Efficacy of Prussian blue on 137Cs decorporation therapy

Prussian blue (PB) is an efficient drug for enhancing cesium elimination from the body. Literature data on the efficacy of PB treatment in dosages that vary from 1-10 g d was reviewed. Cesium biokinetics was simulated using a detailed systemic biokinetic model. The same model was used to simulate the maximum action of PB by interrupting the enterohepatic circulation. Model results reproduced reasonably well the literature data on the efficacy of PB administered to humans after incidental cesium intakes, as well as results from animal experiments. Maximum efficiency of the reduction of the long-term half-time is obtained with the administration of 3 g d PB to the adult. Maximum efficiency of reducing the Cs body burdens is obtained when PB is administered on the first day after the intake, due to the increase of the short-term elimination of cesium. The model predicts that reduction of the long-term half-life is not affected by the time after intake that PB is administered, as long as it is given within the interval from 1 h to 1 y after the intake.

Uncertainties in internal doses calculated for Mayak workers--a study of 63 cases

This study makes use of 63 cases of Mayak workers exposed to Pu-239 with autopsy data and some late-time urine bioassay data. In addition, air-concentration data--used to construct monthly average values--are available for each case, which provide the time dependence and potential magnitudes of normal inhalation intakes for each case. The purpose of the study is to develop and test Bayesian methods of dose calculation for the Mayak workers. The first part of the study was to quantitatively characterise the uncertainties of the bioassay data. Then, starting with three different published biokinetic models, the data are fit by varying intake and model perturbation parameters, e.g., parameters influencing the lung, thoracic lymph nodes, liver and bone retention. Statistical self-consistency arguments are used to check the measurement uncertainty parameters within the Poisson-lognormal model. The second part of the study is to set up and test Bayesian dose calculations, which use the point determinations of biokinetic parameters from the study cases within a discrete, empirical Bayes approximation. The main conclusion of the study is that these methods are now ready to be applied to the entire Mayak worker population.

IMPDOS (improved dosimetry and risk assessment for plutonium-induced diseases): internal dosimetry software tools developed for the Mayak worker study

A collection of software tools developed for the Mayak worker study is described. IMPDOS is software for modelling, data analysis, and activity and dose calculations using the bioassay and postmortem data from Mayak workers provided by Southern Urals Biophysics Institute. The capabilities include: parameter fitting of data for individual cases, Bayesian dose calculations using the fit results for collections of cases with extensive data as a biokinetic prior, and database storage of results for retrieval, analysis and interpretation.

A study of early Los Alamos internal exposures to plutonium

Internal dose caused by exposure to (239)Pu/(240)Pu is calculated for a group of 210 former Los Alamos workers who participated in the urine bioassay programme during the years 1944-45. An iterative Bayesian procedure is employed, where the distribution of intake amounts resulting from an initial calculation is used to define a prior probability distribution of inhalation intakes for an iterated second calculation. The urine bioassay data from this time period were not of high quality, and the more accurate intake prior tempers the effect of spurious high samples, which were probably caused by sample contamination.

Worldwide bioassay data resources for plutonium/americium internal dosimetry studies

Biokinetic models are the scientific underpinning of internal dosimetry and depend, ultimately, for their scientific validation on comparisons with human bioassay data. Three significant plutonium/americium bioassay databases, known to the authors, are described: (1) Sellafield, (2) Los Alamos and (3) the United States Transuranium Registry. A case is made for a uniform standard for database format, and the XML standard is discussed.

Efficacy of 3,4,3-LI(1,2-HOPO) for decorporation of Pu, Am and U from rats injected intramuscularly with high-fired particles of MOX

This study aimed to assess the efficacy of 3,4,3-LI(1,2-HOPO) for reducing uranium, plutonium and americium in rats after intramuscular injection of (U-Pu)O2 particles (MOX). Sixteen rats were contaminated by intramuscular injection of a 1 mg MOX suspension and then treated daily for 7 d with LIHOPO (30 or 200 micromol kg(-1)) or DTPA (30 micromol kg(-1)). LIHOPO was inefficient for removing Pu, Am and U from the wound site. However, it reduced Pu retention in carcass and liver by factors of 2 and 6 respectively, and Am retention in carcass and liver by factors of 10 and 30. In contrast, the effect of LIHOPO on U was to decrease the retention in kidneys by a factor of 75. These results confirm that LIHOPO is a good candidate for use after contamination with MOX, in combination with localised wound lavage or surgical treatment aimed at removing most of the contaminant at the wound site.

