Objective To quantitatively study the influence of changes in probe position on the quality control test results of dental panoramic radiography and to provide a reference for analyzing the sources of deviations in quality control test results. Methods Eight different models of dental panoramic X-ray machines were selected for this study. The film analysis method was used to determine the position of the central axis of the main beam on the image detector. The position of the probe was accurately controlled through an auxiliary moving device. The tube voltage, radiation output, and half-value layer of the useful beam were measured for positions at the center of the beam; 1 cm upward, downward, left, and right from the center of the beam; and 2 cm upward, downward, left, and right from the center of the beam. Results The tube voltage, radiation output, and half-value layer had a maximum value at the center of the beam, with a decrease in the value as the position deviated from the center. There were significant differences in the probe position sensitivity between different models of dental panoramic radiography equipment. A 2 cm deviation in the probe position resulted in an impact on the measured tube voltage of less than 5.3 kV (5.8%) for less sensitive equipment. A 2 mm deviation in the probe position resulted in an impact on the measured tube voltage of less than 5.4 kV (6.0%) for sensitive equipment. Conclusion The probe position can lead to deviation in the quality control test results of dental panoramic photography. Therefore, determining the position of the central axis of the main beam on the image detector for accurate positioning of the probe is crucial for quality control testing.

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.

Objective:The Chinese pediatric mesh-type reference phantoms were developed and applied in the dose assessment of X-ray radiography.Methods:The 5- and 10-year-old Chinese pediatric mesh-type reference phantoms were developed based on the CT data. Based on the phantoms, the Monte Carlo method was applied to simulate the X-ray radiography to calculate the organ dose conversion coefficient and the effective dose conversion coefficient in different radiography conditions.Results:The 5- and 10-year-old Chinese pediatric mesh-type reference phantoms were developed, and the physical parameters were consistent with the national standard. The differences of the organ mass between the established phantoms and reference data were within 2%. The database of the pediatric chest posteroanterior projection and abdominal anteroposterior projection, tube voltage 60-90 kVp, total filtration 2.5~4 mmAl were simulated, and the difference between the effective dose conversion factor and the literature result was within 3%.Conclusions:The established Chinese pediatric mesh-type reference phantoms can be applied in the studies of radiation protection and clinical medicine and their result can provide an important reference for the dose assessment of the pediatric X-ray radiography.

Objective To study the methods to estimate absorbed dose to eye lens of infants from CT scanning using different protocols and try to find a practical quick way for estimating absorbed dose to eye lens.Methods By scanning one-year old anthropomorphic phantom using 7 kinds of different protocols,all TLDs were measured for final estimation of absorbed dose to eye lens using two different dose conversion methods.Meanwhile,linear regression equation was established between absorbed dose to eye lens and CTDI.Results Absorbed doses to eye lens of infants from children CT scanning using 7 kinds of different protocols were (9.96±0.69) mGy in head axis,(7.01±0.42) mGy in head helical,(12.60± 0.97) mGy in sinus,(12.97±0.42) mGy in inner ear,(0.63±0.03) mGy in neck soft tissue,(8.89± 0.44) mGy in cervical vertebra,and (0.34± 0.01) mGy in chest,respectively.There were statistically significant difference in doses among different groups (F =846.826,P ＜ 0.05).For different scanning locations,there was linear relation between absorbed dose to eye lens and CTDI(r=0.986-0.999,P＜ 0.05).Conclusions Absorbed dose to eye lens of infants from children CT scaning with single dose may not be above threshold dose.In addition,absorbed dose to eye lens can be estimated quickly by linear regression equation between absorbed dose to eye lens and CTDI.

Objective To analyze the radiation dose to contra-lateral breasts and estimate the incidence risk of contra-lateral breast cancer for women undergone unilateral breast cancer radiotherapy.Methods The radiation doses of contra-lateral breasts for 49 patients were counted and analyzed in a hospital,and the risk of contra-lateral breast cancer in different age groups that induced by radiotherapy was estimated based on BEIR Ⅶ model combined with the Chinese lifetime table.Results The prescribed doses for the patients were all 50 Gy.The mean dose to contra-lateral breasts ranged from 0.14 Gy to 3.59 Gy,with an average of (1.21 ±0.89) Gy,and the maximum point dose varied from 0.98 Gy to 45.27 Gy,with the average of (17.42 ±13.20) Gy.Both the maximum point dose and the mean dose obviously varied among the patients,and their correlation was significant (R =0.527,P =0.000).Furthermore,no significant differences of the mean dose was found among the ages (P ＞ 0.05).The lifetime attribute risks of contra-lateral breast cancer were estimated to be 2 449,1 857,994,446,173 and 55 for per 100 thousand women corresponding to the ages of 35,40,50,60,70 and 80,respectively.Conclusions In the radiotherapy for unilateral breast cancer,the dose delivered to the contra-lateral breast is about 1 Gy order of magnitude,the risk of contra-lateral breast cancer cannot be ignored for young women.Therefore,the irradiation dose of contra-lateral breasts should be controlled as less as possible in planning the treatment.

