning parameter values, the noise value decreased by 47.4%, 26.1%, and 51.3% respectively, and the uniformity values decreased by 30.2%, 26.6%, and 47.9% respectively. The low-contrast resolution values decreased by 50.6%, 34.2%, and 12.0%. The influence of different scanning conditions on spatial geometric accuracy and spatial resolution is not significant. CONCLUSION Different scanning parameters have a certain influence on the image quality of medical electron accelerator CBCT. Lower scanning parameters can be selected based on individual patients to reduce the additional radiation dose, providing a reference for the safe application of CBCT image guidance in radiotherapy.
Cone-Beam Computed Tomography/instrumentation* ; Phantoms, Imaging ; Particle Accelerators

Objective:To assess the effects of the scanning parameters of cone beam computed tomography(CBCT)on image quality,positioning error and additional radiation dose for patients with cervical cancer after tube voltage was reduced,so as to explore scanning conditions that was suitable to patients with cervical cancer.Methods:Seventy-two patients with cervical cancer who received radiotherapy in Deyang People's Hospital from January 2020 to August 2022 were selected.According to different scanning parameters,they were divided into low-dose group A(120 kV,154.4 mAs),low-dose group B(120 kV,228.8 mAs)and conventional group[adopted business-supplied scan sequences(120 kV,675.8 mAs)].The CBCT scan image was obtained by decreasing the tube voltage and tube current,and reducing scanning angle.The registration results of positioning error of low-dose group A,B and conventional group on three directions included left and right(x-axis),head and foot(y-axis)and abdominal and back(z-axis)were respectively obtained,and the results were analyzed by variance analysis.The Catphan503 phantom of X-ray volumetric imaging(XVI)was used to measure the image quality of the corresponding 3 groups,and the further comparison was conducted.Results:There were no significant differences between the three groups in the scanning parameters on x,y and z axis directions for positioning error of patients with cervical cancer(P＞0.05).The scanning times of low-dose group A and B were approximately 1 minute,and the scanning time of conventional group was approximately 2 minutes.The noises of low-dose group A and B,and conventional group were respectively 36.51％,26.09％and 18.37％,and the radiation dose that was generated by CBCT image scanning in group A was correspondingly reduced.Conclusion:The reductions of scanning speed and collimator size of CBCT scanning parameters do not affect the positioning error and image quality,and it can decrease the scanning time and additional radiation dose of patients in undergoing radiotherapy.