Entrance Surface Dose Measurements Research Articles

Doses to patients in some routine diagnostic X-ray examinations in Iran: proposed the first Iranian diagnostic reference levels

The national diagnostic reference levels (NDRLs) form an efficient, concise and powerful standard for optimising the radiation protection of a patient. With an aim to establish the first Iranian NDRLs, the nationwide survey of the frequency of medical X-ray examinations and entrance surface doses received by the patients during the most typical X-ray examinations has been performed. Seven most common X-ray examinations in 14 projections were included in the list of procedures under consideration. Hospitals of different sizes and levels using different X-ray machines were represented in the survey. The standard thermoluminescence dosimeters were applied to measure entrance surface dose (ESD). A total of 1601 patients were included in this study. The data were analysed statistically, and the minimum, median, mean, maximum, first and third quartile values of ESDs are reported. Finally, the proposed Iranian DRLs are compared with the international reference dose values reported by the European Commission, the International Atomic Energy Agency and the National Radiological Protection Board.

National reference doses for common radiographic, fluoroscopic and dental X-ray examinations in the UK

The National Patient Dose Database (NPDD) is maintained by the Radiation Protection Division of the Health Protection Agency. The latest review of the database analysed the data collected from 316 hospitals over a 5-year period to the end of 2005. The information supplied amounted to a total of 23 000 entrance surface dose measurements and 57 000 dose-area product measurements for single radiographs, and 208 000 dose-area product measurements along with 187 000 fluoroscopy times for diagnostic examinations or interventional procedures. In addition, patient dose data for dental X-ray examinations were included for the first time in the series of 5-yearly reviews. This article presents a summary of a key output from the NPDD - national reference doses. These are based on the third quartile values of the dose distributions for 30 types of diagnostic X-ray examination and 8 types of interventional procedure on adults, and for 4 types of X-ray examination on children. The reference doses are approximately 16% lower than the corresponding values in the previous (2000) review, and are typically less than half the values of the original UK national reference doses that were derived from a survey in the mid-1980s. This commentary suggests that two of the national reference doses from the 2000 review be retained as diagnostic reference levels because the older sample size was larger than for the 2005 review. No clear evidence could be found for the use of digital imaging equipment having a significant effect on dose.

Entrance surface dose measurements in pediatric radiological examinations

A survey of pediatric radiological examinations was carried out in a reference pediatric hospital of the city of São Paulo, in order to investigate the doses to children undergoing conventional X-ray examinations. The results showed that the majority of pediatric patients are below 4 years, and that about 80% of the examinations correspond to chest projections. Doses to typical radiological examinations were measured in vivo with thermoluminescent dosimeters (LiF: Mg, Ti and LiF: Mg, Cu, P) attached to the skin of the children to determine entrance surface dose (ESD). Also homogeneous phantoms were used to obtain ESD to younger children, because the technique uses a so small kVp that the dosimeters would produce an artifact image in the patient radiograph. Four kinds of pediatric examinations were investigated: three conventional examinations (chest, skull and abdomen) and a fluoroscopic procedure (barium swallow). Relevant information about kVp and mAs values used in the examinations was collected, and we discuss how these parameters can affect the ESD. The ESD values measured in this work are compared to reference levels published by the European Commission for pediatric patients. The results obtained (third-quartile of the ESD distribution) for chest AP examinations in three age groups were: 0.056 mGy (2–4 years old); 0.068 mGy (5–9 years old); 0.069 mGy (10–15 years old). All of them are below the European reference level (0.100 mGy). ESD values measured to the older age group in skull and abdomen AP radiographs (mean values 3.44 and 1.20 mGy, respectively) are above the European reference levels (1.5 mGy to skull and 1.0 mGy to abdomen). ESD values measured in the barium swallow examination reached 10 mGy in skin regions corresponding to thyroid and esophagus. It was noticed during this survey that some technicians use, improperly, X-ray fluoroscopy in conventional examinations to help them in positioning the patient. The results presented here are a preliminary survey of doses in pediatric radiological examinations and they show that it is necessary to investigate the technical parameters to perform the radiographs, to introduce practices to control pediatric patient's doses and to improve the personnel training to perform a pediatric examination.

