MEDOR, a didactic tool to support interpretation of bioassay data after internal contamination by actinides.

A didactic software, MEthodes DOsimètriques de REférence (MEDOR), is being developed to provide help in the interpretation of biological data. Its main purpose is to evaluate the pertinence of the application of different models. This paper describes its first version that is focused on inhalation exposure to actinide aerosols. With this tool, sensitivity analysis on different parameters of the ICRP models can be easily done for aerosol deposition, in terms of activity and particle number, actinide biokinetics and doses. The user can analyse different inhalation cases showing either that dose per unit intake cannot be applied if the aerosol contains a low number of particles or that an inhibition of the late pulmonary clearance by particle transport can occur which contributes to a 3-4 fold increase in effective dose as compared with application of default parameters. This underlines the need to estimate systematically the number of deposited particles, as well as to do chest monitoring as long as possible.

Radiotoxicological intercomparisons organised by the Commissariat à l'Energie Atomique group in France.

People working in French nuclear plants are monitored either by whole body counting or by the measurement of biological samples. The radiochemical and radiometric procedures used have to be periodically reviewed. A working group, including practising biologists from CEA, EDF and the Armed Forces Health Service, instituted comparisons of radiotoxicological test assessments. Since 1978, about 60 intercomparisons have been made. Currently 30 European laboratories are involved in these intercomparisons. This paper provides a brief history of the intercomparison exercises, describes the logistics of sample collection and preparation, and presents the results, showing the position of each laboratory in relation to the reference and median values. Diagrams produced by radiochemical analysis, relating to plutonium in urine and in faecal samples, and to tritium, strontium and enriched uranium in urine, are analysed.

Assessment of radioactive systemic uptakes by deconvolution of individual monitoring results.

The methods of interpretation presently available for evaluating individual radioactivity intakes from measured data involve difficulties connected with the adaptation of metabolic models to the situations encountered in practice. These difficulties essentially concern the definition of appropriate parameters for each encountered case, and very often- except for characterized incidents-erroneous appreciation of the time course of contamination episodes and of th routes of entry. These considerations led us to develop a simplified method of interpreting monitoring data, by considering separately the data relating to routes of entry and those concerning systemic contamination, i.e., the contamination occurring after the transfer of radionuclides to the blood. An approach to interpreting measurements of systemic contamination is proposed in this study. This method is to calculate, from these measurements, the values for the activity absorbed daily from the routes of entry into the blood using the appropriate retention and excretion functions. a day-to-day follow-up of the absorbed activity becomes possible, thus enabling its real-time evolution to be recorded and easy to consult. A few applications of the method are described, including cases of acute tritium and uranium contamination and of chronic contamination by tritium, uranium, and iodine. The conditions and constraints required to validate the proposed approach are indicated.

Biokinetic modelling of DTPA decorporation therapy: the CONRAD approach.

Administration of diethylene triamine pentaacetic acid (DTPA) can enhance the urinary excretion rate of plutonium (Pu) for several days, but most of this Pu decorporation occurs on the first day after treatment. The development of a biokinetic model describing the mechanisms of decorporation of actinides by administration of DTPA was initiated as a task of the coordinated network for radiation dosimetry project. The modelling process was started by using the systemic biokinetic model for Pu from Leggett et al. and the biokinetic model for DTPA compounds of International Commission on Radiation Protection Publication 53. The chelation of Pu and DTPA to Pu-DTPA was treated explicitly and is assumed to follow a second-order process. It was assumed that the chelation takes place in the blood and in the rapid turnover soft tissues compartments of the Pu model, and that Pu-DTPA behaves in the same way as administered DTPA. First applications of this draft model showed that the height of the peak of urinary excretion after administration of DTPA was determined by the chelation rate. However, repetitions of DTPA administration shortly after the first one showed no effect in the application of the draft model in contrast to data from real cases. The present draft model is thus not yet realistic. Therefore several questions still have to be answered, notably about where the Pu-DTPA complexes are formed, which biological ligands of Pu are dissociated, if Pu-DTPA is stable and if the biokinetics of Pu-DTPA excretion is similar to that of DTPA. Further detailed studies of human contamination cases and experimental data about Pu-DTPA kinetics will be needed in order to address these issues. The work will now be continued within a working group of EURADOS.

Inhaled particle deposition and clearance from the normal respiratory tract.

Tracheo-bronchial and pulmonary deposited fractions of inhaled insoluble particles and their clearances rates were studied in 16 healthy non-smokers. After oral inhalation of radioactive particles (Mean Mass Aerodynamic Diameter (MMAD) = 3 microns, sigma g = 1.4 labelled with 111In) incorporated radioactivity was measured for each subject both by a gamma camera from to until the 3rd day, then from the 3rd until the 5th day first by a gamma camera and then by a low background profile scanner and from the 5th until the 35th day by a low background profile scanner alone. Clearance rates were calculated from the biological half lives of the deposited tracers. All subjects performed respiratory function tests. Experimental data were fitted to a two-compartment exponential system with two biological half lives: T1 = 76 min for 30%, T2 = 3.15 days for 40% of the deposited material. The delayed clearance phase for the remaining 30% of the deposited material approaches a constant rate. Our clearance values were compared with those of the Task Group of Lung Dynamics (T.G.L.D.) and other authors' results, especially for T1 and T2. These values are analyzed in terms of mucus velocity and mucociliary transport in distal conductive airways. Impaired transport reduces natural defenses and increases toxicological hazards. Therefore reliable techniques for detecting such impairment may be important in evaluating pulmonary involvement in environmental respiratory disease.