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Objective To provide a theoretical basis for radiation health supervision through an analysis of the situation of computed tomography (CT) equipment quality control and CT room radiological protection in Guangdong Province, China in recent years. Methods We collected the data of 392 times of CT quality control and radiological protection testing by a third-party radiological health technical service institution in Guangdong Province from 2019 to 2021. We analyzed the levels of CT-owning hospitals, CT manufacturers, CT quality control test results, and the pass rate of radiation protection tests. Results The examined CT scanners were from different levels of hospitals in Guangdong Province, and were manufactured by nine major CT equipment manufacturers at home and abroad. The pass rate of CT room radiological protection was 99.88%, and the ambient dose equivalent rates of five monitoring points exceeded the limit, with four at the control room door and one at the shield wall of the room. The overall pass rate of CT equipment quality control was 99.49%, and the non-conforming parameters were the accuracy of positioning light and the deviation of reconstructed slice thickness. Conclusion In recent years, CT equipment quality control and room radiation protection in Guangdong Province have been at a high level.
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Objective To compare the differences in radiation doses from CT scanning between children of different age groups and adult patients by using both traditional radiation dose assessment parameters and size-specific dose estimates (SSDE).Methods A total of 406 patients undergoing lung CT examination were studied.They were sampled retrospectively and continuously from the Union Hospital and divided into six groups by age distritution (0-2,3-6,7-10,11-14,15-18,＞18 years old).The CTDIvol and DLP values were randomly sampled using MATLAB platform-based dicom data software.The SSDE and water equivalent diameter were also calculated according to the AAPM 220 Report.The differences in radiation doses from lung CT scaning between children and adult patients were analysed.Results The CTDIvol values for all age groups were significantly lower than the SSDE values.The differences were statistically significant (t =-36.36,-32.83,-30.36,-28.74,-23.89,P＜0.05).The SSDE values were 137％,94％,79％,57％ and 42％ higher than the CTDIvol values,respectively.The CTDIvol values for the adult group were also lower than the SSDE values,and the difference was statistically significant (t=-21.92,P＜0.05),and the SSDE value was about 41％ higher than the CTDIvol value.With the increased age,CTDIvol value,DLP value,Dw value and SSDE value for children of all age groups gradually increased and were significantly smaller than those for the adult group.The difference was statistically significant (F=63.39,203.28,89.27,103.44,P＜0.05).The conversion coefficient f for all age groups decreased significantly with age,which was significantly higher than that for the adult group,and the difference was statistically significant (F =109.83,P ＜ 0.05).Conclusions In lung CT scanning,the CTDIvol value significantly underestimated the radiation doses to children as compared to adults.CTDIvol values are more easily underestimated for younger patients.The SSDE method allows for more accurate reflection of the radiation doses to different patients,taking into account differences in the examined patient size.
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Objective To investigate the CT scanning parameters in hospitals at different levels in 15 provinces and cities in China and the doses to patients undergoing CT examination,in order to provide the basis for establishing CT diagnostic reference level suitable for our country.Methods As required in the implementation program for Technical Study on Medical Radiation Hazard Assessment and Control,the information on the patients examined and the CT scanning parameters in clinical practices were investigated.The CT dose index (CTDI100,CTDIW,CTDIVOL) of CT scanner was measured by using the CT ionization chamber.The dose length product (DLP) was calculated on the basis of the scan length of the patients examined.Results A total of 6 524 CT scanning procedures and 483 different types of CT scanning equipment were surveyed in 166 hospitals in 15 provinces in China.For head,chest,abdomen,and lumbar vertebrae,the average weighted CTDIW were 43,15,19 and 25 mGy,respectively,and the third quartile of CTDIw were 50,19,23 and 32 mGy,respectively.The average DLP were 540,397,503 and 376 mGy· cm,respectively.The third quartile of DLP were 659,525,632 and 479 mGy· cm respectively.Conclusions Through this survey,the doses to CT-examined patients in some provinces were basicly ascertained.The third quartile of doses to four body parts of the examined patients are different from the diagnostic reference level given in publications in other countries and regions.It is important to establish the CT diagnostic reference level suitable for our CT-examined patients according to Chinese national physical characteristics and therefor to promote the optimization of medical radiation protection in CT examination.
