Objective:To estimate the organ doses and effective doses to different-age children during cardiovascular interventional radiological procedures under some specific exposure conditions, and explore the main influencing factors on the doses.Methods:Based on the paediatric reference computational phantoms recommended in the ICRP Publication 143, several specific exposure models of cardiovascular intervention were built, and the Monte Carlocook MCNPX 2.7.0, was used to calculate the organ doses and effective doses for 1-, 5-, 10- and 15-year-old children. To validate the simulation result , an experiment was implemented by putting the thermoluminescent dosimeters in a 5-y old phantom (ATOM 705-D) manufactured by the CIRS Inc. in the USA.Results:Both the height and weight of the reference children for 1-, 5- and 10-year-old provided for by Chinese national standards are nearly in consistency with those recommended by ICRP, and even for the 15-year-old, the maximum relative deviations of the height and weight are only -1.9% and -5.7%, respectively. Under the exposure condition where the focal spot to image receptor distance (SID) was 90 cm, the length of square field of view (FOV) was 30 cm with a dose area product (DAP) of 45 Gy·cm 2, the relative deviations between simulated and measured doses to main organs/tissues within the irradiation filed were within ±6.7%. Under the same exposure conditions, the younger the children, the larger the organ doses and effective doses, and the effective doses could vary by a factor of about 5 among the 4 age groups. The conversion coefficient between the organ dose and the value of DAP was not only closely related to the age of children, but also affected by the FOV. Conclusions:In combination with the paediatric reference computational phantoms and the exposure models of cardiovascular intervention, the Monte Carlo method can be used to calculate the doses to children undergoing cardiovascular interventional radiological procedures. The information on the values of DAP and FOV as well as the directions of projection are needed for more accurate estimation of the exposure doses.

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 survey the current dose level for adults undergoing posteroanterior (PA) chest X-ray photography in Shanghai,and to analyze the main factors affecting the dose level.Methods The thermoluminescence dosimeters (TLDs) were deployed to measure entrance surface dose (ESD) in the center of radiated fields.According to the numbers of three types of X-ray equipment and their distribution among different grade hospitals in Shanghai,the ESDs were surveyed for 1032 adults undergoing examination of PA chest X-ray photography from 2008 to 2010,and the relevant information was also recorded.The differences of the mean ESDs among different grade hospitals,equipment types and photographic parameters were statistically analyzed.Results The arithmetic mean of the ESDs for adults undergoing examination of PA chest X-ray photography in Shanghai was 0.23 mGy,and the 75th percentile value was 0.29 mGy,which were all below the current China diagnostic reference level (0.40 mGy).The averaged ESDs were significantly correlated with the grade of hospital,the equipment types and the photographic parameters.Conclusions Compared with the value in the last century,the ESD for adults undergoing PA chest X-ray photography in Shanghai obviously decreases,and there are the potentials for further reduction.

Objective To develop a new software system that cau directly display the predicted results on an electronic map,in order to get a directly perceived understanding of the affected areas of nuclear and radiological terrorism events in city areas.Methods Three scenarios of events including spreading radioactive materials, dirty bomb attack,and explosion or arson attacks on the radiation facilities were assumed.Gaussian diffusion model was employed to predict the spread and deposition of radioactive pollutants,and both the internal and external doses were estimated for the representative person by using the corresponding dose conversion factors.Through integration of the computing system and Mapinfo geographic information system(GIS),the predicted results were visually displayed on the electronic maps of a city.Results The new software system could visually display the predicted results on the electronic map of a city, and the predicted results were consistent with those calculated by the similar software Hotspot(R)The deviation between this system and Hotspot was less than 0.2 km for predicted isoplethic curves of dose rate downwind.Conclusions The newly developed software system is of the practical value in predicting the effects of nuclear and radiological terrorism events in city areas.

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.

