Patient and occupational dose in neurointerventional procedures

Neurointerventional procedures can involve very high doses of radiation to the patient. Our purpose was to quantify the exposure of patients and workers during such procedures, and to use the data for optimisation. We monitored the coiling of 27 aneurysms, and embolisation of four arteriovenous malformations. We measured entrance doses at the skull of the patient using thermoluminescent dosemeters. An observer logged the dose-area product (DAP), fluoroscopy time and characteristics of the digital angiographic and fluoroscopic projections. We also measured entrance doses to the workers at the glabella, neck, arms, hands and legs. The highest patient entrance dose was 2.3 Gy, the average maximum entrance dose 0.9+/-0.5 Gy. The effective dose to the patient was estimated as 14.0+/-8.1 mSv. Other average values were: DAP 228+/-131 Gy cm(2), fluoroscopy time 34.8+/-12.6 min, number of angiographic series 19.3+/-9.4 and number of frames 267+/-143. The highest operator entrance dose was observed on the left leg (235+/-174 microGy). The effective dose to the operator, wearing a 0.35 mm lead equivalent apron, was 6.7+/-4.6 microSv. Thus, even the highest patient entrance dose was in the lower part of the range in which nonstochastic effects might arise. Nevertheless, we are trying to reduce patient exposure by optimising machine settings and clinical protocols, and by informing the operator when the total DAP reaches a defined threshold. The contribution of neurointerventional procedures to occupational dose was very small.     

Radiation dose quantities and risk in neonates in a special care baby unit

Radiographs are taken in the neonatal period most commonly to assist in the diagnosis and management of respiratory difficulties. Frequent accurate radiographic assessment is required and a knowledge of the radiation dose is necessary to justify such exposures. A survey of radiation doses to neonates from diagnostic radiography (chest and abdomen) has been carried out in the special care baby unit of the Royal Free Hospital. Entrance surface dose (ESD) was calculated from quality control measurements on the X-ray unit itself. Direct measurement of radiation doses was also performed using highly sensitive thermoluminescent dosemeters (TLDs) (LiF:Mg,Cu,P), calibrated and tested for consistency in sensitivity. ESD, as calculated from exposure parameters, was found to range from 28 microGy to 58 microGy, with a mean ESD per radiograph of 36+/-6 microGy averaged over 95 examinations. ESDs as derived from TLD crystals ranged from 18 microGy to 58 microGy for 30 radiographic examinations. The mean energy imparted, the mean whole body dose per radiograph and the mean effective dose were estimated to be 14+/-8 microJ, 10+/-4 microGy and 8+/-2 microSv, respectively. Assuming that neonates and fetuses are equally susceptible to carcinogenic effects of radiation, which involve an overestimation of risk, the radiation risk of childhood cancer from a single radiograph was estimated to be of the order (0.3-1.3) x 10(-6). Radiation doses compared favourably with the reference values of 80 microGy ESD published by the Commission of the European Communities in 1996, and 50 microGy published by the National Radiological Protection Board in 2000.     

Method of patient dose evaluation in the angiographic and interventional radiology procedures

