Achievements were made in the following areas:
Dosimetric modelling - support for ICRP Committee 2 Task Groups.
Physiological parameters for respiratory tract modelling.
Deposition of inhaled radionuclides in the respiratory tract.
Clearance of radioactive material deposited in the respiratory tract.
Development of improved methods of assessing intakes of radionuclides.
The objectives of the contract have been fully met. The studies have advanced our knowledge on the potential of new chelators, notably 3,4,3LI(1,2-HOPO) for the decorporation of Pu, Am and Th. The work has also drawn attention to some of the limitations of those substances recommended currently and where alternative regimes may be at least as effective. The future use of 3,4,3LI(1,2-HOPO) in humans will depend on the results of comprehensive toxicity testing and an improved method of synthesis. Some progress has been made on the decorporation of uranium, neptunium and polonium, but more effective regimens are still required.
A detailed investigation has been undertaken at UB of the distribution of natural alpha radioactivity within the human fetus, using autopsy samples obtained from various stages of development from 18 weeks to stillborn.
Measurements have been made at NRPB of concentrations of (210)Po and other alpha-emitters in fetal tissues obtained from second trimester terminations carried out in the Oxford area and in west Cumbria.
CEA and NRPB have studied the transfer of polonium-210, plutonium-239 and other actinides to the fetus in late gestation in a primate species, the baboon. Results from two mothers and fetuses are complete, measurements having been made 7 days after intravenous injection at 5 months of gestation.
Autoradiographic studies using a beta emitter, (241)Pu have been undertaken to obtain information on the microdistribution of Pu in relation to sensitive cells in the yolk sac and other tissues.
Studies at CEA, designed to estimate doses delivered to fetal tissues and organs during development, have involved measurement of the skeletal distribution of different radionuclides with differing energies, and analysis of biological effects. The studies have been focussed on the uptake of radionuclides by the skull with the aim of studying effects on the brain.
MBL/ITRI-TNO have undertaken studies to facilitate the separation and characterisation of haemopoietic stem cells using a combination of cell separation techniques, reverse transcriptasepolymerase chain reaction and cell culture methods.
CIEMAT have investigated whether irradiation with doses as low as 0.5 Gy (X-rays) will induce persistent haemopoietic damage in particular stages of murine development.
With the aim of obtaining information relating to the molecular basis of persistent haemopoietic deficiencies observed after irradiation, analyses of the expression of haemopoietic growth factors (HGFs) have been undertaken at CIEMAT, initially in animals irradiated with high doses of X-rays (7 Gy).
In studies of methods to ameliorate the effect of radiation exposure on the haemopoietic system, comparisons are being made of expansion of murine bone marrow cells using different combinations of HGFs.
Studied at PICR on the effects of in utero exposure of mice to plutonium-239 at 4, 13 or 17 d gestation or direct administration of plutonium-239 to neonatal or weanling progeny have shown life-long deficits in marrow haemopoietic stem cell numbers, though not in mature, functional cell output.
Studies at VITO have shown haemopoietic damage in mice after in utero contamination with americium-241 either by injection on day 14 of gestation or infusion in early or late gestation. The dose to the femur in offspring was estimated as 4 to 20 mGy.
Studies were undertaken at VITO to determine the effect on haemopoietic and stromal stem cells after paternal contamination of BALB/c mice with americium-241 prior to conception.
At UCM, studies of long-term radiation effects on murine stromal cell metabolism and granulocyte function have included in utero X-irradiation at 4 d or 13 d of gestation (1 Gy) and irradiation of adults (5 Gy).
Studies have been conducted at NRPB to compare the effects of haemopoietic progenitor cells of CBA/H mice following low dose x-irradiation (0.5 Gy) at day 7 or day 14 of gestation, and administration of plutonium-239 on day 6 or 13.
A life-span effects study using Balb/c mice had been undertaken at VITO.
Techniques for mapping radon-prone areas
NRPB, NERC, and NPL.RO have studied this subject. NERC chose field study areas to combine a high density of house measurements with geological features typical of Europe. The main controls on radon generation from bedrock were found to be permeability, uranium content with mineralogy. The major rock types giving rise to problems in houses were granites (high uranium content and fracture permeability), limestones (high permeability and dispersed uranium), sandstones (fracture and granular permeability) and shales (if the uranium content is high).
