mSv Effective Dose Research Articles

Hybrid computational phantoms representing the reference adult male and adult female: construction and applications for retrospective dosimetry.

Currently, two classes of computational phantoms have been developed for dosimetry calculation: (1) stylized (or mathematical) and (2) voxel (or tomographic) phantoms describing human anatomy through mathematical surface equations and 3D voxel matrices, respectively. Mathematical surface equations in stylized phantoms are flexible, but the resulting anatomy is not as realistic. Voxel phantoms display far better anatomical realism, but they are limited in terms of their ability to alter organ shape, position, and depth, as well as body posture. A new class of computational phantoms called hybrid phantoms takes advantage of the best features of stylized and voxel phantoms-flexibility and anatomical realism, respectively. In the current study, hybrid computational phantoms representing the adult male and female reference anatomy and anthropometry are presented. These phantoms serve as the starting framework for creating patient or worker sculpted whole-body phantoms for retrospective dose reconstruction. Contours of major organs and tissues were converted or segmented from computed tomography images of a 36-y-old Korean volunteer and a 25-y-old U.S. female patient, respectively, with supplemental high-resolution CT images of the cranium. Polygon mesh models for the major organs and tissues were reconstructed and imported into Rhinoceros™ for non-uniform rational B-spline (NURBS) surface modeling. The resulting NURBS/polygon mesh models representing body contour and internal anatomy were matched to anthropometric data and reference organ mass data provided by Centers for Disease Control and Prevention and International Commission on Radiation Protection, respectively. Finally, two hybrid adult male and female phantoms were completed where a total of eight anthropometric data categories were matched to standard values within 4% and organ volumes matched to ICRP data within 1% with the exception of total skin. The hybrid phantoms were voxelized from the NURBS phantoms at resolutions of 0.158 × 0.158 × 0.158 cm and 0.126 × 0.126 × 0.126 cm for the male and female, respectively. To highlight the flexibility of the hybrid phantoms, graphical displays are given of (1) underweight and overweight adult male phantoms, (2) a sitting position for the adult female phantom, and (3) extraction and higher-resolution voxelization of the small intestine for localized dosimetry of mucosal and stem cell layers. These phantoms are used to model radioactively contaminated individuals and to then assess time-dependent detector count rate thresholds corresponding to 50, 250, and 500 mSv effective dose, as might be needed during in-field radiological triage by first responders or first receivers.

Radiation dose for thoracic and coronary step-and-shoot CT using a 128-slice dual-source machine in infants and small children with congenital heart disease

For coronary artery visualization, retrospective ECG-gated acquisition by dual-source computed tomography (DSCT) was superior to spiral non-ECG-gated acquisition in a paediatric population of congenital heart disease (CHD) patients. However, retrospective cardiac CT is associated with substantial radiation doses to the patient. Recently, DSCT with end-systolic reconstruction was found to be robust for imaging the coronary arteries in patients with high heart rates. To evaluate step-and-shoot DSCT with end-systolic reconstruction for evaluating the heart, coronary arteries and other thoracic structures in young children with CHD. All neonates and children younger than 6years of age who were referred to our institution for CHD evaluation between September and October 2009 were included in the study. ECG-gated DSCT was performed in sequential prospective mode centred on the systolic phase identified by ECG analysis. To assess the radiation dose, we recorded the dose-length product (DLP) in mGy·cm and the effective dose in mSv estimated from the DLP. Overall image quality was evaluated using a 5-grade scoring system and was assessed by looking at cardiac and vascular structures. The image quality for the proximal and middle segments of the right and left coronary arteries was also evaluated using a 5-grade scale. Images of diagnostic quality (grade ≥ 3) were obtained in all 30 children with a mean image quality grade of 4.7 ± 0.6 (range, 3-5). Mean DLP was 5.7 ± 4.8mGy*cm (range, 1-22mGycm) and mean effective radiation dose was 0.26 ± 0.16mSv (range, 0.05-0.8mSv). Prospective ECG-gated thoracic DSCT at end-systole usually provides adequate thoracic and coronary artery image quality in neonates, infants and young children with CHD, independent of heart rate. This new method is associated with lower radiation doses compared to previous literature (mean effective dose, 0.26mSv).

Radiation protection in newer imaging technologies

Not even a week passes without a paper getting published in peer reviewed journals on radiation protection in newer imaging technologies that either did not exist 10 y ago or were not established for routine use. Computed tomography (CT) happens to be a common element in most of these technologies. Radiation protection is high on the agenda of manufacturers and researchers and that is becoming a driving force for users and international organisations. The media and thus the public have their own share in increasing the momentum. The slice war seems to be shifting to dose war. Manufacturers are now chasing the target of sub-mSv CT. The era of two digit mSv effective dose for a CT procedure is far from losing ground, although cardiac CT within 5 mSv seems possible. A few years ago the change in technology was faster than adoption of dose management but currently even the development of dose reduction techniques is faster than its adoption. There is dearth of large-scale surveys of practice and lack of surveys with change in technology.