PURPOSE: The aim of this study was to evaluate the effective dose in interventional radiology and angiography procedures on the basis of the dose-area product (DAP), either measured or calculated using two different methods. MATERIALS AND METHODS: We studied 2072 examinations carried out on several X-ray systems both in angiography and in interventional radiology. Some of the systems were equipped with an on-board transmission chamber for DAP measurements; for these systems we took direct DAP measurements for each type of examination. For the systems without the dose measurement device, we used a portable transmission chamber, acquiring the data from a set of sampling frames. We then derived the dose values from the systems' dosimetry data and the information about each examination. To this end, the dosimetry of each x-ray system was done by measuring tube output in the different acquisition modes, backscatter factor and field-homogeneity factor. Survey data sheets were filled in after every examination indicating the exposure data (mean Kv, mAs, focus-skin distance and field size). These values combined with the dosimetric data were used to evaluate the DAP for each exam. Where possible, we compared the measured and calculated DAP values by assessing the percentage deviation between each pair of values. A similar comparison was made for the single examinations using a simplified calculation algorithm reported in the literature. For all the examinations for which we had adequate survey data sheets, we estimated the DAP and the entrance dose values and, with the aid of WinODS software, the effective dose. RESULTS: The direct measurements of DAP showed that, in interventional radiology and angiographic procedures, the variability in examination conditions leads to a wide range of possible patient doses even within the same examination type.The comparison between the measured and calculated DAP using our algorithm showed substantial agreement (mean difference 30%, maximum 80%). By contrast, using the algorithm proposed in the literature, we obtained deviations higher than 100%.An estimate of the effective dose for all the recorded examinations (2072) permitted evaluation of both magnitude and variability of patient doses in special radiology procedures such as angiography and interventional radiology. However, it should be noted that evaluations based on calculated DAP values may be as uncertain as those estimated for DAP, and that clearly the evaluations made for the examinations for which direct measurements are available are more accurate.In particularly 'invasive' examinations in terms of entrance dose, where the threshold limits for deterministic effects might possibly be exceeded, the equivalent doses to critical organs were also assessed. This analysis showed that in a small percentage of patients (5%) 2 Gy to the skin was exceeded in the areas exposed with possible transient erythema, while in fewer than 2% of patients, the 3 Gy limit for temporary epilation was exceeded. CONCLUSIONS: Many interventional radiology, especially haemodynamic, examinations have shown to give significant exposure to patients. The direct dose measurement method has shown to be the only method able to provide reliable information on such exposure.However, the authors believe that since the patient dose cannot be established in advance, even in terms of magnitude and since direct dose measurement cannot be performed on all patients, it is nonetheless interesting to be able to assess, at least semiqualitatively, the amount of the above doses.     

Chest radiography with a digital flat-panel detector: experimental receiver operating characteristic analysis

PURPOSE: To evaluate the influence of different detector radiation doses and peak kilovoltage settings on diagnostic performance and radiation dose at posteroanterior (PA) chest radiography performed with an amorphous silicon flat-panel detector (FPD). MATERIALS AND METHODS: All examinations were performed by using a digital FPD. PA chest radiographs of an anthropomorphic chest phantom were obtained with detector radiation doses of 2.50 microGy (system speed, 400), 1.56 microGy (speed, 640), and 1.25 microGy (speed, 800) and with peak kilovoltage values of 100, 120, and 140 kVp. Four types of simulated lesions-nodules of different sizes, polylobulated lesions, interstitial-nodular lesions, and interstitial-reticular lesions-were superimposed on the phantom. After four radiologists assessed all of the images, receiver operating characteristics analysis was performed. In addition, the entrance surface dose was measured and the effective dose was calculated. RESULTS: Reduced detector dose led to significantly decreased diagnostic performance in overall lesion detection (P <.05). However, over pulmonary areas only, this effect could not be seen. With use of the same kilovoltage values, reducing the detector dose, even to 1.25 microGy (speed, 800), did not lead to significantly decreased lesion detectability. In terms of diagnostic performance and effective dose, 120 kVp was the most effective. CONCLUSION: Standard PA chest radiographs should still be acquired at a detector dose of 2.50 microGy (speed, 400) with 120 kVp to yield the highest diagnostic performance. However, when the present analysis was focused on the lung fields only, no significant loss in diagnostic performance could be demonstrated, even after a 50% reduction in radiation dose.     

Comparison of effective doses obtained from dose-area product and air kerma measurements in interventional radiology

In this study, measurements of dose-area product (DAP) and entrance dose were carried out simultaneously in a sample of 162 adult patients who underwent different interventional examinations. Effective doses for each measurement technique were estimated using the conversion factors that have been determined for specific X-ray views in a mathematical phantom. Exposure conditions used in clinical practice never match these theoretical models exactly, and deviations from the assumed standard conditions cause uncertainties in effective dose estimations. Higher effective dose values are found if the air kerma results are used rather than DAP readings, both for patient and Rando phantom studies. Comparison of DAP, fluoroscopy times and skin doses were made with published data. DAP measurement for the effective dose calculation and thermoluminescent dosimeter for the skin dose estimates are found to be the most reliable methods for patient dosimetry.     

