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@#<b>Objective</b> To apply a phantom for dose measurement in interventional therapy for pediatric vascular diseases, and calculate the effective dose (<i>E</i>) and conversion coefficient of dose area product (DAP) to <i>E</i>, and to provide a dose reference for studying radiation dose and radiation protection in children. <b>Methods</b> Thermoluminescent dosimeters were placed in the organs of the phantom. Low-, medium-, and high-dose groups were set for three types of vascular anomalies based on the duration of fluoroscopy. Digital subtraction angiography was used to simulate exposure conditions at different dose levels. The organ dose was measured, and the effective dose was calculated. <b>Results</b> For the three groups of vascular anomalies in the head and face, the red bone marrow doses were 8.15, 30.34, and 43.53 mGy, respectively, the effective doses were 12.88, 47.84, and 73.12 mSv, respectively; and the average conversion coefficient of DAP to <i>E</i> was 2.16. For the three groups of vascular anomalies in the trunk, the red bone marrow doses were 2.11, 15.62, and 31.21 mGy, respectively; the effective doses were 12.39, 70.56, and 134.60 mSv, respectively, and the average conversion coefficient of DAP to <i>E</i> was 3.03. For the three groups of vascular anomalies in the lower extremities, the red bone marrow doses were 3.58, 6.50, and 12.28 mGy, respectively, the effective doses were 3.64, 7.04, and 14.85 mSv, respectively, and the average conversion coefficient of DAP to <i>E</i> was 0.73. <b>Conclusion</b> Patient dose and DAP-to-<i>E</i> conversion coefficient are in the following order: vascular anomalies in the trunk > vascular anomalies in the head and face > vascular anomalies in the lower extremities. The dose data obtained can be used to estimate children’s radiation exposure.
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Background The thyroid gland is one of the organs sensitive to ionizing radiation, and there are few studies on the effects of long-term exposure to low doses of ionizing radiation on the thyroid gland of radiation workers. Objective To investigate thyroid abnormalities in workers in medical radiology departments in Guangdong Province and to identify potential influencing factors of thyroid abnormalities. Methods A total of 1657 radiation workers from 48 hospitals in Guangdong Province were selected as survey subjects using convenience sampling, and their personal dose monitoring results and health examination information were retrospectively analyzed to determine the factors affecting thyroid abnormalities. Results The M (P25, P75) of thyroid absorbed dose (DT) was 1.55 (0.65, 3.96) mGy in the 1657 investigated workers. The attribute-specific medians of DT were 1.29, 1.38, 1.99, and 3.51 mGy for departments of diagnostic radiology, interventional radiology, radiotherapy, and nuclear medicine, respectively; and 1.10, 1.55, and 1.80 mGy for job titles of nurse, technician, and physician, respectively. Differences in DT by gender, age, years of radiological work, age of radiation exposure onset, occupational category, and job title were statistically significant (Z=−6.35, H=708.52, 918.20, 31.19, 95.64, 39.28, P<0.05). The positive rate of thyroid abnormalities in investigated workers was 46.53% (771/1657). Among them, the positive rate of abnormal thyroid function was 22.87% (379/1657), that of abnormal thyroid morphology was 33.98% (563/1657), and that of thyroid nodule was 26.55% (440/1657). The differences in thyroid abnormality rates by gender, age, years of radiation work, age of radiation exposure onset, DT, and job title of radiation workers were statistically significant (χ2=51.89, 49.64, 20.54, 18.29, 12.07, 16.16, P<0.05). The differences in abnormal thyroid function positive rate by gender, age of radiation exposure onset, and job title were statistically significant (χ2=26.21, 6.21, 8.32, P<0.05). The differences in the positive rates of abnormal thyroid morphology and nodules were statistically significant by gender, age, years of radiological work, age of radiation exposure onset, DT, and job title (abnormal thyroid morphology, χ2=40.24, 64.17, 37.63, 15.17, 19.28, 15.05; nodules, χ2=31.41, 77.98, 42.11, 19.16, 21.70, 13.52, P<0.05). The positive rates of thyroid abnormality, thyroid morphology abnormality, and nodules all showed a linear increasing trend with increasing age, years of radiation work, and age of radiation exposure onset (P<0.05). The results of logistic regression analysis indicated that the factors influencing thyroid abnormalities were female (OR=2.17, 95%CI: 1.72-2.74), increased years of radiological work (OR=1.04, 95%CI: 1.03-1.06), onset of radiation exposure in age groups of 30-34 and ≥35 years (OR=1.63, 95%CI: 1.12-2.37; OR=2.58, 95%CI: 1.74-3.29), and working in department of diagnostic radiology (OR=1.40, 95%CI: 1.07-1.84). Conclusion Long-term exposure to low doses of ionizing radiation has an effect on thyroid abnormalities in medical radiation workers. Among them, being female, physicians, and working in department of diagnostic radiology are at a higher risk of abnormal thyroid function; being female, increased years of radiation work, and radiation exposure onset at age ≥30 years are associated with a higher risk of reporting abnormal thyroid morphology.