Clinical Summaries

Clinical Summaries

Human radiation dosimetry of [11C]MeAIB, a new tracer for imaging of system A amino acid transport

[N-methyl-11C]alpha-methylaminoisobutyric acid ([11C]MeAIB) is a promising positron emission tomography (PET) tracer for imaging hormonally regulated system A amino acid transport. Uptake of [11C]MeAIB is totally specific for amino acid transport since [11C]MeAIB is metabolically stable both extra- and intracellularly. The aim of this study was to measure cumulated radioactivity in different organs and estimate the absorbed radiation doses to humans with the Medical Internal Radiation Dosimetry (MIRD) method. Radiation absorbed doses were calculated from PET images for 25 volunteers. Dynamic acquisition data were obtained for the thoracic, abdominal, femoral and head and neck regions. The median dose of intravenously injected [11C]MeAIB was 422+/-35 MBq, with a range of 295-493 MBq. After PET imaging the radioactivity in voided urine was measured. Experimental human data were used for residence time estimates. Radiation doses were calculated with commonly used software. The effective dose for a 70-kg adult was 0.004 mSv/MBq, corresponding to a 1.72 mSv effective dose from the PET study with injection of 430 MBq [11C]MeAIB. The highest absorbed doses were in the pancreas (0.018 mGy/MBq), kidneys (0.017 mGy/MBq), intestine (0.014 mGy/MBq), liver (0.008 mGy/MBq) and stomach (0.005 mGy/MBq). Only 0.57% of injected activity was excreted to urine within 1 h after injection. Biodistribution of [11C]MeAIB in the abdominal region reflected the high activity of the transportation of amino acids via system A and these organs also had the highest radiation doses. An effective dose of 0.004 mSv/MBq is fully justified when [11C]MeAIB PET is performed to study system A activity in vivo.

Assessment of effective dose from concomitant exposures required in verification of the target volume in radiotherapy.

The requirement of the Ionising Radiation (Medical Exposure) Regulation 2000 [IR(ME)R] of justifying all exposures to ionizing radiation includes those from radiotherapy double exposure portal images resulting in exposure to normal tissues outside the treatment volume. Typical effective doses were calculated for a range of common sites using CT data to outline those parts of specific organs subject to concomitant radiation and generate dose-volume histograms. The product of the mean dose and the relative probability of inducing a fatal cancer in specific organs was used to determine a representative total effective dose in mSv per monitor unit for each site. A table of representative effective doses, ranging from 0.32 mSv to 2.56 mSv per monitor unit, was produced, which may be used to monitor cumulative effective doses of individual patients from double exposure portal images, in addition to those received from localization procedures.

Use of group monitoring data in lung dose estimation for intakes of uranium

This paper describes an internal dosimetry program developed for Canadian uranium processing facilities. The recently adopted recommendations of ICRP Publication 60 have made it extremely difficult to detect intakes of insoluble forms of natural uranium by in vivo methods (lung counting). A type S intake of UO2 corresponding to a 20 mSv effective dose has a lung burden that is a factor of 2-3 lower than the MDA, 6 months after the intake occurred. A new methodology, approved in principle by the Canadian Nuclear Safety Commission, has been designed to overcome this problem by summing sequential, but separate, lung counts for an individual, or summing lung counts from a group of workers performing similar tasks. This summing technique effectively increases the counting time and, therefore, reduces the MDA to a value below the dose limit. Doses will be assigned to the individual or work group based on the average lung burden.

Erfassung und Bewertung der Patientenexposition in der diagnostischen Radiologie und Nuklearmedizin

The regular annual monitoring of patient exposure in radiation diagnostics, as performed by the Federal Office for Radiation Protection (BfS), plays an important role in evaluating the awareness of radiological quality and safety in Germany and the risk-benefit optimization for patients. For the reporting year 1997, X-ray diagnostics resulted in a mean effective dose of 2 ± 0.5 mSv per head of population. The underlying frequency of medical X-ray examinations was approximately 136 million, i. e., 1.7 examinations annually per head of population. In terms of nuclear medicine diagnostics, the patients exposure amounted to approximately 0.15 mSv effective dose per head of population. In this case, the number of examinations amounted to approximately 4 million, corresponding to a frequency of approximately 0.05 examinations annually per head of population. The paper discusses factors influencing the calculation of exposure, as well as the lack of an internationally accepted protocol to evaluate patient exposure.

Reconstruction of the inhalation dose in the 30-km zone after the Chernobyl accident.