Estimation of the effective dose of patient in interventional radiology: study of coronary angiography

The applications of interventional radiology (IVR) increasingly are being used in clinical examinations, where they tend to extend examination time. In addition, the risk of occupational exposure necessarily is increasing with this technology. In this study, the dose distributions in a sliced acrylic-acid phantom involving the bore for each irradiation condition were measured using a thermoluminescence dosimeter (TLD). Four patterns of set-up for the fluoroscopy unit were chosen as references for the conditions generally used clinically. Exposure also was measured with dose area product (DAP), and we then calculated the entrance skin dose and effective dose for the patient. The results showed that the effective dose was 7.0 mSv to 8.0 mSv at LAO45 degrees and RAO30 degrees; 100 kV, 2.3 mSv to 3.3 mSv at LAO45 degrees and RAO30 degrees; 80 kV. The effective dose is greatly influenced by the setup of fluoroscopy in IVR. The change in DAP is especially influenced. We found that the relation between DAP and effective dose was corrected with the exponential function. The effective doses were not necessarily less than those of other radiation examinations, and increase. When PCI and TAE are repeated many times in IVR, we propose that the effective dose should be taken into consideration together with the skin dose for dose control management.     

Radiation exposure to premature infants in a neonatal intensive care unit in Turkey

OBJECTIVE: The aim of this work was to determine the radiation dose received by infants from radiographic exposure and the contribution from scatter radiation due to radiographic exposure of other infants in the same room. MATERIALS AND METHODS: We retrospectively evaluated the entrance skin doses (ESDs) and effective doses of 23 infants with a gestational age as low as 28 weeks. ESDs were determined from tube output measurements (ESD(TO)) (n = 23) and from the use of thermoluminescent dosimetry (ESD(TLD)) (n = 16). Scattered radiation was evaluated using a 5 cm Perspex phantom. Effective doses were estimated from ESD(TO) by Monte Carlo computed software and radiation risks were estimated from the effective dose. ESD(TO) and ESD(TLD) were correlated using linear regression analysis. RESULTS: The mean ESD(TO) for the chest and abdomen were 67 microGy and 65 microGy per procedure, respectively. The mean ESD(TLD) per radiograph was 70 microGy. The measured scattered radiation range at a 2 m distance from the neonatal intensive care unit (NICU) was (11-17 microGy) per radiograph. Mean effective doses were 16 and 27 microSv per procedure for the chest and abdomen, respectively. ESD(TLD) was well correlated with ESD(TO) obtained from the total chest and abdomen radiographs for each infant (R(2) = 0.86). The radiation risks for childhood cancer estimated from the effective dose were 0.4 x 10(-6) to 2 x 10(-6) and 0.6 x 10(-6) to 2.9 x 10(-6) for chest and abdomen radiographs, respectively. CONCLUSION: The results of our study show that neonates received acceptable doses from common radiological examinations. Although the contribution of scatter radiation to the neonatal dose is low, considering the sensitivity of the neonates to radiation, further protective action was performed by increasing the distance of the infants from each other.     

The effect of a picture archiving and communication system (PACS) on patient radiation doses for examination of the lateral lumbar spine

This study was conducted to determine whether the doses for the radiographic examination of the lateral lumbar spine changed as a result of the introduction of a hospital-wide picture archiving and communication system (PACS). Doses were measured by thermoluminescent dosimeters (TLD) and dose-area product (DAP) meter readings for 100 patient examinations using a 300-speed conventional film/screen system and for 96 patient examinations when PACS was fully operational. Radiographic technique, exposure factors and patient characteristics were noted and effective doses were calculated, and a comparison was made of all variables. No significant differences between conventional and PACS working were found in surface entry and effective doses for single views of the lateral lumbar spine, but there was a 20% reduction in DAP readings with PACS. However, when summed doses for all images, including rejects, required to demonstrate the lateral lumbar spine for each patient were compared, PACS was found to be associated with significantly lower surface entry (TLD) dose, DAP reading and effective dose (28%, 36% and 16%, respectively) than conventional film. For single images of L1-5, when PACS was in use, there was a significant reduction in the DAP readings and increases in the area of the film/plate irradiated, the focus-to-skin distance and the focus-to-film distance. In addition, significantly fewer lumbosacral junction views were undertaken when PACS was in use. Since many confounding factors may have influenced the results over the period of dose measurement, regression models were used to determine the significance of PACS. These models showed that the use of PACS was not significant in causing any differences in the dose for single images as compared with when film was used, but was significant in the resulting total dose reductions for the examinations.     