Radiation dose optimisation and risk estimation to patients and staff during hysterosalpingography

Hysterosalpingography (HSG) is an efficient radiological examination for the evaluation of the female reproductive tract. However, it involves unavoidable irradiation to the ovaries of women in childbearing age. Therefore, radiation dose optimisation is required in order to reduce the probability of the associated risks. This study attempts to: measure patient and staff doses, estimate the effective dose and radiation risk for HSG using digital fluoroscopic images. Thirty-seven patients with infertility were examined using two digital X-ray machines. Thermoluminescence dosimeters (TLD) were used to measure entrance surface dose (ESD) for patients and staff during the procedure. The mean ESD and thyroid surface dose of the patient were 3.60 and 0.17 mGy, respectively, while the mean ESD for the staff was 0.18 mGy per procedure. The patient overall risk for cancer and hereditary effects is 24 x 10(-6), while the risk for the staff is negligible. HSG with fluoroscopic technique demonstrate improved dose characteristics, compared to the conventional radiographic-based technique, reducing the surface dose by a factor of 3, without compromising the diagnostic findings.

Local diagnostic reference levels for some common diagnostic X-ray examinations in Tehran county of Iran

Various researchers who have carried out national and international surveys have reported wide variations in patient dose arising from specific X-ray examinations. This study was carried out as a part of a comprehensive project to establish national diagnostic reference level (NDRL), for the first time, in Iran. Seven most common X-ray examinations in 11 projections were included. Thermo luminescence dosimeters (TLD-100) were used to measure entrance surface doses (ESDs). The study group consisted of 535 patients who were referred for X-ray examinations to 12 randomly selected public hospitals in Tehran County. Minimum, median, mean, maximum, first and third quartile values of ESDs are reported. Our results are evident that mean dose values of patients undertaking a specific examination are widely different in various hospitals. Wide dose differences may emerge from complex causes, but in general, low peak kilovoltage and high milli Amperes are associated with higher doses. The results of this work together with further data expected to emerge from the work in progress will provide a useful base to establish Iran's DRLs.

Radiation doses in common X-ray examinations carried out in two dedicated paediatric hospitals

In this study, the entrance surface dose (ESD) and the respective effective dose (E) were determined for paediatric patients undergoing various common radiological examinations in two dedicated paediatric hospitals. Measurements of ESD were carried out in 289 examinations using thermoluminescent dosemeters. The patients were categorised according to their age and the mean ESD and E values were determined for each examination and age category. These ESD values were compared with the existing diagnostic reference levels (DRLs). In both hospitals there were cases where the DRLs were exceeded but in one of them this was rather the general rule, since additionally to the routine use of grid and low tube potential settings, occasional use of fluoroscopy for positioning check was also observed. While the remedial actions required to appropriately reduce the doses were clearly identified, this cannot be achieved without the cooperation of medical physicists with operators and radiologists.

Patient and Staff Dosimetry in Vertebroplasty

Eleven vertebroplasty operations were studied in terms of radiation dose. Doses to patients and staff associated with vertebroplasty were measured. Occupational doses were compared with the annual dose limits, and the effectiveness of the used radiation protection means was estimated. Patient dose was estimated by means of both surface and effective dose, and the radiation-induced risk was evaluated. Vertebroplasty is a recent minimally invasive technique for the restoration of vertebral body fractures. It involves fluoroscopic exposure, and so, it demands dose measurements for both patient and staff exposed to radiation. Thermoluminescent dosimeters (TLDs) were placed on the medical personnel and the effective dose was derived. Slow films were placed to patients' skin to measure entrance surface dose. Furthermore, a Rando phantom loaded with TLDs was irradiated under conditions simulating vertebroplasty, in order to estimate effective dose to the patient. Mean fluoroscopy time was 27.7 minutes. Patient's mean skin dose was 688 mGy, while effective dose was calculated to be 34.45 mGy. It was estimated that the primary operator can perform about 150 vertebroplasty operations annually without exceeding the annual dose constraints, whereas occupational dose can be reduced by 76% using mobile shielding. Measures have to be taken to reduce patient's skin dose, which, in extreme cases, may be close to deterministic effects threshold. The highest dose rates, recorded during the procedure, were found for primary operator's hands and chest when no shielding was used.

