Objective
- EVALUATION OF RADIATION RISKS FROM ALL RADIATION SOURCES AND OPTIMIZATION OF RADIOPROTECTION.
- DEVELOPMENT AND COMPARISON OF NEW METHODS FOR OPTIMIZATION OF RADIOPROTECTION .
Numerous epidemiological studies on different populations exposed to ionising radiation were reviewed to derive exposure time risk surfaces for radiation induced cancer risks at low doses and dose rates.
Quantitative statistical methods were tested for their operation characteristics in the presence of confounding variables by means of the simulation codes SIRIS. The Monte-Carlo code generates synthetic epidemiological data whichthen were evaluated using the Cox proportional hazards model and the contingency table analysis based on Mantel-Haenszel techniques.
The data of the follow up study with patients exposed to radium-224 for therapeutic purposes were quantitatively evaluated by means of nonparametric methods and model fits to derive risk estimates for bone sarcomas and lens opacifications.
Various mathematical models that predict exposure time risk surfaces based on biological assumptions for radiation induced tumours were critically reviewed.
The derivation of risk estimates on the basis of epidemiological observation requires various extrapolations:
from medium/high doses (and dose rates) to low doses;
from limited observation periods to lifetime;
from the observed population to the population of interest for the risk assessment.
The functional dependencies needed for these extrapolations can not definitively derived from epidemiological studies. This stresses the importance of the need to clarify the physical and biological mechanisms underlying the induction of cancer by ionising radiation. In this context the modelling of primary physical interactions and effects seems to be a promising way in this direction.
Organ doses were calculated in certain homes and in open air for various relevant gamma emitters in the soil and on walls using Monte-Carlo methods. The accuracy and reliability of simplified calculation methods were checked and computed results were compared with experimental data.
Organ specific exposure rates were calculated for the internal exposure due to consumption of contaminated foodstuffs by members of the public and an assessment was made of the reliability and variability of these dose factors.
Results obtained in this study allow the assessment of external exposures in urban environments for various contamination scenarios. Besides different deposition patterns the effectiveness of decontamination measures can be studied. A model for the external exposure of the public after a deposition of radionuclides has been derived from these results. Due to several reasons the exposure over an open lawn has turned out to be a favorable location for the assessment of the external exposure in unshielded locations: most is known about the deposition on lawns, in case of accidents measurements on the deposition on lawns are performed routinely and the ratio of the exposure at other locations to the exposure over a lawn (location factor) was found to be constant in time or to gradually decrease smoothly. Therefore a realistic, but gradually overestimating method for the external exposure with increasing time after the deposition is obtained by multiplying the exposure over a lawn with location factors for the time of deposition.
Simple calculation methods for the buildup factor have not been proven to be generally applicable to the calculation of external exposure in urban environments. It has become evident that it is not worthwhile to develop calculation schemes which improve such a method. It is more favorable to use more exact methods like the Monte-Carlo simulation, since the computers have become much faster in the past 5 years and complex problems can no w be solved by these methods. Although great progress has been achieved in the past 5 years in the knowledge and modelling of the external exposure, there are several areas of uncertainty yet to be clarified. First, deposition and weathering of radionuclides on trees in urban environments, in light shafts for basements and indoors have to be known with a much greater accuracy than it is the case today. These deposition areas can considerably influence the external exposure outside, in basements and in living rooms in large buildings. Secondly, the external exposure from indoor photon sources has not yet been calculated in a satisfactory manner. Third, the dependence of the external exposure in basements on various parameters and the effect of decontamination measures on the external exposure could be better understood. The methods developed up until now could be used for the support of the management of emergency situations.
The need of anthropomorphic phantoms for the simulation of radiation transport in the human body raises the question how representative are the currently used mathematical phantoms in comparison to real persons. The development of so called voxed phantoms on the basis of computerised tomography (CT) or nuclrar magnetic resonance (NMR) tomography for external exposures promises a possibility to answer this question also for internal emitters. For the extrapolation of biokinetic data derived from adults suffers especially from a lack of knowledge of age dependencies. The only way to overcome this difficulty is the inforced development and use of physiologically based models for the relevant elements.