Movement of radon in the ground, into buildings and within buildings
KVI, CSTC/WTCB (BBRI), Risø and SSI contributed in this area of work, KVI used a laboratory facility that consists of a cylindrical vessel (height and diameter 2 m) with measuring probes that allow measurement of pore-water content, air permeability of the soil and radon concentrations at various depths. This was used to study both diffusive and advective radon transport in situations simulating crawl spaces of different heights, with and without forced ventilation and with and without a ground water level in the sand.
Production and transport of radon in building materials
KVI and Bijo contributed in this area. In its second project, KVI studied production and transport of radon in building materials. A set-up was constructed that consists of a stainless steel box closed off with a sealed lid. Inside the box a concrete sample was placed on a steel inner rim, dividing the set-up into two compartments: in the lower compartment a radon source may be placed, the upper compartment is used to detect the transported radon. The sample itself is sealed by treating the side surfaces with an epoxy. The sample is sealed to the inner walls of the set-up by the use of an inflatable tube inside a U-profile. For radon concentration measurements two Lucas cell monitors are used.
CSTC/WTCB (BBRI) and NRPB studied remedial measures. BBRI investigated three dwellings to achieve a better understanding of radon transport and to define the parameters to be measured to allow the choice of appropriate remedial actions.
To investigate remedial measures, NRPB carried out simple radon measurements before and after remediation in a large number of homes which had remedial measures installed. To ensure the collection of high quality data, householders were offered a free measurement of radon provided they completed a questionnaire about the measures installed.
ASQRAD is a flexible tool for displaying the various components of radiation detriment. By incorporating several health effects models, it enables the sensitivity of assumptions made in these models to be investigated. It also allows a wide range of exposure scenarios to be studied and for the user to specify various characteristics of the baseline population, such as its age distribution and cancer rates. The first version of ASQRAD is due to be released around the end of 1995.
Medically Irradiated Populations
Cancer risks among over 14,000 patients irradiated in infancy for skin haemangioma between 1920 and 1959 have been studied at the Karolinska Institute (Sweden). Doses to various organs were estimated, in order to permit dose-response analyses.
At the University of Munich (Germany), the follow-up of 900 patients injected with Ra-224 after World War II mainly for the treatment of tuberculosis and ankylosing spondylitis has been extended to 1995. A total of 26 breast cancers have been observed compared with 7 expected.
Follow-up also continued at GSF (Germany) of a later cohort of about 1500 ankylosing spondylitis patients treated with Ra-224. Seven cases of myeloid leukaemia have been observed in this group, compared with 1.6 expected from regional rates (p=0.001).
Based on just over 1,000 patients in France and the UK given radiotherapy (but not chemotherapy) for a first cancer in childhood, INSERM-U.351 (France) has analysed the second cancer risk in relation to time since exposure.
The incidence of second cancers following treatment for a first cancer in adulthood has been studied at the University of Florence and other treatment centres in central Italy. However, there did not appear to be an association between radiotherapy and the risk of contralateral breast cancer.
Studies of thyroid cancer following medical exposures to iodine have been conducted at the University of Saarland (Germany). Among over 11,000 patients given I-131, 31 cases of thyroid cancer have been identified, compared with about 9-10 expected from regional rates.
Research into the development and application of mechanistic models to cancer data has been performed at NRPB (UK).
Tables of probability of causation for member states of the European Union are at an advanced stage of preparation and, in the case of Germany, are in the course of publication.
A computer algorithm has been developed at the University of Munich to simplify the fitting of risk models to data on populations with protracted exposures.
Risks of childhood leukaemia risks in relation to paternal preconception irradiation (PPI) were analysed at NRPB based on data on the offspring of Sellafield workers and other groups of radiation workers, as well as the A-bomb survivors.
Researchers at Institut Gustave Roussy (France) have extended their study of mortality around French nuclear installations.
Analyses have been conducted of the geographical variation in childhood leukaemia incidence in Great Britain in relation to natural radiation levels and socio-economic status.