Radiation risk assessment in neonatal radiographic examinations of the chest and abdomen: a clinical and Monte Carlo dosimetry study

Seeking to assess the radiation risk associated with radiological examinations in neonatal intensive care units, thermo-luminescence dosimetry was used for the measurement of entrance surface dose (ESD) in 44 AP chest and 28 AP combined chest–abdominal exposures of a sample of 60 neonates. The mean values of ESD were found to be equal to 44 ± 16 µGy and 43 ± 19 µGy, respectively. The MCNP-4C2 code with a mathematical phantom simulating a neonate and appropriate x-ray energy spectra were employed for the simulation of the AP chest and AP combined chest–abdominal exposures. Equivalent organ dose per unit ESD and energy imparted per unit ESD calculations are presented in tabular form. Combined with ESD measurements, these calculations yield an effective dose of 10.2 ± 3.7 µSv, regardless of sex, and an imparted energy of 18.5 ± 6.7 µJ for the chest radiograph. The corresponding results for the combined chest–abdominal examination are 14.7 ± 7.6 µSv (males)/17.2 ± 7.6 µSv (females) and 29.7 ± 13.2 µJ. The calculated total risk per radiograph was low, ranging between 1.7 and 2.9 per million neonates, per film, and being slightly higher for females. Results of this study are in good agreement with previous studies, especially in view of the diversity met in the calculation methods.

Radiation doses to patients undergoing standard radiographic examinations: a comparison between two methods

The objective of the study was to derive a mathematical method for calculating the entrance surface dose (ESD) from exposure factors for all tube potentials used in clinical practice and to compare the calculated ESDs (ESD(C)) with those measured (ESD(TLD)) using thermoluminescent dosemeters (TLDs). The exposure parameters of 43 patients who underwent (a) posteroanterior (PA) and lateral (LAT) chest examination (13 patients), (b) supine abdomen (10 patients), (c) erectus abdomen (10 patients), or (d) urinary tract examination (10 patients) were recorded. Patient ESD was directly measured by TLDs and calculated from exposure factors. The differences between ESD(C) and ESD(TLD) were quite small and could be explained by the uncertainties involved in both methods, in all but the PA chest examination where the ESD(C) was about 50% larger than ESD(TLD). However, in PA chest the ESD(TLD) was close to the minimum detectable dose of TLDs, questioning the accuracy of ESD(TLD). Further investigation showed that using the high tube potential technique (130 kV) in the PA chest examination resulted in very short exposure times, in the region of 4 ms. In such short exposure times, the X-ray generator operation presented stability problems that led to loss of output linearity and consequently to false calculation of ESD. The calculation method offers a reliable and cheap alternative to the measurement of ESD by TLD, provided that the exposure times are not as short as in the PA chest examinations recorded in this study, so that the output linearity with tube current-time product (mAs) is maintained.

Pediatric patient surface doses in neuroangiography

Neuroangiographic techniques (diagnostic and interventional) can be lengthy and complex and can be associated with high radiation entrance skin doses from fluoroscopy and digital subtraction angiography (DSA). To measure entrance surface doses received by pediatric patients undergoing neuroangiographic procedures and to (1) compare these doses with thresholds for deterministic effects, (2) compare these doses with those reported in adults, and (3) to understand the dose relationships among diagnostic and interventional procedures, DSA and fluoroscopy. A neurobiplane unit with fluoroscopic and DSA capabilities was used for all neuroangiographic procedures. An automated patient dosimeter, installed on both planes of the unit, calculated maximum surface dose. The dosimeter also recorded the number of angiographic frames and the length of fluoroscopy time for each procedure. This retrospective study analyzed entrance surface doses to 100 pediatric patients, 76 of whom underwent neuroangiographic diagnostic procedures and 24 of whom underwent neuroangiographic interventional procedures. The DSA acquisitions ranged from 44 frames to 1,428 frames per procedure and fluoroscopy times ranged from 1.1 to 85.6 min per procedure. The mean surface dose from fluoroscopy was 68.1 mGy (max: 397.1 mGy) in the frontal (PA) plane; in the lateral (LAT) plane, the mean surface dose was 40.9 mGy (max: 418.5 mGy). The mean surface doses from DSA were 263.1 and 126.9 mGy in the frontal and lateral planes, with maximum doses of 924.4 and 410.1 mGy, respectively. Mean fluoroscopy dose rates were 5.4 mGy/min in the PA plane and 4.7 mGy/min in the LAT plane. The DSA largely contributed to the overall procedural surface dose, accounting for 82% of the combined surface dose in the each of the imaging planes. The surface dose for each procedure measured in this study was found to be below thresholds for deterministic effects. Interventional procedures consistently yield the highest doses.