Due to lack of measurements of activity concentrations in air, the assessment of the inhalation dose of the population evacuated from the 30-km zone after the Chernobyl accident is not possible from continuous filter measurements. Since the evaluation of the inhalation dose in each settlement of the zone is of great interest for epidemiological purposes, an approach was chosen that utilizes the available data on ground deposition of 137Cs, a recently performed best estimate of the radionuclide vector and its spatial distribution as well as the radionuclide dependent deposition velocity. The derived inhalation dose values in the 30-km zone range between 3 mSv to 150 mSv effective dose for adults depending on the distance to the reactor site and the day of evacuation. For 1-y-old infants the values range between 10 to 700 mSv. In Chernobyl town, an effective inhalation dose of 25 mSv until evacuation day was assessed. Thyroid doses due to inhalation ranged from 0.02 to 1 Sv for adults, for 1-y-old infants from 0.02 to 6 Sv. The inhalation dose in each settlement of the 30-km zone is approximately 8-13 times higher than the external exposure in each settlement if evacuation of the settlement occurred at an early stage. For settlements with evacuation at a later stage (day 10 or later) the inhalation dose was about 50-70% higher than the external dose. The dominant contribution to the effective inhalation dose comes from 131I (about 40%) and tellurium and rubidium isotopes (about 20-30%). Despite high zirconium and cerium ground depositions, zirconium and cerium isotopes contribute rather little to the inhalation dose which is mainly due to the great particle sizes to which they are attached. The relative contribution of short-lived radionuclides is, despite higher activities than at greater distances, less than 5%.

IRID: Ionising Radiations Incident Database(First Review of Cases Reported and Operation of the Database)

One of the main ways accidents can be prevented is to learn lessons from previous incidents or `near-misses'. So it was that the Ionising Radiations Incident Database (IRID) was set up in 1996 by HSE, EA and NRPB (the `partners'). In essence, each radiation incident is reduced to a set of data codes on a proforma and entered onto the database by NRPB who maintain it. The data codes are grouped within 23 fields and a further one enables a written description. Fields cover such matters as doses, occupation of workers, equipment involved, nuclides, causes and follow-up. Preservation of anonymity and confidentiality are important considerations, and incidents which are sub judice are excluded. So far, only the `partners' have supplied data, some back to the 1970s, and this report gives an assessment of the first 100 (convenient for percentage descriptions!). Importantly, the incidents predominantly cover the non-nuclear sector, and exclude nuclear, transport and patient exposure incidents which are covered by other arrangements. Exposures up to 370 mSv (average 15 mSv) effective dose and 60 Sv extremity dose are reported. The report gives statistical analyses of the incidents on the basis of a number of the fields, backing this up with several tables of data. Thus it can be seen that industrial radiography is the most common cause of incidents (one third of total), followed by level/density/moisture gauges (one fifth) and scrap material processing (one tenth). Exposures are predominantly external rather than from contamination. The analyses also lead to a number of lessons for users and are backed up by examples. There are lessons for us all here, and while none of them are new, they are well worth rehearsing: `ensure proper management systems are in place'; `use a monitor'; `maintain security and supervision of radioactive materials at all times'; `train your operators'; `be prepared for incidents' and `take care of personal dosemeters'. Undoubtedly though, the main value of the report is in the descriptions of 84 case studies which take up most of its volume. These have been categorised into seven areas (e.g. unsealed radioactive materials, density gauges, recycling and scrap metal), each incident taking up just one page. Together with some drawings, they are freely available to use and reproduce, making an invaluable aid to employers, trainers, RPAs etc. This is a well structured, useful report which acknowledges that the next stage is to expand the database and get contributions from those not yet involved (i.e. the non-`partners'). To this end, there is a returnable questionnaire, but it is a pity that the report was not made freely available. The �15 price tag may well mean a biased level of response.

Assessment of plutonium exposures in Rongelap and Utirik populations by fission track analysis of urine

A nuclear device, code-named Bravo, detonated at Bikini Atoll at 6:45 a.m. on 1 March 1954, unexpectedly released a large amount of radioactivity. Over 40 years after this incident, the study of its impact on the radiological health and environmental safety of the residents of Rongelap and Utirik Atolls continues. In 1987, researchers at Brookhaven National Laboratory established a fission track analysis (FTA)_method for low-level 239Pu urinalysis. Two years later, a new shipboard protocol was developed for collecting 34-h radiologically clean urine samples. The purpose of this paper is to update information on the FTA method for measuring low-levels of plutonium, and to summarize results on the distribution of 239Pu in the populations of Rongelap and Utirik between 1981–1991. Plutonium detection levels (99% confidence level) in these samples were 2–3 μBq, which is equivalent to 0.2–0.3 mSv effective dose equivalent (EDE) to age 70 for Marshallese. The latest 1991 FTA data indicate average EDE of 0.62 mSv and 1.6 mSv for the people of Rongelap and Utirik, respectively, which both are the highest values since 1988.