Another shortcome to the present situation is that the available models were developed exclusively for dose factor calculations but are in general not well suited for the assessment of actual incorporation events on the basis of measured body burdens. Here, models for short term retention, especially in the lungs, and excretion rates are urgentl y needed for incorporation surveillance.
The results of an evaluation of the available literature indicated that the quality of the database for the derivation of dose conversion factors varies largely among the various nuclides. The extrapolation of data derived from animal studies is highly questionable in many cases. This situation may be improved by use of stable isotopes in connection with studies with humans.
The research activities covered aspects of modelling of exposure situations for external radiation. Physical and mathematical exposure models were successfully used to generate necessary links between measurement and interpretation of doses.
Achieved progress can mainly be related to better modelling of the radiation source and the human body; further improvements were made concerning calculations of the radiation transport and the investigations on the influence of the quality factor definition.
Modelling of the radiation sources:
Radiation source modelling was extended to the occupational situation of irradiation from plane sources, (eg, contaminations of the ground following accidents). A ground source code was developed, starting with a simple one and later the presently used more detailed and sophisticated code. The simple version assumed a uniform distribution of radioactive material on the surface of a plane ground and neglected any absorption of the radiation in the air. The improved code allows not only for consideration of air absorption but also for absorption in the soil, if the active material is not on the surface but in the depth. The radioactive material can either be located as a thin homogeneous layer in a certain effective depth accounting for the surface roughness or it can be distributed uniformly throughout the soil as this is the case for the natural radionuclides.
Models of the human body:
Most of the heterogeneous mathematical phantoms in use for dose calculations are based on the International Commission on Radiological Protection (ICRP) Reference Man data. In 1982, 2 sex specific adult phantoms ADAM and EVA were introduced based on the design characteristics of the MIRD-5 phantom. According to the definition of the effective dose equivalent for the specification of numerical values of the effective dose equivalent (HE), sex specific phantoms are needed.
Although the body characteristics of the MIRD-type phantoms are in good agr eement with those of the reference man and woman, they have some disadvantages related to the location and shape of organs and the form of the whole body. Furthermore, the phantoms ADAM and EVA represent adults, which limits their applicability in calculation of radiation exposures of the members of the public. In order to overcome these disadvantages and to obtain more realistic phantoms, a technique based on computer tomographic (CT) data was developed. Thistechnique allows any physical phantom or real body to be converted into computer files which can be coupled to a code for organ dose calculations. Each organ and tissue of this voxel phantom consists of volume elements, derived from CT data. Therefore, the location and shape of the organs and tissues are accurately modelled. The following media are taken into account: hard bone, bone marrow, soft tissue, mucsle tissue, lung tissue, skin and air. Special care is given to the modelling of the red bone marrow. The relative amount of bone marrow in each voxel within the skeleton can be estimated from the bone marrow from the CT numbers of the respective bone pixels. Hence, the spatial distribution of the red bone marrow can be assessed with high resolution.
So far 3 voxel models have been constructed: 1 of an 8 week old baby, 1 of a 7 year old child and 1 of the Alderson Rando phantom which is a physical phantom used for dose measurements mainly in radiotherapy. The latter mathematical phantom was constructed in order to perform comparisons between measurements and calculations, and to compare calculations using the male MIRD-type phantom ADAM and the voxel model of an Alderson-Rando phantom. Organ dose conversion factors for these different types of phantoms are calculated.