Conceptus radiation dose assessment from fluoroscopically assisted surgical treatment of hip fractures.

Our aims in the present study were to (a) provide normalized dose data for the estimation of the conceptus dose from fluoroscopically assisted surgical treatment of hip fractures carried out during all trimesters of pregnancy and (b) estimate the conceptus radiation dose and risks associated with fluoroscopy during a typical treatment of hip fracture performed on a pregnant woman. Conceptus doses normalized to entrance surface dose (ESD) or dose area product (DAP) were obtained with the help of anthropomorphic phantoms simulating pregnancy in the three trimesters of gestation. ESD and conceptus dose measurements were carried out using thermoluminescent dosimeters. DAP to conceptus dose conversion factors were estimated for the first, second and third trimesters of gestation. Conceptus dose data normalized to ESD were also estimated to investigate whether these conversion factors may be used for procedures carried out in x-ray units not equipped with a DAP meter. Fluoroscopically assisted surgical treatments were performed in 18 women. The projections involved in these procedures are (a) posteroanterior (PA) and (b) lateral crosstable 45 degrees (LC). Radiation doses for a potential conceptus were estimated by using normalized dose data obtained in phantoms. The results consist of tabulated dose data normalized to DAP or ESD for the estimation of a conceptus dose. An important finding of this study was that the total DAP of a procedure, instead of the individual DAP values of each projection, could be used for the accurate estimation of the conceptus dose. Conceptus doses calculated using dose data normalized to ESD are about 23% higher compared to those estimated using data normalized to DAP. This discrepancy may be attributed to the contribution of scattering radiation from PA projection to ESD measurement of LC projection and vice versa. Therefore, dose data normalized to ESD do not provide accurate conceptus dose estimation. Doses normalized to DAP showed a dependence on (a) tube potential and (b) tube filtration. Data are provided to extent the doses normalized to DAP for the standard spectrum to other tube voltages and filtrations. The maximum dose for a potential conceptus was 0.425 mGy for a patient irradiated for 50 seconds during the PA projection and for 40 seconds during the LC projection. Although the total duration of fluoroscopy is usually less than 2 minutes during a typical procedure, screening time as long as 14 minutes has been reported in the literature for treatment of complex fractures. The relationship between conceptus dose and fluoroscopy time found in the current study showed that, in these cases, the radiation dose received by a conceptus may exceed 1 mGy. In conclusion, an accurate estimation of conceptus doses associated with fluoroscopically assisted surgical treatment of hip fractures can be made using the DAP normalized dose data provided in this study. Conceptus doses from a typical procedure is less than 1 mGy during all trimesters.

Radiation dose considerations in common paediatric X-ray examinations.

For paediatric radiology, diagnostic reference levels (DRLs) have been proposed by the National Radiological Protection Board and the European Commission, representing a baseline above which re-evaluation of the equipment and the techniques used is necessary. To measure the entrance surface dose (ESD) in various paediatric radiological examinations carried out at a large paediatric hospital in Greece and compare them with the existing DRLs. Measurements of ESD using thermoluminescent dosemeters were carried out in a sample of 168 paediatric patients who underwent various common radiological examinations (chest, skull, pelvis, lumbar spine, full spine). The patients were categorised according to age, and the mean ESD was calculated for each examination and age category. Additionally, the effective doses were estimated from measured ESD using appropriate conversion coefficients found in the literature. The mean ESD values were found to be well below the proposed DRLs for all the examinations studied except for the chest, owing to the low tube potential used and tube filtration. Even in examinations that did not exceed the DRL, patient protection can be optimised further by appropriate collimation of field size to that necessary for diagnosis.