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Objective:To investigate the effects of organ dose modulation (ODM) on image quality and radiation dose to lens during sinus CT scanning.Methods:The GE Revolution EVO CT was used to scan the anthropomorphic head with ODM turned off as the control group and ODM turned on as the observation group. With different parameter combinations of tube voltage (140, 120, 100 kV), noise index (N17, N18), pitch (0.531, 0.969 at 20 cm collimation width, 0.516, 0.984 at 40 mm collination width), 24 series of images were acquired respectively. The tube current (mA) valuesat the anterior (A), left (L), posterior (P) and right (R) positions, volume CT dose index (CTDI vol) and dose length product (DLP) were recorded. Average CT values (AV), standard deviation (SD), signal-to-noise ratio (SNR), contrast to noise ratio (CNR) and image quality factor (FOM) of ROI were calculated. Double blind method was used to evaluate the edge sharpness, soft tissue level, noise and artifact on a subjective scale of 3 points. Results:For the combinations of different scanning parameters, the radiation dose of the observation group was lower than that of the control group. The tube current attheposition A for the observation group was lower than that of the control group, and the difference was statistically significant ( t=2.28, P<0.05). The differences oftube currentsatposotions of L, P and R, CTDI vol and DLP values in twogroupswere not statistically significant ( P>0.05). There were no significant differences in SD, SNR, CNR and FOM between the two groups of images ( P>0.05). There were no significant differences in the subjective scores of edge sharpness, soft tissue gradation, noise and artifacts between the two groups ( P>0.05). Conclusions:ODM technique can effectively reduce the radiation dose of eye lens without decompromising the image quality, which could meet the requirements of diagnosis, and accord with the principle of radiological protection optimization.
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Objective:To calculate the conversion coefficient from dose area product (DAP) to organ absorbed dose by Monte Carlo method in order to conveniently estimate doses to patient organ during coronary intervention procedure.Methods:The Geant4 Monte Carlo simulation kit was used to calculate the organ absorbed dose conversion coefficients by simulating exposure scene.Results:The conversion coefficients used in coronary angiography (CAG) for lung, bone marrow, liver and heart were (0.283±0.068), (0.169±0.049), (0.110±0.077) and (0.080±0.032) mGy/(Gy·cm 2) for male, and (0.376±0.121), (0.192±0.056), (0.153±0.105), and (0.102±0.033) mGy/(Gy·cm 2) for female, respectively. These were similar to those in the case of percutaneous coronary intervention (PCI). The DAPs for different interventional procedures were statistically significant ( t=-6.012, P<0.05). The DAPs for difference gender groups had no statistically significant ( P>0.05). Conclusions:Conversion coefficient for organ absorbed dose has little correlation with CAG and PCI in the same sex group. Dose conversion coefficients for female group are greater than those for male group in the same procedure. Conversion coefficients from DAP to organ absorbed dose calculated with Monte Carlo method can provide convenience for rapidly estimating the organ absorbed dose to clinical patients.
