This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal exposures are characterized by a spatially inhomogeneous irradiation of the body, which is potentially prolonged over large periods and variable over time, is particularly problematic for biological and electron paramagnetic resonance (EPR) dosimetry methods when compared with external exposures. The paper gives initially specific information about internal dosimetry methods, the most common cytogenetic techniques used in biological dosimetry and EPR dosimetry applied to tooth enamel. Based on real-case scenarios, dose estimates obtained from bioassay data as well as with biological and/or EPR dosimetry are compared and critically discussed. In most of the scenarios presented, concomitant external exposures were responsible for the greater portion of the received dose. As no assay is available which can discriminate between radiation of different types and different LETs on the basis of the type of damage induced, it is not possible to infer from these studies specific conclusions valid for incorporated radionuclides alone. The biological dosimetry assays and EPR techniques proved to be most applicable in cases when the radionuclides are almost homogeneously distributed in the body. No compelling evidence was obtained in other cases of extremely inhomogeneous distribution. Retrospective dosimetry needs to be optimized and further developed in order to be able to deal with real exposure cases, where a mixture of both external and internal exposures will be encountered most of the times.
Mr Litvinenko died on 23 November 2006 after having been poisoned with polonium-210 on 1 November. Measurements of the polonium-210 content of post-mortem tissue samples and samples of urine and blood showed the presence of large amounts of Po. Autoradiography of hair samples showed two regions ofPo activity, providing evidence of an earlier poisoning attempt during October 2006, resulting in absorption to blood of about one-hundredth of that estimated for 1 November. Intake by ingestion on 1 November was estimated to be around 4 GBq, assuming 10% absorption to blood, and the resulting organ doses reached estimated values that were generally in a range from about 20 Gy to over 100 Gy. Comparison with estimates of protracted alpha particle doses required to cause irreversible organ damage supported the conclusion that death was the inevitable consequence of multiple organ failure, with destruction of the haemopoietic bone marrow, as well as damage to kidneys and liver, being important contributors. If the earlier poisoning during October 2006 had not been followed by a second major intake on 1 November, it is possible that the earlier intake of around 40 MBq, with absorption of 4 MBq to blood, might have caused irreversible kidney damage over a prolonged period of months or years, with doses of approaching 3 Gy.
In the event of a radiation emergency, people close to the site of the incident may be exposed to radiation by external exposure, or as a result of intakes of radioactive material. For these incidents it may be necessary to monitor members of the public both for external and internal contamination. This work reviews currently available equipment for the assessment of internal exposure following an emergency. It concentrates on incidents involving the spread of radioactive material and on contamination by radionuclides which emit penetrating radiation. It is essential that this monitoring is carried out as soon as possible so that people who have been exposed at a level which could have an effect on health can be identified and receive prompt medical assessment. Proposed action levels to identify people who need medical attention are reviewed to determine the required sensitivity of monitoring equipment. For releases containing gamma-ray emitting radionuclides the best means of measuring internal contamination is to use detectors placed close to the body (whole body or partial body monitoring). Laboratory based whole body monitors could be used but these may well be inconveniently located and so equipment which can be deployed to the site of an incident has been developed and these are described. The need for rapid selection and prioritisation of people for monitoring, methods to deal with potentially high numbers of contaminated people and the requirement for a means of rapidly interpreting monitoring information are also discussed.It has been found that for many types of incidents and scenarios, systems based on unshielded high-resolution detectors and hand-held instruments do have the required sensitivity to identify people who require medical assessment.
This paper summarises a comprehensive review of radio-analytical data from autopsy, whole or partial body monitoring and the assay of teeth, foetuses and urine for non-occupationally exposed members of the public in the UK between 1957 and 2003. Most attention has been given to measurements of artificial radionuclides formed in the nuclear fuel cycle, uranium and thorium. The review concentrates on measurements on people in the UK who live or have lived in the vicinity of nuclear power sites. When UK data are unavailable, or for the purposes of comparison, information has been included from studies in other countries. Highlights of key findings of the document are listed: The concentrations of strontium-90 in bone and teeth have reflected changes in the amounts present in the environment due to fallout from nuclear testing. There are higher concentration levels of 239+240Pu in samples from West Cumbria compared with the rest of the UK. However, the levels are so low that any increase in risk of induced skeletal tumours (including leukaemia) would be very small compared with those arising from the intake of natural radionuclides. As expected there have been only a few published autopsy studies. Both tissue sample mass and radionuclide concentrations were low, leading to relatively large measurement uncertainties. Whole body measurements of 137Cs in residents in Berkshire and Oxfordshire clearly show the effect of atmospheric testing of nuclear weapons and of the Chernobyl accident. A survey of whole body 137Cs and 134Cs content following the Chernobyl accident showed that residents of Central Scotland, North-West England and North Wales had twice the radiocaesium content of residents in the rest of England and Wales. Measurements of 131I in the thyroid have been reported following the accidents at Windscale and Chernobyl for most regions of the UK. Few excretion studies have been reported although this does not diminish their importance. One study on the urinary excretion rate of 90Sr in adults and children living in the Dounreay area suggested that the results did not support this radionuclide as being the cause of increased childhood leukaemia. Similar conclusions were drawn from another study involving the assay of 239Pu. It is suggested that a national database of measurements made on members of the public should be initiated. The database would provide a means for identifying future trends.
The part played by individual monitoring within the context of the overall response to incidents involving the malevolent use of radiation or radioactive material is discussed. The main objectives of an individual monitoring programme are outlined, and types of malevolent use scenario briefly described. Some major challenges facing those with responsibilities for planning the monitoring response to such an incident are identified and discussed. These include the need for rapid selection and prioritisation of people for individual monitoring by means of an effective triage system; the need for rapid initiation of individual monitoring; problems associated with monitoring large numbers of people; the particular difficulties associated with incidents involving pure-beta and alpha-emitting radionuclides; the need for techniques that can provide retrospective estimates of external radiation exposures rapidly and the need for rapid interpretation of contamination monitoring data. The paper concludes with a brief review of assistance networks and relevant international projects planned or currently underway.
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