Differences in effective dose estimation from dose-area product and entrance surface dose measurements in intravenous urography.

In this study, measurements of dose-area product (DAP) and entrance surface dose (ESD) were carried out in a sample of 25 adult patients who underwent intravenous urography (IVU). These measured quantities were used to estimate the effective dose E from the IVU examination, a quantity closely correlated to radiation risk. Estimating E involves the use of conversion coefficients that have been determined for specific X-ray views in a mathematical phantom. These are obtained under conditions which are not usually met in clinical practice. As a result, the E estimates using the two different measurable quantities can be quite different. Analysis of the calculation procedure suggests that the E estimate using the DAP measurements, in addition to being more practical, could be more accurate than using ESD measurements, as DAP is sensitive to the X-ray field size settings. Furthermore, it is shown that in the absence of the appropriate equipment, a reliable E estimate can be obtained from the ESD calculated using the exposure data for each X-ray view.

The potential for reduction of radiation doses to patients undergoing some common X ray examinations in Tanzania.

The potential for patient dose reduction in diagnostic radiology was investigated in five major Tanzanian hospitals. The aim of this study was to follow up previously reported suggestions for improved practices to achieve dose reductions. The suggestions were implemented and entrance surface dose measurement repeated by using well-calibrated LiF thermoluminescence dosemeters. The results show that dose reductions in chest PA X ray examinations ranged from 15% to 50%. For abdomen AP and pelvis AP X ray examinations, the dose reductions ranged from 24% to 73% and from 25% to 72%, respectively. The respective dose reductions for lumbar spine AP and LAT projections ranged from 4% to 58% and from 16% to 77%. Interestingly, the majority of radiographs obtained after the implementation of dose reduction measures were useful for intended diagnosis according to the opinion of radiologists. It is concluded that significant dose reductions can be achieved in the country without loss of diagnostic information. Such dose reductions also predict reductions of radiation risk to patients.

A Regional Dose and Image Quality Survey for Chest, Abdomen and Pelvis Radiographs in Paediatrics

A dosimetric survey in paediatric radiology is currently being carried out, aiming at the assessment of patient dose and image quality for chest, abdomen and pelvis radiographs in some age categories at five hospitals in the Tarragona area. Entrance surface dose measurements were performed using homogeneous PMMA phantoms. Effective doses were assessed through the application of published conversion factors. The range of entrance doses averaged by sites was 75-729 µGy for pelvis radiographs of children aged 5 months, 813-1600 µGy for pelvis radiographs of children aged 5 years, 94-250 µGy for chest radiographs of children aged 5 years and 980-2300 µGy for abdomen radiographs of children aged 5 years. The reference dose values given in the European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Paediatrics were exceeded at two or more hospitals for all projections. The range of average effective dose for the analysed examinations was 14-245 µSv. The maximum ratios of effective dose by sites varied between 2.2 and 11 for the analysed projections. By examination type, average values in the range 100 to 245 µSv were estimated for 5 year pelvis and abdomen examinations.

Reference dose levels for patients undergoing common diagnostic X-ray examinations in Irish hospitals.

Wide variations in patient dose for the same type of X-ray examination have been evident from various international dose surveys. Reference dose levels provide a framework to reduce this variability and aid in the optimization of radiation protection. The aim of this study was to establish, for the first time, a baseline for national reference dose levels in Ireland for four of the most common X-ray examinations: chest, abdomen, pelvis and lumbar spine. Measurements of entrance surface dose using thermoluminescent dosemeters (TLDs) for these four X-ray examinations were performed on 10 patients in each of 16 randomly selected hospitals. This represented 42% of Irish hospitals applicable to this study. Results have shown wide variation of mean hospital doses, from a factor of 3 for an anteroposterior lumbar spine to a factor of 23 for the chest X-ray. The difference between maximum and minimum individual patient dose values varied up to a factor of 75. Reasons for these dose variations were complex but, in general, low tube potential, high mAs and low filtration were associated with high-dose hospitals. This study also demonstrated lower reference dose levels of up to 40% when compared with those established by the UK and the Commission of the European Communities for four out of six projections. Only the chest X-ray exhibited a similar reference level to those established elsewhere. This emphasizes the importance of each country establishing its own reference dose levels that are appropriate to their own radiographic techniques and practices in order to optimize patient protection.