Calculating effective dose on a cone beam computed tomography device: 3D Accuitomo and 3D Accuitomo FPD

OBJECTIVES: This study evaluates two methods for calculating effective dose, CT dose index (CTDI) and dose-area product (DAP) for a cone beam CT (CBCT) device: 3D Accuitomo at field size 30x40 mm and 3D Accuitomo FPD at field sizes 40x40 mm and 60x60 mm. Furthermore, the effective dose of three commonly used examinations in dental radiology was determined. METHODS: CTDI(100) measurements were performed in a CT head dose phantom with a pencil ionization chamber connected to an electrometer. The rotation centre was placed in the centre of the phantom and also, to simulate a patient examination, in the upper left cuspid region. The DAP value was determined with a plane-parallel transmission ionization chamber connected to an electrometer. A conversion factor of 0.08 mSv per Gy cm(2) was used to determine the effective dose from DAP values. Based on data from 90 patient examinations, DAP and effective dose were determined. RESULTS: CTDI(100) measurements showed an asymmetric dose distribution in the phantom when simulating a patient examination. Hence a correct value of CTDI(w) could not be calculated. The DAP value increased with higher tube current and tube voltage values. The DAP value was also proportional to the field size. The effective dose was found to be 11-77 microSv for the specific examinations. CONCLUSIONS: DAP measurement was found to be the best method for determining effective dose for the Accuitomo. Determination of specific conversion factors in dental radiology must, however, be further developed.     

Patient radiation dose at CT urography and conventional urography

PURPOSE: To measure and compare patient radiation dose from computed tomographic (CT) urography and conventional urography and to compare these doses with dose estimates determined from phantom measurements. MATERIALS AND METHODS: Patient skin doses were determined by placing a thermoluminescent dosimeter (TLD) strip (six TLD chips) on the abdomen of eight patients examined with CT urography and 11 patients examined with conventional urography. CT urography group consisted of two women and six men (mean age, 55.5 years), and conventional urography group consisted of six women and five men (mean age, 58.9 years). CT urography protocol included three volumetric acquisitions of the abdomen and pelvis. Conventional urography protocol consisted of acquisition of several images involving full nephrotomography and oblique projections. Mean and SD of measured patient doses were compared with corresponding calculated doses and with dose measured on a Lucite pelvic-torso phantom. Correlation coefficient (R(2)) was calculated to compare measured and calculated skin doses for conventional urography examination, and two-tailed P value significance test was used to evaluate variation in effective dose with patient size. Radiation risk was calculated from effective dose estimates. RESULTS: Mean patient skin doses for CT urography measured with TLD strips and calculated from phantom data (CT dose index) were 56.3 mGy +/- 11.5 and 54.6 mGy +/- 4.1, respectively. Mean patient skin doses for conventional urography measured with TLD strips and calculated as entrance skin dose were 151 mGy +/- 90 and 145 mGy +/- 76, respectively. Correlation coefficient between measured and calculated skin doses for conventional urography examinations was 0.95. Mean effective dose estimates for CT urography and conventional urography were 14.8 mSv +/- 90.0 and 9.7 mSv +/- 3.0, respectively. Mean effective doses estimated for the pelvic-torso phantom were 15.9 mSv (CT urography) and 7.8 mSv (conventional urography). CONCLUSION: Standard protocol for CT urography led to higher mean effective dose, approximately 1.5 times the radiation risk for conventional urography. Patient dose estimates should be taken into consideration when imaging protocols are established for CT urography.     

Radiation burden to paediatric patients due to micturating cystourethrography examinations in a Dutch children's hospital

Micturating cystourethrography (MCU) examinations of paediatric patients in a major Dutch children's hospital (JKZ) were evaluated to generate quantitative information on effective dose (E). A standard examination involves three radiographs plus fluoroscopy. Observed total dose-area product (DAP) for 84 children increased, on average, with increasing age class from 0.2 to 2.2 Gy cm2. In 11 cases, separate DAP per view was measured; enabling determination, per view, of organ (CF) and effective (CE) dose conversion factors, i.e. dose per unit of DAP. Monte Carlo simulation of photon transport in male and female mathematical phantoms was applied for newborn, 1 year, 5 year, 10 year and 15-year-old patients, and interpolated for other ages. CE per view decreases with increasing age class, yielding about a factor of 10 difference between the extremes of the range. Female values are usually some 20-30% above male ones. CE for one of the views appeared to be representative for the complete examination and was used to estimate total E for each patient. Averaged per age class, E remains approximately constant at 0.3-0.4 mSv, although a tendency to increase with increasing age exists, for females in particular. Within an age class, individual patients may differ in E by a factor of two up to six. Stomach, lower large intestine, bladder wall, liver and ovaries receive relatively high doses. Compared with published data and DAP measured in a few other Dutch hospitals, the radiation burden of MCU is low at the JKZ. This indicates a good degree of optimization with respect to radiation protection (e.g. modern equipment, increased tube voltage, fast film-screen combination).     

