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Objective To calculate the doses and their dose conversion coefficients for the personnel whose organs were under accidental exposure to three types of X-ray machines and two γ radiation sources, and to provide a simple method for rapid estimation of accidental doses. Methods The radiation source models of X-ray machines and two γ sources were established with the FLUKA simulation software and a Chinese reference voxel phantom was imported. The organ absorbed dose, dose conversion coefficient between organ absorbed dose and air Kerma, and conversion coefficient between organ absorbed dose and radiation source were calculated for a simulated scenario where the personnel were under antero-posterior exposure to radiation sources 1 meter away. Results For the lungs, heart, muscles, soft tissue, liver, skin, and brain, the conversion coefficient between organ absorbed dose and air Kerma was 0.30-1.19 (Gy/Gy). For X-ray machines, the conversion coefficient between organ absorbed dose and output for the six organs ranged from 6.12 × 10−3 to 2.90 × 10−2 Gy·m2/(mA·min). For γ radiation sources, the conversion coefficient between organ absorbed dose and activity for the six organs ranged from 1.12 × 10−8 to 7.01 × 10−8 Gy·m2/(GBq·s). Conclusion The conversion coefficient between organ absorbed dose and air Kerma and the conversion coefficient between organ absorbed dose and output or activity of a flaw detector can provide important dosimetric parameters for rapid assessment of similar radiation accidents.
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Objective To study the method of dose reconstruction in human body under the photon external radiation accident condition,and to verify the accuracy of the method for the local dose distribution.Methods Based on the open source Monte Carlo tool kit Geant 4 and using the human voxel phantom recommended by ICRP Publication 103,the dose reconstruction method under the condition of external radiation accident was studied to evaluate the average absorbed dose,organ absorbed dose and local dose distribution.To validate the code,several irradiation experiments were implemented in some standard radiation fields by putting TLDs in the tissue equivalent physical phantom ART.A voxel phantom was used to reconstruct the radiation doses,which was created based on the CT scan image of the ART phantom with resolution of 1.57 mm× 1.57 mm× 10.00 mm.The result of experiment were compared with those of dose reconstruction simulation.Results The relative uncertainty of the measured values was 10.9％.The relative uncertainty of the dose reconstruction simulation values was 7.10％ at the non-tissueinterface area and 16.6％ at the tissue-interface area.For 451 measuring points,the average of the simulated value divided by the measured value was 0.972,with the standard deviation of 0.083 8.In the range of 0.95-1.05,0.90-1.10 and 0.80-1.20,and the proportions were 49.2％,79.4％ and 96.4％,respectively.Conclusions The method of Monte Carlo dose reconstruction based on human voxel phantom meets the accuracy requirement of actual uses both at the whole body or organ level and at the local dose distribution level.It can be used as a powerful tool for dose assessment of the exposed people in an external radiation accidents and provide support for diagnosis and treatment.
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Objective@#To study the lumber spine imaging process of dual-energy X-ray absorptiometry (DXA) and parameters used to optimize the image quality.@*Methods@#A computational voxel phantom was constructed from patient computed tomography (CT) data. Using the Monte Carlo radiation transport method, a dual energy x-ray beam was simulated to scan the phantom of lumbar spine to generate a bone density image. The Figure of Merit (FOM) of each image was claculated. Parameters including the combination of the high and low energy tube voltage, the thickness of Cu filter, and the ratio of two beam energy incident photon number were optimized, which based on FOM.@*Results@#FOM reaches a minimum of 1.59 × 10-2 with the tube voltage combination of 75 and 200 kVp. With the thickness of the Cu filter from 0 mm to 3 mm, FOM decreases from 6.30×10-2 to 1.87×10-2, showing a gradually slow-down trend. With the incident photon number ratio (low energy/high energy) increasing from 1∶3 to 19∶1, FOM decreases firstly and then increases, reaching a minimum of 1.40×10-2 at 3∶1.@*Conclusions@#According to the simulation results, the combinations of low tube voltage from 70 kVp to 85 kVp and high tube voltage from 160 kVp to 200 kVp, 0.3 mm Cu filter and beam incident photon number ratio from 1 to 5 can yield the best lumbar spine image quality with the lowest patient dose.
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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.