Internal dosimetry of uranium isotopes using Bayesian inference methods

A group of personnel at Los Alamos National Laboratory is routinely monitored for the presence of uranium isotopes by urine bioassay. Samples are analysed by alpha spectroscopy, and the results are examined for evidence of an intake of uranium. Because the measurement uncertainties are often comparable to the quantities of material we wish to detect, statistical considerations are crucial for the proper interpretation of the data. The problem is further complicated by the significant, but highly non-uniform, presence of uranium in local drinking water and, in some cases, food supply. Software originally developed for internal dosimetry of plutonium has been adapted to the problem of uranium dosimetry. The software uses an unfolding algorithm to calculate an approximate Bayesian solution to the problem of characterising any intakes which may have occurred, given the history of urine bioassay results for each individual in the monitored population. The program uses biokinetic models from ICRP Publications 68 and later, and a prior probability distribution derived empirically from the body of uranium bioassay data collected at Los Alamos over the operating history of the laboratory. For each individual, the software creates a posterior probability distribution of intake quantity and solubility type as a function of time. From this distribution, estimates are made of the cumulative committed dose (CEDE) to each individual. Results of the method are compared with those obtained using an earlier classical (non-Bayesian) algorithm for uranium dosimetry. We also discuss the problem of distinguishing occupational intakes from intake of environmental uranium, within a Bayesian framework.

Review of methods and computer codes for interpretation of bioassay data

Internal dose determination is an essential component of individual monitoring programmes for workers or members of the public exposed to radionuclides, and methods and computer programs are required for dose assessment. A recent international European Radiation Dosimetry Group (EURADOS) intercomparison has shown unacceptably large ranges in the results assessment. An ICRP working party has been initiated to consider what guidance ICRP can give on the use of models and interpret bioassay data in terms of intake/dose. In this field, six codes for bioassay data interpretation, which implement the current ICRP publication 78 biokinetic models, have been reviewed against several criteria with different levels of importance: minor criteria such as the practical use of the code and the graphical capabilities, and major criteria such as the choice of available parameters, peculiarities of data fitting and interpretation, the choice of biokinetic models and the use of uncertainties. All these criteria were assessed using one artificial set of data and two examples extracted from the previous international EURADOS intercomparison.

The application of Bayesian techniques in the interpretation of bioassay data

The inverse problem of internal dosimetry is naturally posed as a problem of Bayesian inference. The Bayesian approach is of practical importance in three areas: (1) avoiding false positives in the detection of rare events, (2) the calculation of uncertainties, and (3) the calculation of multiple intakes, all of which are important for internal dosimetry. In this paper, the Bayesian approach to the interpretation of measurements is first reviewed using a simple conceptual example. Then, a simple 239Pu case using IMBA expert is discussed, and finally a current cutting-edge example is discussed involving real 238Pu data calculated with a Markov Chain Monte Carlo algorithm and with exact calculation of poisson likelihood functions.

Bayesian internal dosimetry calculations using Markov Chain Monte Carlo

A new numerical method for solving the inverse problem of internal dosimetry is described. The new method uses Markov Chain Monte Carlo and the Metropolis algorithm. Multiple intake amounts, biokinetic types, and times of intake are determined from bioassay data by integrating over the Bayesian posterior distribution. The method appears definitive, but its application requires a large amount of computing time.

Biological effects of the enhanced excretion of zinc after calcium diethylenetriaminepentaacetate chelation therapy

An enhanced, uncompensated excretion of zinc may be responsible for unwanted side-effects that could develop after prolonged chelation therapy with calcium diethylenetriaminepentaacetate (Ca-DTPA). As a preliminary means of defining "potential toxicity" within this hypothesis, the "normal" concentration range of Zn++ excreted in the urine of three adult female baboons was measured on a daily basis; changes in urinary Zn++ excretion were then quantitated as a function of the injection time and dose of the chelating agent Na3(Ca-DTPA) originally administered to enhance the excretion of 241Am from the body. In addition, the inhibitory action of the chelator compound on the activity of a specific metalloenzyme system, erythrocytic aminolevulinic acid dehydratase (ALAD), which requires Zn++ as a co-factor, has been determined as a measure of a specific biological effect. It was found that whenever the concentration of Zn++ in urine was above 2 mug/ml (or greater than approximately four times the "normal" urinary excretion level), the activity of ALAD dropped below 250 nmol PBG/ml RBC/hr or approximately one-half the mean "normal" activity value for this primate species.