Models of the radiation transport in matter:
The basis of the Monte-Carlo (MC) method for photon transport is the computer simulation of individual photon histories and the averaging of these histories over many thousands of photons to pro vide the quantities of interest. At each stage in a photon history, random numbers are used to select the parameters of the photon according to known probability distrubtions. The energy transferred in each photon interaction is assigned to a certain organ or tissue and summed up for the respective tissues. The doses are finally obtained by dividing the total energy deposited in a tissue by the mass of this tissue. The first MC codes assumed secondary particle equilibrium and, consequently, all energy transferred in a photon interaction was deposited at the point of interaction without taking into account any energy transfer to secondary electrons (kerma approximation). Most of the codes used now are able to transfer the photon interaction energy to secondary electrons which are further pursued.
After large environmental contaminations, the introduction of various activity limits for agricultural products used for human nutrition were considered in countries of the European community (EC) were analysed. The applicability and efficacies of various strategies were analysed for the usage of agricultural products with contamination levels above these limits as animal feed in such a way that the final contamination of the respective animal end product (eg milk, meat, eggs) are below those limits for human nutrition. The nuclides strontium-90, iodine-131, plutonium-239, americium-241, and caesium-137 were considered, and various feeding procedures could be identified in which agricultural products with contamination levels more than 10 times the limits for human consumption could safely be used as feed.
This experience has clearly shown, that it remains doubtful whether single criteria or multicriteria decision making in the optimisation of radiation protection measures will lead to a higher acceptability of the minimised total detriment strategy. However, the assumptions and priorities underlying a decision process will become more transparent. It is important to assess also the actual feasability of an optimum strategy. In the context of contaminated agricultural products, it must be expected that in a given situation the public market and political considerations might lead to different priorities thus to the realisation of different decisions.
Numerous papers and books published in the open literature on cost benefit analyses in the public domain where evaluated. However, interviews with decision makers in administrations and in industry has clearly shown that actual decisions are mainly influenced by subjectively perceived opinions, which can not be quantified for mathematical procedures in decision theory.
Cost benefit analyses are actually used in industry only to compare the expected utilities from various alternatives. These utilities for a comp any can sometimes be expressed in monetary values in most cases. The net effects on the environment and on public health, however, can not be reduced easily to financial units. Thus, multicriteria decision methods must be used by those responsible for permitting the realisation of an alternative chosen as optimum by a company. The actual importance for the whole system of those parameters which can not be expressed in monetary values make quantitative and comprehensive optimisation studies rather difficult and open to discussion. However, they essentially contribute to the transparency of a decision process and the subjective preferences expressed.
A prerequisite for optimisation strategies is the knowledge of comparable risks (or of risks attributable to alternative decisions). Therefore a great number of common risks were quantified. Also a number of technological risks were included to allow comparisons with risks of new technologies. In this way they can be put into perspective with those already accepted.
Risks attributed to the construction of energy systems have been assessed thoroughly for nuclear power, hard coal and hydropower plants. The total investment figures were broken down into branches of the construction activities and the corresponding manpower was then calculated using productivity numbers. The German workmen's compensation insurance statistics were used to evaluate the anticipated construction risks. Construction risks have been calculated for a model power plant. The risk figures obtained demonstrate that construction risks of power plants form a substantial share of the total risks from all steps of fuel cycles.
A worldwide standardisation of methods and systems would be very desirable.
In the past few years the concept of the quality factor Q in radiation protection has been widely discussed. Various proposals for Q as a function of linear energy transfer (LET) or lineal energy (y) have been made in order to consider results of radiobiological experiments indicating a higher radiobiological effectiveness (RBE) of neutrons than expressed by the quality factor for neutrons according to the present convention.
The consequences of the different proposals were, by Monte-carlo calculations, analysed for photons for the effective dose equivalent (HE) in the anthropomorphic phantoms ADAM and EVA, and the ambient dose equivalent H*(10) in the ICRU sphere (10, 30). Accordingly, each of the proposals leads to different functions of the effective quality factors for HE and H*(10); none of them yielded an energy range with Q to be energy independent and equal to unity. A reasonable compromise was developed here, as part of the projects's results, by proposing a definition.
From this, the maximum deviation in Q for photons from unity would be about 10%, while Q for neutrons follows, (eg, the ICRU 40 recommendations).