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@#The radiation risk caused by CT examination is of great concern. Organ dose is considered to be the most significant technical parameter for quantifying the patient radiation dose and assessing the corresponding risk. At present, the methods to obtain patient organ dose caused by CT examination mainly include physical phantom measurement, direct human body measurement, dose conversion coefficient, Monte Carlo simulation, and dose calculation software. Although different methods have their own characteristics and application, the individualization of organ dose is always the goal of radiation protection and dosimetry research. Patient-specific phantom developed with artificial intelligence and GPU-accelerated Monte Carlo simulation make it possible to calculate the patient-specific organ dose, and the patient-specific organ dose extrapolated by the CT detector signal provides a new solution.
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Objective:To investigate the uncertainty of the dose measurements of superficial organs and the image noise in CT scanning.Methods:GE Revolution CT was used to perform 20 repeated scans on the isolated skull specimen in sequential and helical mode. The chest phantom was scanned for 45 times with the pitch 1.0 and the collimation 80 mm for two scanners (GE Revolution CT, Philips Brilliance iCT) and 40 mm for the Siemens Somatom Definition Flash CT. The volume CT dose index (CTDI vol) was maintained during the above scannings. A dosimeter was used to measure the dose at the position of the right eye lens of the specimen and the center of right breast of the chest phantom. The position of dosimeter sensor remained unchanged. The standard deviation of CT values (image noise) in the air region of cross-sectional images at the center of the sensor reconstructed with lung/soft tissue algorithms were measured. The mean values ( Av), standard deviations ( SD), coefficients of variation ( CV) and relative ranges ( RR) of the dosimetric values and the standard deviations of CT values of 3, 5, 10, 20, 30 and 45 scans were calculated. Pearson and Spearman correlation analysis were used to evaluate the correlation between the dosimetric values and the standard deviations of CT values. Results:The measured dosimetric values of the skull specimen were almost unchanged in the sequential scannings. The relative range of dose in helical mode was 10.67%. The relative ranges of the measured values of the three CT scanners for 45 scans reached 43.83%, 25.31%, and 14.32%. The standard deviations of CT values of the lung/soft tissue images varied greatly and the differences were not completely related to the dosimetric values.Conclusions:The dosimetric values of superficial organs were stable in the sequential scanning mode. The dose measurements of superficial organs and the image noise changed greatly in helical scanning mode.
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Objective:To study the feasibility that using size-specific dose estimation (SSDE) to estimate organ dose and effective dose in coronary CT angiography (CTA).Methods:Totally 421 consecutive patients with coronary artery CTA were included and retrospectively analized. All patients were scanned using the 3rd generation dual-source Force CT with prospectively ECG gated axis scan mode. The size specific dose estimation(SSDE) for each patient was conducted by calculate water equivalent diameters with Radimetrics. The organ doses of heart, lung, liver and breast, were estimated with Monte Carlo method. Patient-specific effective dose was calculated as a weighted sum of simulated organ doses with the coefficients from ICRP 103. Linear correlation analysis was used to validate the relationship between SSDE and organ doses as well as effective dose, and to derive coefficients for patient specific dose estimation. The mean error rate was used to evaluate estimation accuracy.Results:The CTDI vol, SSDE and effective dose were (16.8±8.7)mGy, (20.8±8.8)mGy and (4.4±2.9)mSv, respectively. The linear fitting formula for estimating organ dose based on SSDE were: Y=1.2 X-6.4 ( R2=0.91, P<0.05, mean error 0.1%) for heart, Y=1.4 X-7.4 ( R2=0.91, P<0.05, mean error 7.9%) for breast, Y=0.89 X-4.6 ( R2=0.86, P<0.05, mean error 8.3%) for lung, and Y=0.36 X-1.8 ( R2=0.64, P<0.05, mean error -17.9%) for liver. The linear fitting formula for estimating the individual effective dose based on SSDE were: Y=0.21 X-1.2 ( R2=0.92, P<0.05, mean error 0.2%) for men, Y=0.39 X-2.2 ( R2=0.93, P<0.05, mean error 1.7%) for women. Conclusions:In coronary artery CTA, the absorbed dose of the organs and patient specific effective dose could be estimated with SSDE and the corresponding conversion coefficients, which will help to achieve personalized assessment and precise management of patient radiation dose and risk in clinical practice.