Measurement of dose in panoramic dental radiology

The National Radiological Protection Board (NRPB) has recommended the introduction of dose-width product (DWP) for the measurement of patient dose in panoramic dental radiology and has proposed a reference level of 65 mGy mm for adult exposures. This paper describes a method for measuring DWP and dose-area product (DAP) using thermoluminescent dosemeters (TLDs). The technique was used on 16 sets with a range of exposure settings. The mean value of DWP was 14% higher than the mean value reported from a survey by the NRPB. This difference is most likely to be caused by systematic variations due to measurement method. The average DAP for a standard adult examination was shown to be 11.3 cGy cm2. Data are presented so that the DAP can be derived from the exposure factors (tube current and operating potential) and beam area. Based on published data for effective dose, it is estimated that the DAP to effective dose conversion factor is approximately 0.06 mSv(Gy cm2)-1. The average DAP value (11.3 cGy cm2) can be compared with the average value for intraoral radiography (9.3 cGy cm2) based on the NRPB survey of entrance surface doses assuming 6 cm circular collimation.     

Cumulative patient effective dose in cardiology

Medical radiation from X-rays and nuclear medicine is the largest non-natural (man-made) source of radiation exposure in Western countries. The aim of this study was to assess the individual cumulative effective dose in patients admitted to our cardiology ward. We collected a cumulative radiological history from a structured questionnaire and access to hospital records in 50 consecutive adult patients (36 males; age, 66.7+/-10.8 years) admitted to the Institute of Clinical Physiology in Pisa. The cumulative effective dose was assessed as an indicator of stochastic risk of cancer. We derived the effective dose for each individual examination from the Medical Imaging Guidelines of the European Commission (2001). On average, each patient underwent a median of 36 examinations (interquartile range, 23-46). The median cumulative effective dose was 60.6 mSv. Three types of procedures were responsible for approximately 86% of the total collective effective dose: (i) arteriography and interventional cardiology (12% of examinations, 48% of average dose per patient); (ii) nuclear medicine (5% of examinations, 21% of average dose per patient); and (iii) CT (4% of examinations, 17% of average dose per patient). The median estimated extra risk of cancer was approximately 1 in 200 exposed subjects. In conclusion, the average contemporary cardiological patient is exposed to a significant cumulative effective dose from diagnostic and therapeutic interventions. It is important to log cumulative dose for each patient at the time of each examination. Every effort should be made to justify the indications and to optimize the doses.     

Radiation doses to paediatric patients up to 5 years of age undergoing micturating cystourethrography examinations and its dependence on patient age: a Monte Carlo study

The effective dose received by children up to 5 years of age from micturating cystourethrography (MCU) examinations was estimated in this study. The MCU examination consisted of 5 radiological views, 2 anteroposterior (AP) and three oblique (OBL) views. Entrance surface doses (ESD) were measured with thermoluminescent dosimeters for 30 children. The average ESD values per view varied from 0.34 mGy up to 0.57 mGy. In order to calculate the organ and effective doses, Monte Carlo MCNP-4A radiation transport simulation code was used. It was applied to three mathematical phantoms representing newborn, 1 and 5 year old children and all the patients were classified in those three groups. The effective dose conversion factors (C(f)) were calculated as the ratio of effective dose over the entrance dose. The C(f) factors decrease as the children's age increases. Children simulated by a newborn mathematical phantom, had C(f) factors almost double those represented by a 1-year-old mathematical phantom. For children simulated by a 5 year old phantom, the C(f) factors for AP and OBL views were almost the same. This was true for both male and female patients. The mean effective dose per view for male and female patients was found to be E=0.16 mSv. The effective dose per examination for male patients was E=0.86+/-0.31 mSv and E=0.76+/-0.28 mSv for female patients.     