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.

Objective To study the shielding effect of equivalent thickness and size of lead glasses on eye lens of interventional radiologists.Methods Based on the human voxel phantom and MCNPX software,doses to eye lens of radiologists were simulated under different conditions of wearing lead glasses and beam projections,and measurements were performed with anthropomorphic phantom placed with eye lens dosimeters to verify simulation results.Results The results showed that the dose to eye lens reduced by a factor from 3 to 9 when the equivalent thickness of glasses ranged from 0.1 to 1.0 mm Pb with a len size of 20 cm2.The dose reduction factors (DRF) not only depended on the lead equivalent,but also on the beam projection of X-rays.However,the increase in DRF was not significant whenever the lead equivalent of glasses was larger than 0.35 mm.Furthermore,the DRF was proportional to the size of glass lens from 6 to 30 cm2 with the same lead equivalent.The simulation results were in well agreement with the measured ones.Conclusions For more reasonable and effective protection of the eye lens of interventional radiologists,a pair of glasses with a lead equivalent of 0.5 mm and large-sized lens is recommended.

Objective To study the relationship between the dose indicator of computed radiography (CR) and the entrance surface dose (ESD),and to build a model for estimating ESD based on this relationship.Methods Taking Kodak CR system as the research object,a theoretical model for estimating the ESD was established according to theoretical derivations,and the key parameters in the model were determined through experiments in a CR system.Further experiments in another CR system were also conducted to verify the model.Results The ESDs were not only dependent on the dose indicator provided by the CR system,but also influenced by other factors,such as tube potential,patient's body thickness and energy response of the imaging plate.The estimation results of the model agreed well with the experiment results,and the relative deviation was confirmed within 20％.Conclusions The dose indicator based model can provide a relatively fast and easy way for evaluating the doses of patients undergoing X-ray diagnoses with the CR system.

Objective To study the dose distribution characteristics formobile intra-operative radiotherapy accelerator (Mobetron) in an operating room,and to provide basic data for developing appropriate radiation protection measures and protection standard.Methods For most commonly used electron energy 9 MeV,TLD dosimeters were placed at 50,100,150 and 200 cm high plane,respectively.For each plane,the measurement points were selected at every 50 cm from the central axis at every 45° at eight different directions.Also different electron energies,such as 4,6,9 and 12 MeV,were taken into consideration at the plane at 100 cm height.After 10 Gy with a dose rate of 10 Gy/min were delivered,the TLD dosimeters were used to read out the data.Results For 9 MeV,at the phantom plane(100 cm high plane),the average doses were 169,756,395 and 241 μSv at 50,100,150 and 200 cm from the central axis,respectively.Themaximum deviation between the doses at 50 cm from the central axis in different angles and their average values were 9.1％.In the identical angle,the average doses of 50,100,150 and 200 cm high planes at the distance of 100 cm from central axis were 527,756,570 and 141 μSv,respecitvely.For the energies of 4,6,9 and 12 MeV,the average doses were 573,486,689 and 781 μSv at 100 cm from the central axis at 90° of 100 cm high plane.Conclusions For the same energy,the dose values at different directions were decreased by the minus exponential function law with the distance.The doses were uniformly distributed at different directions at the same distance from the central axis.The doses on the plane of 100 cm height were much higher than those at other heights,and the dose values were increased with the election energy.

Objective To study the calculation of the room shielding thickness of tomotherapy accelerator,a new type of radiotherapy facility,especially the impact of the beam block on the shielding design.Methods According to the relevant standards,combined with the room geometry,the shielding thickness was calculated without the presence of the beam block,considering the primary beam,the scattered beam and leakage.Meanwhile,the shielding thickness was also calculated as comparison with the presence of the beam block,based on the characteristics of tomotherapy facility and its radiation field.Results There was statistical difference between the shielding thicknesses calculated with the presence of the beam block and those without the beam block,to the primary beam direction including the south wall,north wall,the roof and the floor,the shielding thickness were decreased by 95.59%,63.63% ,80.73%and 51.30% ,respectively.Conclusions For the tomotherapy accelerator,the beam block could be of great help to minify the shielding thickness of the room.The radiation field of the tomotherapy facility could be used for the calculation to improve accuracy,and the shielding thickness can also be estimated by subtracting the initial shielding thickness without beam block of the beam block equivalent thickness in the primary beam direction alternatively.