Work has progressed at NRPB towards the second analysis of the UK National Registry for Radiation Workers (NRRW). Extra groups of workers have been enrolled into this study and data on follow-up to the end of 1992 are being collected.
Monte Carlo organ dose calculations
Development of these techniques with whole body phantoms able to simulate a wide range of diagnostic x-ray examinations has proceeded in parallel at NRPB and GSF. The two groups have generally adopted the same principles and methods but there are inevitable differences in details related to the particular ways in which their computer codes have been developed over the years and in the intended use of the results.
TNO have used Monte Carlo calculations to estimate coefficients (refereed to as g values in this context) for converting air kerma free-in-air to average glandular tissue dose in the breast for mammography. These calculations use a simplified mathematical model of the breast consisting of a central region surrounded by a superficial layer, both of variable thickness and composition.
TNO has also taken advantage of the mammography x-ray qualities available at the secondary standard calibration laboratory at St George's Hospital to intercompare the calibration of standard mammography dosemeters and kVp meters from the Netherlands and the UK.
St George's Hospital completed studies of the frequency of paediatric x-ray examinations at a sample of London hospitals and collected information on the radiographic procedures adopted during the most common types of examination. This information was passed on to NRPB so that they could select the most appropriate examinations and exposure conditions to model in their Monte Carlo calculations.
Other projects concerned with the optimisation of paediatric radiology included the supply and readout of dosemeters by GSF and NRPB for European trials of a quality criteria document for paediatric radiology being developed by a CEC study group. NRPB and GSF also participated in tow other CEC study groups developing similar sets of quality criteria for common radiographic examinations on adults and for CT examinations on adults. NRPB have drafted sections dealing with patient dosimetry and the derivation of reference doses for the guideline documents being prepared by both of these groups.
Following a review of techniques available, the spectrometer has been developed by NRPB based on a portable sodium iodide detector system weighing less than 15 kg. The design incorporates shielding and collimation so that angular can be measured. The AEA have provided a computer programme to analyse the measured spectra. This programme uses the response function of the sodium iodide crystal to deconvolve the raw, measured spectrum into a photon energy and angle distribution. This data is then used to calculate protection and operational dose quantities in the measured field, using a programme developed at NRPB. The objective of developing a new method of measuring workplace photon spectra has been achieved and measurements have been made in a number of workplaces to demonstrate the technique. These results have been compiled for comparison with other measurements.
The ENEA has carried out a large programme of improvement to its numerical dosimetry capabilities and has installed and commissioned the MCNP and SABRINA codes
Dosemeters from various dosimetry services have been exposed to calibration and simulated workplace radiation fields. The services have then processed the dosemeters and provided their best estimates of dose. The comparison of measured to delivered dose has been made by IPSN, to assess the ability to measure operational quantities in a variety of workplaces.
The first two projects used human lymphocytes irradiated in G(o). The aberration yield was measured immediately following irradiation as well as at later times by the technique of premature chromosomal condensation (PCC) and later at the first metaphase. It is the variation of these effects with radiation quality that is the subject of this report. Particles of approximately constant LET are provided by the accelerator, GANIL, in France. The third project provides the ion beam and measurements of dose for particular irradiations.
The fourth and fifth projects concern the formation of unstable chromosomal aberrations in the first and in subsequent cell cycles following irradiation. Again it was the variation of these effects with radiation quality that formed the basis of these investigations. One group used Chinese hamster ovary cells and a hamster-human hybrid cell line (hamster cells containing a single copy of human chromosome 2). The other group used human fibroblasts. Both of these groups obtained their irradiations from the accelerators at GSI Darmstadt.
Funding SchemeCSC - Cost-sharing contracts
OX11 0RA Didcot
92263 Fontenay Aux Roses
M20 9BX Manchester
00060 Roma - Santa Maria Di Galeria
EH8 9SU Edinburgh
171 77 Stockholm
NG12 5GG Keyworth
2280 HV Rijswijk
6800 ES Arnhem
2300 RA Leiden
171 16 Solna
9747 AA Groningen
OX11 0RA Didcot - Oxfordshire