Diagnostic image quality of mobile neonatal chest X-rays and the radiation exposure incurred.

A study was undertaken to identify the variation of entrance skin doses (ESDs) in mobile neonatal chest radiography with regard to the European Commission (EC) reference dose and to examine potential relationships with image quality and radiographic techniques. Five sites from the former North West Thames region participated. All mobile neonatal radiographic techniques were surveyed. Dose-area product per examination was directly measured and the ESD calculated. Image quality criteria were developed from those published by the EC. Image quality was graded by two independent observers. Over the five sites, 144 examinations were recorded. Calculated ESDs ranged up to 160 microGy, with an appreciable variation not only between sites but also within sites. A clear relationship between actual rather than nominal speed and dose over all sites was demonstrated (r = -0.95, p = 0.013). No correlation between image quality and dose was noted (r = -0.044, p = 0.665). Neonatal imaging systems at participating sites, within the North Thames region, comply with EC guidelines on patient dose and image quality for mobile chest X-rays. Significant variation in ESDs was encountered between sites with no discernible relationship with image quality or the employed radiographic techniques as described by the EC. The strong inverse relationship between ESDs and actual rather than nominal speed suggests a neglected aspect of radiation protection.     

Occupational radiation exposure from fluoroscopically guided percutaneous transhepatic biliary procedures

PURPOSE: The aim of this study was to determine occupational dose levels for projections commonly used in fluoroscopically guided percutaneous transhepatic biliary (PTB) drainage and stent placement procedures. METHODS: Exposure data from 71 consecutive PTB examinations were analyzed to determine average examination parameters for biliary drainage and stent placement procedures. An anthropomorphic phantom was exposed at three projections common in PTB interventions according to the actual geometric parameters recorded in the patient study. Scattered air-kerma dose rates were measured for neck, waist, and gonad levels at various sites in the interventional radiology laboratory. To produce technique- and instrumentation-independent data, dose rate values were converted to dose-area product (DAP)-normalized air-kerma values. In addition, sets of thermoluminescent dosimetry crystals were placed in both hands of the interventional radiologist to monitor doses during all PTB procedures. RESULTS: Isodose maps of DAP-normalized air-kerma doses in the interventional laboratory for projections commonly used in PTB procedures are presented. To facilitate effective dose estimation, normalized dosimetric data at the interventional radiologist's position are presented for left and right access drainage procedures, metallic stent placement only, and drainage and metallic stent placement in one-session procedures with and without under-couch shielding. Doses to the hands of interventional radiologists are presented for left and right transhepatic biliary access and metallic stent placement. CONCLUSIONS: Body level-specific normalized air-kerma distributions from commonly used projections in PTB procedures may be useful to accurately quantify dose, maximum workloads, and possible radiogenic risks delivered to medical personnel working in the interventional radiology laboratory. Normalized dose data presented will enable occupational exposure estimation from other institutions.     

Comparison of radiation doses to patients undergoing standard radiographic examinations with conventional screen-film radiography, computed radiography and direct digital radiography

New flat-panel direct digital radiography equipment has recently been installed in our Accident and Emergency Department; its characteristics and versatility are well suited to the work undertaken in this environment. The aim of this study was to compare radiation doses to patients undergoing standard radiographic examinations using conventional screen-film radiography, computed radiography and direct digital radiography; entrance surface dose and effective dose were calculated for six standard examinations (a total of 10 projections) using standard patient exposure parameters for the three imaging modalities. It was found that doses for computed radiography (all examinations) were higher than the doses for the other two modalities; effective doses for direct digital radiography were approximately 29% and approximately 43% lower than those for screen-film radiography and computed radiography, respectively. The image quality met the criteria in the European guidelines for all modalities.     

