Biomedical subjects

D R Melo

Publications and source records attributed to D R Melo.

8 recordsLinked to original sources

PubMed2003

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.

Cesium↗

PubMed2003

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.

Administration, Inhalation↗

PubMed2003

Requirements for authorisation of internal dosimetry services.

In order to ensure that a facility is in compliance with the occupational exposure requirements established by regulatory authorities, the measurements and dose assessments specified in the individual monitoring programme need to be reliable. There are two important questions that shall be addressed here: one is how the licensed facilities can demonstrate to their workers and regulatory bodies compliance with the regulatory limits and the reliability of the results of the individual monitoring programmes; the other concerns the mechanisms used to demonstrate to a facility in another country the reliability of the measurement results of an individual monitoring bioassay programme. The accreditation of the bioassay laboratory, according to ISO/IEC 17025, shall be the basic requirement for obtaining the authorisation granted by the national regulatory authority. For the second question, such confidence can be achieved through International Laboratory Accreditation Cooperation (ILAC).

Certification↗

PubMed2001

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.

Brazil↗

PubMed1997

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.

Adolescent↗

PubMed1996

Prussian Blue decorporation of 137Cs in beagles of different ages.

A 6-wk study was conducted using immature (4.7 mo), young adult (2.4 y), and aged (13.5 y) male beagles to determine the modifying effect of age on the effectiveness of Prussian Blue decorporation therapy for the removal of injected 137Cs. Whole-body clearance rates for injected 137Cs decreased with increasing age in the dogs. Treatment with Prussian Blue changed the ratio of fecal to urinary 137Cs excretion from 0.8 in untreated dogs to 2.2 in treated animals. The 137Cs concentrations in tissues of untreated and Prussian Blue-treated dogs at the end of the 6-wk study were similar, with the greatest concentrations in the skeletal muscle tissue, spleen, and kidneys. There was a lower concentration of 137Cs in the livers of the treated dogs. The reductions in the average total whole-body doses resulting from Prussian Blue treatment during the course of this study were 51% in the immature, 31% in the young adult, and 38% in the aged dogs. Because of the differences in the intake of Prussian Blue by the dogs in the different groups relative to their body weight, it is unclear as to the relative effectiveness of Prussian Blue in dogs of different ages.

Age Factors↗

PubMed1994

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.

Accidents↗

PubMed1991

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.

Accidents↗