The ICRP has recommended a system of dose limitation based on the effective dose equivalent HE. As HE is a complex quantity and not measurable, ICRU recommended an estimation of HE from the ambient dose equivalent H*(10). To ensure H*(10) to be a conservative estimate for HE, H*(10) and HE were compared on the basis of Monte-Carlo calculations. It could be shown that H*(10) exceeds HE in case of the anthropomorphic phantoms ADAM and EVA and external photon radiation under all exposure conditions considered. After the Chernobyl reactor accident intensive assessments of doses to members of the public were performed. With the new realistic voxel phantoms based on whole body computer tomographic (CT) data, effective dose equivalents for children were calculated. The results show that a dosimeter calibrated in terms of H*(10) is suitable for es timating HE to the public in the entire photon energy range of interest.
Statistical evaluation of the annual data from the Gesellschaft fuer strahlen und Umweltforschung (GSF) Personnel Dosimetry Service revealed trends of the total collective dose, the number of persons being monitored and the number of persons with an individual dose exceeding 0.1 mSv at least in 1 month of the calendar year. The analysis was made for the main protection areas (ie medicine, nuclear technology, conventional industry, research establishments etc).
The results show that the mean annual doses for large groups are below 0.1 of the limits, even for the most exposed subgroups, but that there are individuals, especially those involved in maintenance of nuclear power plants and in certain fields of medicine, with annual dose equivalents of 20 mSv and above for many years. These people, although observing the annual dose limit in every year of their occupational life, are at a risk much greater than that implicitly attributed to the chosen value of the annual dose limit.
A compilation of the dosimetric data obtained since 1980 shows, that the collective dose resulting from medical applications remained almost constant at around 8 manSv. The collective dose resulting from industrial applications, however, varies remarkably in the course of the years. Nevertheless, an overall reduction of the total collective dose is obvious. The mean annual doses of all persons monitored seem to confirm this development, but the decrease is mainly due to the steady increase in number of persons monitored. Considering only the exposed persons, the situation looks different; accordingly, the mean annual dose of these persons first increased during 1980 to 1982, decreased afterwards and finally remained constant since 1984.
In order to assess individual dose histories and lifetime doses, the personal dose records of a subgroup of 18,300 occupationally exposed persons was analysed, who were continuously monitored in the years 1980 through to 1986. 191 of them received an an nual dose equivalent higher than 10 mSv (medicine 26 individuals, research 2, industry and nuclear power production 163). A limitation of the lifetime dose eqivalent to 400 mSv, as discussed in the Federal Republic of Germany, would hence affect only few radiation workers.
X-ray diagnosis:
In order to determine workplace specific dose values for occupational exposed persons, measurements were performed at selected workplaces in diagnostic radiology, including digital substraction angiography (DSA), cardiac catheterisation and conventional angiographic examinations. To this end physicians and assistants were provided with 7 types of partial body dosimeters to be worn in addition to the usual personal dosimeter. This set of dosimeters, part of them specially designed for this study, comprised 2 thermoluminescent dosimetry (TLD) finger rings for the right and left hand, 2 TLD wristlets for the arms, a plastic button containing a TLD chip to be fixed by adhesive tape near the eye, and 2 small plastic boxes, both filled with 4 thermoluminescent (TL) dosimeters, to be worn below and outside of the lead apron next to the usual personal dosimeter.
The results show that the personal dosimeters covered by the lead apron nearly always indicates monthly dose values below 0.1 mSv whereas the dosimeters outside, worn at the collar of the apron, are remarkably higher, ranging in general between 0.3 mSv and 3 mSv with extreme values up to 12 mSv. A significant correlation between personal dose (below apron), dose at the collar and dose at the eyes could not be detected. Special emphasis was given to the analysis of doses to the finger rings and the wristlets. Finger rings are disturbing, they reduce the finger sensation, complicate sterility and the handling causes inconveniences. There is a pronounced reluctance on the side of physicians to wear such devices. In order to avoid finger rings for partial body dosimetry an alternative may be to substititute them by less disturbing wristlet dosimeters if a reliable, constant relation between dose to the finger and dose to the wrist exists.