直接摄影检查患者的照射剂量分析

目的 通过对不同部位直接摄影(DR)检查的医学数字成像和传输(DICOM)文件信息中的患者剂量信息的统计,调查不同投照部位DR摄片的照射剂量分布范围,分析影响DR检查照射剂量的因素。方法 随机选取浙江省某三甲医院2009年1月至4月5160次DR摄片,包括胸部、胸椎及腰椎正、侧位、腹部前后位及骨盆正位。应用软件自动提取每例患者检查中DICOM信息文件中的剂量面积乘积(DAP),并结合照射野的范围,计算各部位DR检查的入射表面剂量(ESD)。结果 腹部前后位、腰椎侧位、胸椎正侧位的变异系数在60%以下;胸部正侧位、腰椎正位、骨盆正位的变异系数为60%~80%。各个部位的DAP最大值与最小值比值,除腹部前后位较小为3倍,其余部位差异较大。其中,腰椎正位最大差别为46倍、腰椎侧位30倍,胸椎侧位、胸部正位、侧位、骨盆正位、胸椎正位分别为23、23、18、16、11倍。通过计算得到ESD值选择75%分位点与现行普通摄片诊断参考水平(DRL)比较后发现,胸部正、侧位分别下降75%和73%;腰椎正侧位下降66%和77%;胸椎正侧位下降85%和84%;骨盆正位下降88%;腹部前后位下降88%。结论 DR检查中各个部位的DAP与ESD值存在较大变动,ESD值与现行的常规摄片的DRL相比有较大下降;有必要回顾分析DR摄片的患者照射剂量,对患者照射剂量与图像质量进行质量管理。     

The effect of beam tube potential variation on gonad dose to patients during chest radiography investigated using high sensitivity LiF:Mg,Cu,P thermoluminescent dosemeters

Optimization of X-ray beam tube potential (kVp) in radiological examinations can minimize patient dose. This research aims to investigate the effect of tube potential variation on gonad doses to patients during posteroanterior (PA) chest radiography examinations. This study was carried out using a Toshiba general purpose X-ray unit and a Rando phantom. Dose measuring equipment included an ion chamber system, a dose-area product (DAP) meter and a thermoluminescent dosemeter (TLD) reader system with high sensitivity TLD pellets of LiF:Mg,Cu,P for low level gonad dose measurement. PA chest exposures of the phantom to produce a constant exit dose were made using a standard low tube potential (range 60-100 kVp) non-grid technique and a high tube potential (range 95-150 kVp) grid technique. Entrance surface doses (ESDs) and DAPs were also included in the measurements. Effective doses (EDs) were computed from ESD and DAP measurements using NRPB-SR262 and Xdose software. Results show that with the low tube potential technique both ovary dose and testes dose increase with increasing tube potential; statistically significant correlations of r = 0.994 (p = 0.0006) and r = 0.998 (p = 0.001), respectively, were found. For both organs, doses increase at a rate of approximately 2% per kVp. With the high tube potential technique there is insignificant correlation between gonad doses and tube potential. When comparing patient doses from typical exposures made at 70 kVp (low tube potential non-grid technique) with doses from exposures made at 120 kVp (high tube potential grid technique), the high tube potential technique delivers significantly higher values for ESD, and ovary, testes and effective doses by factors of 1.7, 5.2, 5.5 and 2.7, respectively.     

Radiation doses to patients undergoing scoliosis radiography

In this study we computed the radiation doses associated with scoliosis radiography and investigated how these radiation doses are influenced by the weight of the patient. We recorded the radiographic technique factors of 61 consecutive patients (46 females and 15 males) undergoing scoliosis radiography. A wedge-shaped aluminium filter attenuated the X-ray beam in the "chest region" relative to the "abdomen region". X-ray tube air kerma output factors (microGy mAs-1) and half value layers (HVLs) were determined experimentally for the "chest region" and "abdomen region". The energy imparted to each patient was computed from the air kerma area product, X-ray beam HVL and measured patient thickness. Values of patient effective dose were obtained using effective dose-to-energy conversion factors for specified radiographic projections, taking into account each patient's weight. The median patient age was 17 years, and the median patient weight was 53 kg. Entrance skin air kerma values in the "chest region" were approximately a factor of four lower than those in the "abdomen region". The air kerma values increased by a factor of two when the patient weight increased from 30 kg to 70 kg. Approximately 80% of the total energy imparted to a patient undergoing a scoliosis examination was in the "abdomen region", with the remaining 20% imparted to the "chest region". Energy imparted increased with patient weight, and was approximately 3 mJ for a 30 kg patient and approximately 8 mJ for a 70 kg adult patient. Effective doses showed little correlation with patient weight, with an average-sized patient (50 kg) receiving an effective dose of approximately 140 microSv. Patients undergoing scoliosis radiography receive effective doses that are low in comparison with other types of radiographic examination.