Low‐level radiation — How dangerous is it?

The main delayed effect of ionizing radiation in the individual is the induction of cancer. However, for low doses (less than 100 mSv effective dose equivalent), there is no direct evidence of radiation-induced cancer, with the possible exception of childhood cancer following prenatal exposure to X-rays. The risk at low doses has to be estimated from the observed risk at high doses; there are considerable uncertainties in this extrapolation. Direct study of those exposed to low doses does not produce any more precise information, although it does impose boundary conditions on the risk. Currently the most important problem in environmental radiation exposure is the increased incidence of childhood leukaemia observed around some nuclear installations; the explanation for this remains unclear.

Correlation among the terrestrial gamma radiation, the indoor air 222Rn, and the tap water 222Rn in Switzerland.

The external gamma radiation and the indoor air Rn (222Rn) concentration were measured in 55 houses of the South East Grisons, the Urseren valley, and the Upper Rhine valley (crystalline subsoils) and in 39 houses of the Molasse basin and the Helvetic nappes (sedimentary subsoils). In homes located on a crystalline subsoil, a mean cellar gamma level of 1.40 mGy y-1 was measured, which is twice the mean gamma level of 0.70 mGy y-1 found in homes built on a sedimentary subsoil. The cellar 222Rn gas concentration is about six times higher in houses with a crystalline subsoil (1232 Bq m-3) than in houses with a sedimentary subsoil (201 Bq m-3). Although a weak correlation is observed between the mean gamma radiation levels and mean cellar 222Rn gas concentrations for the five subregions investigated, the gamma levels and the 222Rn gas concentrations do not correlate for single homes. For the population living on the ground floor of a house with a crystalline subsoil, the gamma radiation and the indoor air 222Rn lead to estimated mean exposures of 1.16 mSv and 9.44 mSv effective dose equivalent per year, respectively. In houses with a sedimentary subsoil, these mean exposures lead to 0.68 mSv y-1 and 3.22 mSv y-1, respectively. A mean tap water 222Rn content of 38.3 Bq L-1 and 10.4 Bq L-1 was measured in 31 villages with a crystalline subsoil and 73 villages with a sedimentary subsoil, respectively. Radon-222 degasing from the tap water into the indoor air leads to an additional exposure of about 0.11 mSv y-1 and 0.03 mSv y-1 in homes with a crystalline subsoil and homes with a sedimentary subsoil, respectively.

Indoor Rn levels in different geological areas in Switzerland.

The distribution of indoor Rn concentrations in different geological areas in Switzerland was studied using passive alpha-track detectors. Measurements involving a sample of 400 single-family homes were made in the cellar, on the ground floor and the first floor, respectively. On the basis of a pilot survey, the country was divided into four zones in which the Rn distribution in houses was analyzed separately. The indoor exposure to Rn and Rn decay products is quite variable from region to region. The geology of the different areas was found to be an important factor in determining the mean value Rn levels. In the basin north of the Alps, where the population centers are located, a median Rn gas level of 47 Bq m-3 for the living area was found. The arithmetic mean value of 60 Bq m-3 in this region leads to an annual effective dose equivalent of about 1.8 mSv. For the population living in alpine areas, an arithmetic mean value exceeding 200 Bq m-3 will lead to an annual effective dose equivalent in the range of 6 mSv. The estimated exposure to Rn and Rn decay products for the upper one-percentile of the homes in the most affected alpine region even exceeds the annual limit of 50 mSv effective dose equivalent for occupational exposure.

Influence of Subsoil Geology and Construction Technique on Indoor Air 222Rn Levels in 80 Houses of the Central Swiss Alps

The indoor 222Rn level depends mainly on the subsoil geology, the cellar floor permeability, the cellar aeration, the air-tightness of the homes, and the aeration habits of the occupants. These five parameters and the 222Rn levels in the cellar and in the living room on the ground floor were compiled in 80 one- or two-family houses of the central Swiss Alps. The 222Rn levels were measured with passive alpha track detectors. Houses located on a granite, ortho-gneiss or verrucano subsoil have a cellar 222Rn level that is on the average 4.4 times higher than houses which are built on grey-schist or sediments. The cellar level is on the average 5.4 times higher if the cellar has partially a gravel or earth floor than if the whole cellar surface is covered with a concrete floor. Energy-efficient, highly air-tightened homes have a living room level that is on the average 1.8 times higher than normally insulated conventional homes. In the cellars and the living rooms of the 80 houses considered, arithmetic mean 222Rn levels of 724 Bq m-3 (20 pCi L-1) and 178 Bq m-3 (4.8 pCi L-1), respectively, were found. In the central Swiss Alps 222Rn and 222Rn decay products lead to an estimated mean exposure of 5.3 mSv effective dose equivalent per year.