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Objective: To investigate the effectiveness of organ dose modulation (ODM) on dose reduction and image quality in CT plain scanning of head. Methods: A total of 100 patients who underwent head CT plain scanning were continuously collected. The patients were randomly divided into experimental group and control group with 50 cases in each group. ODM was applied in orbital region during CT plain scanning in experimental group, while CT plain scanning of head was performed in control group, and the parameters of scanning remained unchanged in both groups. Tube currents on different directions (anterior, posterior, left and right) of the orbital region were recorded, and volume CT dose index (CTDIvol) and dose length product (DLP) were recorded to calculate effective dosage (ED). ROI of the pons and bilateral cerebellar hemispheres were selected for measurement and calculation of objective noise and SNR. The imaging quality was subjectively graded as 1-5 points. Results: In experimental group, the tube current on anterior direction of head CT scanning area was significantly lower than that in control group (t=9.72, P=0.01). There was no statistical difference of CTDIvol, DLP, ED (all P>0.05), nor of objective noise in the pons and bilateral cerebellar hemispheres on posterior cranial fossa level and SNR between the two groups (all P>0.05). Subjective assessment showed all the image quality scores were ≥3 and could meet diagnostic needs in the two groups. No statistical difference of image quality score was found between the two groups (Z=0.25, P=0.31). Conclusion: During CT plain scanning of head, the application of ODM can reduce the tube current in the direct direction (anterior), thereby reduce the radiation dose in the orbital region and obtain image quality that can meet diagnostic requirements, meanwhile protect the sensitive organs.
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Objective To investigate the effects of different tube voltages on the dose of superficial radiation-sensitive organs and image quality when using organ dose modulation( ODM) in chest CT. Methods Based on clinical chest CT protocol with the sameother parameters, chest phantom was scanned using 140, 120, 100, and 80 kv ( 100 kV was the recommended by the CT system) without ODM ( ODM off ) or with ODM from the starting layer to the breast area ( ODM part ) . A long rod ionization chamber was placed iat a fixed position in front of the right breast area. The scans were repeated for 7 times with each group of scanning parameters and dose values were measured for each scanning, the CTDIvol and breast skin dose measurements( D) were recorded. Coronal images of 5 mm thickness for the lung and soft tissue algorithms were reformatted. The images were divided into 8 parts along the z axis direction, the contrast noise ratios( CNR) for every region were measured. For CTDIvol , D, CNR for different ODM and tube voltage scanning modes, two factor non-repeat test ANOVA was performed. LSD method was used for comparison among groups. Results The CTDIvol was lowest at 80 kV, and the breast skin dose measurement was lowest at 100 kV, CTDIvol decreased in turn from140 to 80 kV ( F=105. 5795, P<0. 05) . The breast skin dose measurement decreased in turn from140 to 100 kV, but increased instead at 80 kV. The difference was statistically significant(F=27. 736, P<0. 05). Compared with ODM off , the CTDIvol and D for ODM part both declined and the differences were statistically significant ( F=39. 732, 81. 961, P<0. 05). The CNRs of the lung and soft tissue images decreased at every tube voltage(F=12. 809, 11. 261, P<0. 05 ) . The CNRs decreased from140 to 100 kV, but there was no statistical difference( P>0. 05) , and the difference was significant at 80 kV( P<0. 05) . Compared with ODM off, the CNRs of lung and soft tissue algorithm images with ODM part decreased, withnot statistically significant differences ( P>0. 05 ) . Conclusions In clinical practice, with the tube voltage not less than the recommended(100 kV), the optimal reduction of breast radiation dose can be achieved by reducing kV and using ODM on the premise of resonable image quality.