Beta radiation in power plants:
The objective of this study was to identify relevant beta fields and to evaluate qualitative and quantitative figures on source and field parameters. The figures have been considered to be the basis for requirements for a personal dosimeter capable to detect beta radiation and allow for correct dose assessment in mixed photon beta fields. Measurements were made at a boiling water reactor (BWR) during both the operational and maintenance phase using survey meters with ion chamber technique, Geiger-Mueller (GM) counter, film and TL dosimetry. Preliminary results revealed dose rates up to around 0.2 Sv/h, resulting from extended contaminations and beta energies of around 0.5 MeV. Similar experiments were started in fuel element production applying different integrating dosimeter types for comparison.
Partial body dosimeter:
The development of a partial body thermoluminescent (TL) dosimeter together with the prototype of a personal computer (PC) assisted TL readout device was completed. The extremity type dosimeter is based on a plastic ring with a single beryllium oxide chip on a stainless steel support also used as a heating planchet. Each ring carries an identification code. The TL sample is hermetically sealed with a special foil for mechanical and optical protection equally resistant against the annealing procedure, chemical solvents and gas sterilisation.
The readout device provides automation for magazine transport (20 dosimeters), readout cycle, code reading and documentation. The TL signal is transmitted to the tube by a flexible fluid light pipe to reduce thermal effects. The PC assisted dose assessment is based on photon counting and a digital signal treatment.
On the basis of about 3500 test runs with more than 600 beryllium oxide detectors it was shown that, in partial body dosimetry, all specifications of a relevant standard could be fulfilled. Further activities were addressed to the reduction of optical fading and system application in beta ray dosimetry, particularly H'(0.07) assessment.
Film dosimeter badge:
The development and design of a new film dosimeter badge was completed, the absorption filter set optimised for the filteranalytical linear combination method for dose evaluation of the detector films. The badge contains 4 filters (copper 0.05 0.3 and 1.2 mm in thickness, lead 0.8 mm). There is an indicator for the radiation incidence direction made from densimet material. The badge design considers the automatic processing of the detector films. Integration of a (TL) assembly into the badge is continuing to provide a dual system (TL for dosimetry, film for exposition analysis).
Albedo dosimeter:
A TL neutron albedo dosimeter was prepared for radiation workers in nuclear industry, based on a commercial TL system with 2 pairs of lithium borate detectors enriched and depleted in the lithium-6 and boron-10 content and encapsulated in a boron cassette. Primary calibration refers to a americium beryllium neutron source. In order to correct for the spectral response, onsite field calibration was performed at nuclear facilities using a 30 cm polyethylene sphere. Conversion coefficients were evaluated for different spectral conditions to convert apparent doses, in terms of caesium-137 gamma rays, into dose equivalents.
The quantification of somatic radiation risks of low doses of ionizing radiation remains an important problem of scientific and practical interest. This is parcticularly true after the publication of the new results from the Radiation Effects Research Foundation (RERF) in Japan, indicating significantly higher somatic radiation risks than hitherto assumed.
The original, individual data of the RERF Life Span Study (LSS) data base files were adapted to a parallel computing environment. This input data set is now available on the INTEL HYPERCUBE computer to be used for modification by SIRIS.
The simulation program SIRIS has been extended to be able to take into account differential base line risk values changing with calender year. SIRIS can now calculate stochastic epidemiological data sets for further analysis. The output routines have been adapted to the requirements of AMFIT.
The statistical analysis program AMFIT has been transferred to the HYPERCUBE under UNIX. It is now ready for the production runs. Test runs have already been carried out to check the consistency of various models with the original data set.
For graphical analysis of the multidimensional output data the program set PV-WAVE has been implemented on the SUN workstation used as front end computer.