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Objective: To establish the relationship between the measured dose and the displayed dose in CT scans for children, and assess whether the displayed dose could be used as the basis to monitor the actual dose so as to provide data support for establishing a fast estimation method of actual dose in CT examination for children. Methods: The CT equipments with 16 slices detectors and 64 slices detectors of two manufacturers that often were used in clinical practice were selected in the research. CT dosage phantom that suited to children was used and pencil-ionization chamber was adopted to measure CT dose indexes of head scan and breast scan for children under various scan parameters. At the same time, displayed dose of the equipment was recorded and the ratio of measured dose and displayed dose was calculated . Results: The measured doses of the two manufacturers for head of children were 1.30-1.39 times and 1.17-1.26 times of displayed dose, respectively. And on thorax sequence, the measured doses were 1.95-2.27 times and 1.75-1.97 times of displayed dose, respectively. Based on above results, the measured dose of head was more close to the displayed dose than that of thorax sequence. Conclusion: In the CT examination of children, the ratio of measured dose to displayed dose shows good consistency under the different exposure conditions of same CT device model, and thus provides possibility to rapidly estimate the real dose on children according to the displayed dose in CT examinations.
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Objective: The purpose of the current study was to investigate the correction coefficient of the characterizations of multi-detector CT (MDCT). Methods: The dose profile of Siemens SOMATOM Definition Flash CT scanner was measured with CT-SD 16 detector under the conditions of different collimations, pitches and tube voltages in phantoms of different diameters, and the ratio between weighted CTDI∞and weighted CTDI100 was calculated. Results:The ratio between weighted CTDI∞and weighted CTDI100, which is growing for increasing beam collimation, was found to range from 1.123 to 1.162 in head phantom and range from 1.118 to 1.173 in body phantom. Conclusion: For MDCT, the use of CTDI100, which is one of the most commonly used characterizations of CT, has always underestimated the levels of radiation dose. Therefore, CTDI100 should be corrected.
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Objective To evaluate the patient dose from Hi-ART MV helical CT imaging in image-guided radiotherapy.Methods Weighted CT dose index (CTDI_W) was measured with PTW TM30009 CT ion chamber in head and body phantoms,respectively,for slice thicknesses of 2,4,6 mm with scanned range of 5 cm and 15 cm.Dose length products (DLP) were subsequently calculated.The CTDI_W and DLP were compared with XVI kV CBCT and ACQSim simulator CT for routine clinical protocols.Results An inverse relationship between CTDI and the slice thickness was found.The dose distribution was inhomogeneous owing to the attenuation of the couch.CTDI and DLP had close relationship with the slice thickness and the scanned range.Patient dose from MVCT was lower than XVI CBCT for head,but larger for body scan.Results CTDI_W can be used to assess the patient dose in MV helical CT due to its simplicity for measurement and reproducibility.Regular measurement should be performed in QA & QC program.Appropriate slice thickness and scan range should be chosen to reduce the patient dose.
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Objective To evaluate the variations of effective doges with the preset scanning parameters from linac-integrated kV cone beam CT( CBCT). Methods Weighted CT dose index(CTDIW) were measured with PTW TM30009 CT ion chamber in head phantom and body phantom, respectively, for different combinations of tube voltage, mAs, collimator and gantry rotation range. Dose length products(DLP) were derived from CTDIW and effective doses(E) were calculated by the DLP and EDLP. Results CTDIW and effective dose had the quadratical relationship with tube voltage, depending linearly on product of tube current and exposure time. Effective dose had close relationship with the collimator and the gantry rotation range. Both the DLP and ED for CBCT were lower than the reference dose level recommended for conventional CT. Conclusions Effective dose from CBCT has a close relationship with the scanning parameters. Optimal imaging parameters should be chosen according to the patient's anatomy to reduce patient dose.