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Objective To estimate effective and organ doses to prostate cancer patients result ing from the whole-body 18F-Choline,11C-Choline and 68Ga-PSMA PET-CT examinations.Methods A total of 150 prostate cancer patients who underwent PET-CT scanning from May 2017 to June 2018 were retrospectively analyzed.They were divided into three groups,each with 50 patients,according to the type of positron radiopharmaceuticals injected.All patients used the same PET-CT scan protocol.PET component dose was calculated by using OLINDA/EXM (version 1.1) software which was based on the MIRD method.The CTDI values were measured by the standard CT phantoms and computed by ImPACT (version 1.0.4) CT,and ImPACT was used for dose calculation from CT.The tissue weighting factors according to ICRP Report 103 were used for effective dose calculation.Results The effective dose and organ equivalent dose from 18F/11C-Choline and 68Ga-PSMA PET/CT examinations were estimated.The voltage and current of Topogram scan were 120 kV and 35 mA,respectively,as well as 120 kV and (135.6±9.4) mA for low-dose CT scan.The injected activity of 18 F-Choline,11 C-Choline and68Ga-PSMA was (279.2±13.2),(350.2±39.9) and (186.8±19.4) MBq,respectively.The effective dose was (5.0±0.2),(1.6±0.2) and (3.0±0.3) mSv,respectively (F=837.0,P＜0.001).The CT effective dose was (11.4±0.2) mSv.The total effective dose for three groups were (16.4±0.3),(13.0±0.3) and (14.4±0.4) mSv,respectively.The mean organ equivalent doses were statistically significantly different among groups (F=381.2-1 637.7,P＜0.001).The highest organ equivalent dose was to kidney for18F-Choline and68 Ga-PSMA PET/CT scans and thyroid for11 C-Choline PET/CT scan.Conclusions The effective dose to the prostate cancer patients who underwent PET-CT scanning was from 13.0 to 16.4 mSv,with vast majority of these doses coming from CT scans.The lowest radiation dose to the patients was caused by 11C-Choline PET-CT examination,suggesting that it would be a potential prostate cancer PET radiotracer.
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Objective To explore the effects of detector width and pitch on radiation dose and image quality when using organ dose modulation (ODM) technology in a wide?area detector CT scanning. Methods Based on the clinical chest scan protocol,3 sets of scans of the chest phantom were performed using any combination of two detector width (40 mm and 80 mm) and pitch (0.500,1.000 and 1.375) with the same parameters:1 Do not use ODM technology (ODM off),2 open ODM (ODM part) 240 mm from scan start layer to breast area,3 open ODM (ODM all) in full 320 mm scan range. A long rod ionization chamber was placed in the fixed position in front of the right breast area. The scanning parameters of each group were measured 7 times, and the volume computed tomography dose index (CTDIvol) and breast skin dose measurement values D were recorded and the mean was calculated and recorded as Dav. The coronal 5 mm thick images of lung and soft tissue algorithms were reformed. It was divided into three parts in the Z?axis direction, and the contrast?to?noise ratio (CNR) and figure of merit (FOM) were measured separately. Independent sample t test was used for CTDI and breast skin doses D and CNR at both detector widths. ANOVA was used for dose and CNR of three sets of pitch (0.500, 1.000, and 1.375) and the three ODM techniques. Result The FOM factor was the largest when using an 80 mm detector with a pitch of 0.992 and partially turning on the ODM. The radiation dose of the three ODM groups decreased in turn, and the effect of ODM on CTDIvol (P=0.019) and breast skin dose (P=0.002) was statistically significant. The width of the detector increased and the dose was increased. The width of the detector was statistically significant for CTDIvol (t=-2.723, P=0.015). There was no statistically significant effect on the breast skin dose (t=-0.908, P=0.377). The effects of the pitch were not statistically significant for CTDIvol (P=0.254) and breast dose (P=0.146). The CNR of the three ODM groups decreased in turn, and the effect of ODM on the soft tissue image CNR was not statistically significant (P=0.146). The CNR of lung algorithm image (P=0.030) had significant effects. The multiple comparisons:only ODM all was significantly different from ODM off (P=0.009). With the increase of detector width,the values of CNR increased,the values of CNR (t=-4.128,P=0.001) of lung images were significantly affected. The effects on the soft tissue images were not statistically significant (P=0.187). There was no statistically significant difference in the effect of pitch on the CNR (P=0.660) of the lung images. The effects of the pitch on the values of CNR of soft tissue images (F=11.756,P=0.001) were statistically significant. By multiple comparisons, the difference of CNR between 0.500 (P=0.000) and 1.375 (P=0.013) was statistically significant compared with that when the pitch was 1.000. There was no significant difference among the three ODM modes (P>0.05) on the values of CNR of upper and middle parts of lung and soft tissue arithmetic images. The differences of CNR between ODM all and the other two groups were statistically significant (P<0.05) on the bottom part of images. Conclusion The changes of detector width and pitch will affect the organs dose modulation technique, and then affect the radiation dose and image quality. When using 80 mm detector with the pitch of 0.992 and partially turning on ODM in chest CT scan,achieving the optimized benefits of quality and dose.