Quantification of radiation risks, optimization procedures and analysis of occupational exposure
The quantification of somatic radiation risks (ie the probabilities for the induction of cancer or leukaemia by radiation) of low doses of ionizing radiation remains an important problem of scientific and practical interest. This is particularly true after the publication of the new results from the Radiation Effects Research Foundation in Japan indicating significantly higher somatic radiation risks than hitherto assumed. The quantification problems are mainly due to various uncertainties regarding the extrapolation of radioepidemiological data presently available to:
future times (until all members of the collective have died);
lower doses than 1 Gy;
lower dose rates than acute irradiation;
other populations than those from which risk factors were derived;
other types of radiation fields (eg neutrons and alpha particles).
In this project the data of the most important radioepidemiological study (ie the Japanese Life Span Study of the atomic bomb survivors of Hiroshima and Nagasaki) will be used in close cooperation with the Departments of Epidemiology and Statistics of RERF to establish estimates of the confidence limits for the somatic risk factors:
at low doses and low dose rates (by analysis of the shape of the dose-response curves);
at future times (by employing different time extrapolation models);
for the contribution from neutrons (by comparing the responses in both cities).
This will be done by application of the stochastic simulation program for epidemiological data SIRIS, which has been developed by the GSF recently in the framework of the present CEC Research Programme, in combination with the advanced statistical evaluation program AMFIT developed recently by Preston and Pierce at RERF, and which is employed in the RERF-Analysis work and in the preparation of the BEIR-V Report of the US Academy of Science.
The original individual data of the Life Span Study Database (differential in age at exposure, sex, city, organ doses due to photons and neutrons, and the local base line risk of mortality) will be used, together with various dose-time response models, to calculate with the Monte Carlo simulation-program SIRIS sets of late effects for the same population with the same radiation exposure. These artificial epidemiological data will be used to evaluate with AMFIT the statistically significant conclusions based on the original data, and to attempt to estimate the regions of various somatic risk factors and their sensitivity to underlying model assumptions. To technically achieve this goal:
the voluminous RERF-data have to be brought into appropriate form;
the AMFIT-program has to be transported onto the computer on which the SIRIS-program is executed to allow a direct analysis after each (of thousands) of the simulations.
Further on, several plausible parameter sets of dose-time-effect models for late effects (relative, absolute, linear-quadratic models, etc.) have to be developed in close cooperation with the partners of RERF.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences chemical sciences inorganic chemistry alkaline earth metals
- natural sciences physical sciences nuclear physics
- natural sciences chemical sciences nuclear chemistry radiation chemistry
- natural sciences physical sciences theoretical physics particle physics photons
- natural sciences mathematics applied mathematics mathematical model
You need to log in or register to use this function
Programme(s)
Multi-annual funding programmes that define the EU’s priorities for research and innovation.
Multi-annual funding programmes that define the EU’s priorities for research and innovation.
Topic(s)
Calls for proposals are divided into topics. A topic defines a specific subject or area for which applicants can submit proposals. The description of a topic comprises its specific scope and the expected impact of the funded project.
Data not available
Calls for proposals are divided into topics. A topic defines a specific subject or area for which applicants can submit proposals. The description of a topic comprises its specific scope and the expected impact of the funded project.
Call for proposal
Procedure for inviting applicants to submit project proposals, with the aim of receiving EU funding.
Data not available
Procedure for inviting applicants to submit project proposals, with the aim of receiving EU funding.
Funding Scheme
Funding scheme (or “Type of Action”) inside a programme with common features. It specifies: the scope of what is funded; the reimbursement rate; specific evaluation criteria to qualify for funding; and the use of simplified forms of costs like lump sums.
Funding scheme (or “Type of Action”) inside a programme with common features. It specifies: the scope of what is funded; the reimbursement rate; specific evaluation criteria to qualify for funding; and the use of simplified forms of costs like lump sums.
Coordinator
85764 NEUHERBERG
Germany
The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.