Evaluation of a MOSFET radiation sensor for the measurement of entrance surface dose in diagnostic radiology.

A patient dosimetry system using MOSFET technology (Thomson and Neilson Electronics Ltd, Canada) is evaluated for entrance surface dose measurements in diagnostic radiology. The system sensitivity for the standard MOSFET detector coupled to a high sensitivity bias supply was measured to be 1 mV mGy-1. Response of a new high sensitivity dosemeter was measured to be 3 mV mGy-1. The minimum detectable entrance surface dose at which a single measurement can be made with less than 25% total uncertainty at the 95% confidence level was estimated to be 4 mGy for the standard dosemeter and 1.5 mGy for the new high sensitivity dosemeter. The dosemeters were found to be linear with absorbed dose in air, linear with dose rate and reproducible, although they showed some energy dependence across the diagnostic energy range. The system is also compared with thermoluminescent dosimetry (TLD) as a tool for the measurement of entrance surface dose in diagnostic radiology. MOSFET detectors are considered to have advantages over TLD dosemeters with the instant readout of entrance surface dose. These dosemeters do have the disadvantage that they are visible in radiographs, they have a finite shelf life and can only accumulate absorbed dose up to a limiting value after which the dosemeters can no longer be used.

Typical Radiation Doses to Patients from Some Common X Ray Examinations in Tanzania

The results of entrance surface dose measurements on adult patients in diagnostic radiology are presented. The measurements were carried out using calibrated LiF thermoluminescence dosemeters for five simple projections of X ray examinations in major Tanzanian hospitals. The mean entrance dose per X ray examination at each hospital ranged from 0.1 to 0.9 mGy for chest AP, 3.5-13.9 mGy for abdomen AP, 1.6-13.1 mGy for pelvis AP, 3.6-12.7 mGy for lumbar spine AP and 10.0-29.6 mGy for lumbar spine LAT. Inter-hospital and intra-hospital dose variations up to a factor of 5 were observed for the same type of X ray examination, which suggests that operational conditions are not fully optimised. Under the limitations of the available resources, the techniques and skills employed are found to be the first possible sources of unoptimised doses to patients.

腹部IVRの際の患者の皮膚線量のリアルタイム測定

腹部IVRの際の患者の皮膚線量のリアルタイム測定

Clinical use of carbon-loaded thermoluminescent dosimeters for skin dose determination

Carbon-loaded thermoluminescent dosimeters (TLDs) are designed for surface/skin dose measurements. Following 4 years in clinical use at the Mater Hospital, the accuracy and clinical usefulness of the carbon-loaded TLDs was assessed. Teflon-based carbon-loaded lithium fluoride (LiF) disks with a diameter of 13 mm were used in the present study. The TLDs were compared with ion chamber readings and TLD extrapolation to determine the effective depth of the TLD measurement. In vivo measurements were made on patients receiving open-field treatments to the chest, abdomen, and groin. Skin entry dose or entry and exit dose were assessed in comparison with doses estimated from phantom measurements. The effective depth of measurement in a 6 MV therapeutic x-ray beam was found to be about 0.10 mm using TLD extrapolation as a comparison. Entrance surface dose measurements made on a solid water phantom agreed well with ion chamber and TLD extrapolation measurements, and black TLDs provide a more accurate exit dose than the other methods. Under clinical conditions, the black TLDs have an accuracy of +/- 5% (+/- 2 SD). The dose predicted from black TLD readings correlate with observed skin reactions as assessed with reflectance spectroscopy. In vivo dosimetry with carbon-loaded TLDs proved to be a useful tool in assessing the dose delivered to the basal cell layer in the skin of patients undergoing radiotherapy.