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Objective To estimate the lifetime attributable risk (LAR) of lung cancer,stomach cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan.Methods Chest CT images of children was retrieved from the picture archiving and communication system (PACS) and the average CT number and area of the region of interest (ROI) were read on the CT work station.Water equivalent diameter were calculated according to the method recommended by the American Association of Physicists in Medicine (AAPM).Furthermore,the size-specific dose estimation (SSDE) was made based on the water equivalent diameter and the volume computed tomography dose index(CTDIvol).Based on the method recommended by Caro Franck,the SSDE then was converted into average organ doses to lung,stomach,liver,thyroid,breast and blood for children at different ages and of different sex undergoing chest CT scan.On the basis of average organ dose,the cancer risk prediction model from the National Academy of Science's Biological Effects of Ionizing Radiation-Ⅶ (BEIR-Ⅶ) was used to predict the LAR for different cancers mentioned above.For lung cancer,gastric cancer,liver cancer and leukemia,the calculating sequence was from average organ dose to excess relative risk (ERR) to LAR,whereas for the thyroid cancer and breast cancer,the sequence was from ERR to average organ dose to LAR.Results The average organ dose to lung,stomach,liver,thyroid,breast and blood for children at different age and of different sex undergoing chest CT scan was obtained.The age had a statistically significant impact on the SSDE (t =24.28,P ＜ 0.05),but sex has not (P ＞ 0.05).LAR for lung cancer,gastric cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan was obtained,among whom the LAR for thyroid cancer and breast cancer was relatively high.The LAR for women breast cancer was 10.9 per 100 000 persons for 1 year old children,30.8 per 100 000 persons for 5 years old and 34.5 per 100 000 persons for 10 years old.Conclusions With introduction of new technologies,the radiation dose due to chest CT scan is on the decline.But the induced radiation dose is still significant compared with general diagnostic radiography.The risk of cancer still deserves more attention and should be taken into consideration in the justification of diagnostic radiology.
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Objective To study the effects of organ dose modulation (ODM) technique on dose reduction of the breasts and the related thoracic image quality in female chest CT.Methods One hundred and twelve female patients with chest CT were enrolled in this study and divided into two groups according to the order:control group (n =56,using conventional scan) and experimental group (n =56,using ODM technique).The tube currents in different directions (A/L/P/R) were analyzed in the two groups.The effects of ODM on the radiation dosage and image quality were assessed.Results The tubc currents in anterior and posterior direction were both (128 ± 43)mA in the control group.However,the tube current in the anterior was lower than that in the posterior in experimental group (t =-18.701,P ＜0.01).The tube currents in all direction in the experimental group were all lower than those in the control group (t =11.71-20.22,P ＜0.01).The CTDIvol and E in the experimental group were lower than those in the control group(t=3.58,3.55,P ＜0.05).There were no significant differences for the objective and the subjective scores between two groups (P ＞ 0.05).Conclusions ODM technique could protect the female breasts by reducing the radiation dose without image quality degrading during chest CT scan.
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Objective To compare patient organ doses and entrance surface dose conversion coefficients in conventional radiography using medical internal radiation dose (MIRD) phantom and voxel human phantom.Methods The voxel phantom was adapted to the Monte Carlo transport code to simulate the organ doses and entrance surface dose in five common projections, and thus the dose conversion coefficients between the entrance skin dose and organ dose were calculated.The results were compared with the reported mean values which were simulated using MIRD phantom.Results The dose conversion coefficients values of organs covered or partially covered by the X-ray field ranged from 0.149-0.650 in chest postero-anterior projection, 0.067-0.382 in chest left lateral projection, 0.023-0.374 in chest right lateral projection, 0.035-0.431 in abdominal antero-posterior projection, 0.083-0.432 in lumbar spine antero-posterior projection.In chest postero-anterior projection, significant differences were most obviously observed in lung, the dose conversion coefficients difference was 54.3％.In chest left lateral projection, the dose conversion coefficients difference of liver was greatest, which was 54.5％.In chest right lateral projection, the dose conversion coefficients differences of stomach wall was most obviously 63.8％.In abdominal antero-posterior projection, dose conversion coefficients discrepancy was most obviously observed in spleen, with the value of 65.0％;while in lumbar spine antero-posterior projection, the dose conversion coefficients differences of stomach wall was most obviously 43.7％.Conclusions Compared with the stylized MIRD phantoms, the anatomical realism in voxel phantom is evident.Therefore, the dose conversion coefficients calculated by voxel phantoms are more accurate and scientific in conventional radiology.
