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.

In vivo measurements of 210Pb in skull and knee geometries as an indicator of cumulative 222Rn exposure in a underground coal mine in Brazil.

Cumulative exposure to radon can be evaluated by measuring 210Pb in bone. The skull and knee are two convenient parts of the skeleton for in vivo measuring 210Pb because these regions of the body present a high concentration of bone, the detectors are easily positioned and the likelihood of cross contribution from other organs or tissues is low. A radiological survey of non-uranium mines in Brazil indicated that an underground coal mine in Paraná, located in the south of Brazil, exhibited a high radon concentration. In vivo measurements of 32 underground coal miners were performed in the IRD-CNEN Whole Body Counter shielded room using an array of four high-resolution germanium detectors. Estimations of 210Pb in the total skeleton were determined from direct in vivo measurements of 210Pb in the head and knees. In vivo measurements of 210Pb in 6 out of 32 underground coal miners ranged from 80 to 164 Bq, suggesting that these workers were significantly exposed to 222Rn.

A physiologically based biokinetic model for cesium in the human body.

A physiologically descriptive model of the biological behavior of cesium in the human body has been constructed around a detailed blood flow model. The rate of transfer from plasma into a tissue is determined by the blood perfusion rate and the tissue-specific extraction fraction of Cs during passage from arterial to venous plasma. Information on tissue-specific extraction of Cs is supplemented with information on the Cs analogues, K and Rb, and known patterns of discrimination between these metals by tissues. The rate of return from a tissue to plasma is estimated from the relative contents of Cs in plasma and the tissue at equilibrium as estimated from environmental studies. Transfers of Cs other than exchange between plasma and tissues (e.g. secretions into the gastrointestinal tract) are based on a combination of physiological considerations and empirical data on Cs or related elements. Model predictions are consistent with the sizable database on the time-dependent distribution and retention of radiocesium in the human body.

The ICRP working party on bioassay interpretation.

In recent years there have been many developments in modelling the behaviour of radionuclides in the human body. The current generation of models is designed to be more 'realistic' than the previous generation of simple compartment models. The International Commission on Radiological Protection (ICRP) uses these models to produce dose coefficients and recognises that there is a need to give more guidance on how these models can be used to interpret bioassay data. A working party has been set up to address the issue. This paper describes some of the problems, some approaches to solving the problems and the progress of the ICRP working party.

NORM workers: a challenge for internal dosimetry programmes.

The mining, milling and processing of uranium and thorium bearing minerals may result in radiation doses to workers. The control of occupational exposures from these natural sources of radiation imposes a challenge to regulators and radiation protection advisers. A survey pilot programme, which included six mines in Brazil and a monazite plant, was established, consisting of the collection and analysis of concentrations of uranium, thorium and polonium in urine, faeces and air samples. Results from workers were compared to background data from their families living in the same area and from residents from the population of Rio de Janeiro. Positive exposure results were identified among the coal miners, the niobium miners and the monazite sand workers. Difficulties in the application of internal dosimetry programmes are discussed in relation to the control of NORM workers.

In vivo measurement technique of 40K as an indicator of the amount of skeletal muscle tissue in the human body.

Potassium is an essential element for human metabolism. It is present in all living cells, predominantly in the skeletal muscle tissue. The energy of the 40K photon and its uniform distribution within the human body allow its in vivo measurement. Subjects of both sexes were monitored at the whole-body counter of the IRD facility for the evaluation of 40K body burden, being divided into two groups: (1) subjects who do not exercise routinely, and (2) subjects who do exercise routinely. The average values found for potassium mass and potassium concentration in group 1 were 99 +/- 17 g of K and 1.3 +/- 0.2 g of K kg(-1) of body mass, respectively, and in group 2 the average values found for potassium mass and potassium concentration were 118 +/- 33 g of K and 1.6 +/- 0.2 g of K kg(-1) of body mass, respectively. The comparison between average values for potassium mass and concentration shows a significant statistical difference.

Retrospective study of the iodine-131 contamination of workers in the radiopharmaceutical industry.

A dose reconstruction study was performed for personnel occupationally exposed to 131I in radiopharmaceutical production, during the years 1981 to 1994, with the objective of estimating committed effective doses and critically reviewing the main causes of their exposures. The workers were selected from a group responsible for the production, labelling and distribution of all radiopharmaceutical material in Brazil. Best estimates of intakes and doses were derived from the examination of the individual monitoring records and the reports from the radiation protection supervisor, complemented by interviews with the workers and with radiation protection officers. Over this time period workers had chronic as well as acute intakes of 131I. Committed effective doses were found to be dependent on the task performed by the worker and the site of operation and inversely correlated with the amounts of iodine handled. Intakes in general were a consequence of inadequate radiation protection control.

Exposure of workers in mineral processing industries in Brazil.

The mining, milling and processing of uranium and thorium bearing minerals may result in radiation doses to workers. A preliminary survey pilot program, that included six mines in Brazil (two coal mines, one niobium mine, one nickel mine, one gold mine and one phosphate mine), was launched in order to determine the need to control the radioactive exposure of the mine-workers. Our survey consisted of the collection and analysis of urine samples, complemented by feces and air samples. The concentrations of uranium, thorium and polonium were measured in these samples and compared to background data from family members of the workers living in the same dwelling and from residents from the general population of Rio de Janeiro. The results from the coal mines indicated that the inhalation of radon progeny may be a source of occupational exposure. The workers from the nickel, gold and phosphate mines that were visited do not require a program to control internal radiological doses. The niobium mine results showed that in some areas of the industry exposure to thorium and uranium might occur.