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 investigate the methods and effects of abdominal and pelvic shielding for pediatric chest CT examinations.Methods The 705-D phantom made by Computerized Imaging Reference Systems (CIRS) was used to replace a 5-year-old child,thermoluminescent dosimeters were set in the abdomen and pelvis to measure the organ and tissue doses.Chest scans were conducted with the routine protocol for pediatric chest CT examinations.Doses to main organs and tissues in the abdomen and pelvis were measured after chest CT scans without lead apron,with lead apron covering anterior of the abdomen and pelvis and with apron wrapping same part,respectively.Results Absorbed doses to some abdominal organs near the irradiation field were up to several mGy in a procedure of pediatric chest CT examination.There were statistically significant differences among the dose values for three different scans at the same location (x2 =16.00,P ＜ 0.05).Statistically significant difference was also found between the dose values for scans,which were measured with wrapping and covering approaches (Z =-2.52,P ＜ 0.05).Compared to the doses in the condition of no shielding,the doses in testis and colon reduced by 71.2％ and 42.3％,respectively,if the abdomen and pelvis was wrapped with a lead apron (0.35 mm Pb),and reduced by 55.9％ and 26.1％,respectively,if the same lead apron was used to cover the anterior of the abdomen and pelvis.Conclusions In pediatric chest CT examinations,the use of a lead apron can effectively shield the abdomen and pelvis,and plays an important role in protection of the gonad and colon.The wrapping measure is worth being recommended.

Objective To establish an accurate method for estimating the indoor gamma dose rate from decorative stones.Methods Combining a room model with decorating conditions,the gamma dose rates and dose rate conversion factors (DCF) at 1 m above the floor in the room center were calculated with the Monte Carlo simulations,and the calculation results were verified through experiments.Based on the results,the limit of radionuclide contents in stone materials was further discussed.Results The DCF increases with the increase of area or thickness of decorative stones in the same room.The increase of DCF with the thickness of decorative stone is approximately linear.The DCF also increases with the area of decorative stones,but the increasing trend slows down.For the same decorative stones,the smaller the room,the larger the increase of gamma dose rate.Experimental results were consistent with the simulation results within ± 20％.Conclusions The increase of indoor gamma dose rate depends not only on the radionuclide contents,but also on the area and thickness of the decorative stones as well as the room size.The method used in this study can be used to estimate,more accurately than ever,the additional external exposure to residents due to decorative stones,and it provides a theoretical basis for revising the limit standard on radionuclide contents in decorative materials.

Objective To evaluate the influence of indoor air filtration by air purifier on the behavior of indoor radon progeny and estimate its effects on indoor radon exposure to residents.Methods The concentrations of indoor radon progeny with and without the air filtration were calculated by the theoretical model developed in this study.Based on the dose conversion factors of attached and unattached radon progeny,the mitigation effects of indoor radon exposure due to the air filtration were estimated.Verification experiments were conducted in an airtight room.Results With the air filtration rate increased,the removal efficiency of indoor radon progeny would appear more obvious.For an airtight room with its initial aerosol concentration of 10 000 cm-3,the concentration of total radon progeny would decrease by more than 90％ when the air filtration rate exceeded 10 h-1.But the concentrations of indoor unattached radon progeny would increase by using the air purifier in different extents.The variations of radon progeny concentrations and the decrease of internal doses were closely related to the filtration rate of air purifier.With the air filtration rates increased,the mitigation effects would be better and faster.The internal dose would reduce by more than 70％ when the filtration rate exceeded 5 h-1.Conclusions Although the indoor concentration of unattached radon progeny will increase by using the air purifier,it is still effective in reducing the exposure dose to residents due to the inhalation of radon progeny.

Objective To investigate the feasibility and plan quality of the image-guided volumetric modulated arc therapy (VMAT) based voluntary deep exhale breath-holding technique in the stereotactic ablative body radiotherapy (SABR) for liver tumors.Methods Fifteen patients with liver tumors were involved in this study.All patients were immobilized with voluntary deep exhale breath hold (vDEBH) combined with real-time position management (RPM) respiratory gating system.Treatment was planned using VMAT with 2 modified partial arc and re-planned using intensity modulated radiation therapy (IMRT) technique for comparison.Dosimetric parameters were calculated for plan quality assessment.Quality assurance studies included absolute dose and multiple planar dose verifications,total monitor units and delivery time analysis.Daily cone beam computed tomography imaging was used to verify the motions.Results There were no significant dosimetric differences between VMAT and conventional IMRT plans (P ＞0.05).Both techniques were able to minimize doses to organs at risk including normal liver,kidneys,spinal cord,and stomach.However,the average monitor units with VMAT were significantly lower 28.1％ than those with IMRT(t =3.064,P ＜0.05).The average beam-on time in VMAT plans was 31.6％ shorter than that in IMRT plans(t =2.278,P ＜ 0.05).Conclusions The utilization of VMAT in the treatment planning of SABR for liver tumors under breath control mode has better dosimetrics.In comparison to conventional IMRT plans,VMAT plans have higher efficiency and feasibility.