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Objective To explore the organ doses and their distributions in different projections of CT scans.Methods The CT values were measured and the linear absorption coefficients were derived for the main organs of the anthropomorphic phantom to compare with the normal values of human beings.The radiophotoluminescent glass dosimeters were set into various tissues or organs of the phantom for mimic measurements of the organ doses undergoing the head,chest,abdomen and pelvis CT scans,respectively.Results The tissue equivalence of the phantom used in this study was good.The brain had the largest organ dose undergoing the head CT scan.The organ doses in thyroid,breast,lung and oesophagus were relatively large in performing the chest CT scan,while the liver,stomach,colon and lung had relatively hrge organ doses in abdomen CT practice.The doses in bone surface and colon exceeded by 50 mGy in a single pelvis CT scan.Conclusions The organ doses and their distributions largely vary with different projections of CT scans.The organ doses of colon,bone marrow,gonads and bladder are fairly large in performing pelvis CT scan,which should be paid attention in the practice.
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OBJETIVO: Avaliar a freqüência das incidências radiográficas realizadas nos seios da face de pacientes pediátricos em hospitais de Belo Horizonte, MG, as condições de radioproteção, as técnicas radiográficas empregadas, o kerma no ar de entrada e as doses nos órgãos mais expostos. MATERIAIS E MÉTODOS: Foram coletados os dados dos pacientes e parâmetros de técnica radiográfica empregados em exames de crianças de 1 a 16 anos de idade, em cinco salas de quatro hospitais da cidade, observando, também, aspectos de proteção radiológica. O kerma no ar de entrada foi estimado a partir dos rendimentos dos tubos de raios-x e as doses nos órgãos utilizando o software PCXMC. RESULTADOS: Os valores médios do kerma no ar de entrada para as cinco salas foram, respectivamente, 1.398 µGy, 829 µGy, 877 µGy, 1.168 µGy e 3.886 µGy para pacientes entre 1 e 5 anos de idade. CONCLUSÃO: Foi constatado que as incidências mento-naso e fronto-naso são comumente solicitadas em conjunto, na maioria dos hospitais, o que confere dose significativa para os pacientes. Os riscos para os pacientes podem ser diminuídos mediante a utilização de cilindros de colimação, a não-utilização de grades antiespalhamento, o emprego de altos valores de tensão e baixos valores de tempo.
OBJECTIVE: The present study was aimed at evaluating the frequency of radiographic assessment of paranasal sinuses in pediatric patients in hospitals of Belo Horizonte, MG, Brazil. Additionally, aspects regarding radiation protection conditions and radiographic parameters were evaluated, and entrance air kerma and organ doses were estimated. MATERIALS AND METHODS: Patients' data and parameters of radiographic technique employed in the assessment of children in the age range between 1 and 16 years were collected in five examination rooms of four hospitals in Belo Horizonte, also taking into consideration the radiation protection aspects. Entrance air kerma calculation was based on the x-ray tubes output, and organ doses were estimated with the PCXMC software. RESULTS: Mean entrance air kerma values found in the five rooms were, respectively, 1398 µGy, 829 µGy, 877 µGy, 1168 µGy and 3886 µGy for patients with ages between 1 and 5 years. CONCLUSION: Most frequently, mento-naso and fronto-naso views are requested in conjunction in the majority of hospitals, which increases the radiation dose to the patients. It may be concluded that the risks for patients can be reduced by means of the utilization of an appropriate x-ray field, non-utilization of antiscattering grids, selection of high voltages and lower exposure times.