A biokinetic model for 137Cs.

An improved biokinetic model for 137Cs in humans was developed based on an analysis of data obtained from individuals internally contaminated during an accident in Goiania, Brazil, and other data. Seventeen children (ten girls and seven boys 1-10 y old), ten adolescents (four females and six males), and thirty adults, (fifteen females and fifteen males contaminated in the accident in Goiânia contributed to this study. 137Cs retention was determined through periodic measurements in a whole-body counter. In addition to the data on 137Cs retention from these individuals, data from a study on the metabolism of 137Cs in immature, adult, and aged Beagle dogs and data from the literature were used in the formulation of the 137Cs biokinetic model presented. Mathematically, the retention of cesium is described by three exponential terms, and the retention model is based on a step function of body weight. When the ICRP Publication 56 model for cesium was compared to the model suggested in this paper, it was determined that the ICRP model predicts lower effective doses in 5-y-old children and higher effective doses in infants, adolescents, and adults.

Radiation protection : Medical aspects of the Goiania accident individual monitoring

In September 1987, the rotating asembly of the shielding head of a Teletheraphy unit was removed and the capsule containing 50.9 TBq of 137Cs was dismantled resulting in the widespread contamination of the central Goiania city. This accident resulted in the external and internal exposure of several people, of both genders and of ages ranging from newborn to 73 years old. Sixteen days elapsed between the breaching of the source and the discovery of the accident. During this time, children and adults suffered whole body irradiation and became internally contaminated from eating with contamination hands and from contaminated utensils. People who had handled the source, who lived in houses adjacents to the contaminated sites, or who had some type of contact with the victims were referred to the stadium for monitoring. During the first two months urine and feces analysis was used to evaluate the 137Cs internal contamination and efficacy of PB on 137Cs decorporation. Goiania is located far from any radiationprotection center with the capability to perform in vivo measurements and in vitro monitoring was considering the best technique since most of the individuals had external contamination which would interfere with the in vivo monitoring results

Management of internal contamination accidents

The key to success in managing accidents is the prompt and accurate response of the emergency team. Literature data on the preparation of well conceived emergency plans for the management of internal contamination accidents include among others the following two publications: "The guidebook for the treatment of accidental internal radionuclide contamination of workers", published in Radiation Protection Dosimetry, vol. 41, 1992 and "Assessment and Treatment of External and Internal Radionuclide Contamination", IAEA-TecDoc-869, 1996. Internal contamination by radionuclides occur most likely by inhalation, ingestion or absorption from wounds. The consequences of the contamination depend upon the route of intake, on the physical and chemical properties of the radionuclide and on the amount of activity incorporated. Decisions about the treatment of internally contaminated people should only be made by physicians. The techniques to assess intakes depend on the mode and level of intake, the type and energy of the radiation emitted, the biokinetic of the contaminant and the sensitivity and availability of measurement facilities. In vivo and in vitro techniques are used to quantify internal contamination. This document explains techniques such as In vivo bioassay, In vitro techniques, In vitro bioassay and it discusses about bioassay monitoring techniques, physical samples and interpretation of results

137Cs internal contamination involving a Brazilian accident, and the efficacy of Prussian Blue treatment.

In an accident involving the stealing and breaching of a radiotherapy source in Goiânia, Brazil, 39 individuals had a high level of 137Cs internal contamination. Prussian Blue was used, in doses that varied from 3-10 g d-1 for adults, to enhance the elimination of 137Cs from the body. The total internal committed doses and the effect of Prussian Blue treatment for 15 contaminated adults involved in this accident have been evaluated in this paper. Prussian Blue caused dose reductions in the range of 51-84%, with an average of 71%. This reduction was shown to be independent of the dosage of Prussian Blue. Total internal committed doses were in the range of 4.6 x 10(-3) Gy to 9.7 x 10(-1) Gy for the most-contaminated adults. Data on 137Cs biological half-lives for seven children contaminated in the accident are also presented.

Application of in-vitro bioassay for 137Cs during the emergency phase of the Goiânia accident.

In the Goiânia accident, many individuals suffered external and internal contamination. The screening of internal contamination was done through 137Cs urinary excretion. During the first month after the accident, only in-vitro bioassay procedures were done. Incorporation into the body and committed doses were estimated using age-specific mathematical models correlating these quantities to the 137Cs excreted in urine. The ratio of feces to urine of 137Cs excretion was used to evaluate the effectiveness of the administration of Prussian Blue on removal of 137Cs from the body.

Studies of Cs retention in the human body related to body parameters and Prussian blue administration.

Using the in-vivo monitoring data from the individuals that suffered internal contamination in the Goiânia accident, a preliminary study on the elimination of Cs from their body was conducted. It was concluded that elimination follows a first-order linear kinetic pattern, both with and without Prussian Blue treatment. Cesium half-lives for both sexes were shown to be influenced mainly by the weight of each individual. In general, Prussian Blue seems to reduce the half-life by 32%. At the time our study was conducted, patients who were under treatment with the drug were receiving 3 g d-1, 6 g d-1, or 10 g d-1 of the medication. Our results suggest that there is an optimum dosage for a certain weight range to achieve this reduction in half-life, but one would need more data to statistically prove this assumption.