Videoscopic assessment of the maintenance status of gamma radiography exposure containers employed in Brazil.

Industrial radiography is the most frequent method of non-destructive testing (NDT) used by Brazilian industrial facilities for investigating the material integrity of a test object. In Brazil, industrial radiography employs around 220 x-ray and 290 gamma radiography machines. About 90% of the latter uses iridium ((192)Ir) sources. The large majority of (192)Ir projectors in operation in Brazil have been in continuous usage for more than 25 years, which means that they are old and worn-out. Usually the majority of accidents concerning gamma radiography occur during the return of the source into the exposure container. Poor maintenance or imperfections of the internal channel of the exposure container can lead to accidental source exposure. In the present work the internal tube of 65 gamma machines from nine Brazilian companies that render gamma radiography services were analysed using an industrial videoscope. The internal images from the projectors were compared with the internal image of an apparatus that had never been used, i.e. has never received a radioactive source. From the 65 machines evaluated, nine showed irregularities of the internal tube. It was also observed that each company follows a different methodology for the maintenance and lubrication of the exposure containers and drive cables.

Dose reconstruction of a Brazilian industrial gamma radiography partial-body overexposure case.

In May 2000, an operator of a (60)Co industrial gamma radiography apparatus, during a routine service, was involved in a partial-body radiological accident, which caused serious injuries to his left hand. Dose reconstruction was started aiming to assess the radiation doses, in order to assist the medical staff in the evaluation and prescription of suitable medical procedures for the patient's treatment and follow-up. This work presents the dose reconstruction used for assessment of the distribution of doses on the patient's left hand, which was made using two methods: physical and computational techniques. For the first technique a physical hand simulator was built. The computational method was performed using microcomputer software for external dose calculations, named 'Visual Monte-Carlo-VMC', together with a hand voxel simulator. The values obtained through both methods for the distribution of absorbed doses on the operator's left hand were compared. About half of them were similar within a range of uncertainty of 20%.

Radiological safety assessment of Brazilian industrial facilities with electron accelerators.

Industrial electron accelerators are used by eight installations in Brazil, with a total of 14 machines generating electron beams. These facilities are classified into categories I or II, according to the International Atomic Energy Agency (IAEA) system. In category I are included the facilities with an integrally shielded unit with interlocks, where human access during operation is not physically possible owing to the configuration of the shielding. In category II are included the facilities with a unit housed in a shielded room that is kept inaccessible during operation by an entry control system. Of the 14 accelerators operational in Brazil, 11 belong to category I and three to category II. In the present work a methodology for the assessment of the radiological safety of these accelerator facilities was developed and applied, mainly on the basis of specific recommendations from the IAEA. The main safety items were evaluated at those eight installations. According to the results obtained here, no inadequacies were observed at the three installations in category II, from the radiological safety and radioprotection points of view. Nevertheless, two out of the five installations in category I showed several deficiencies. Most of these inadequacies have been corrected during this work, and the rest are in the course of being corrected.

Conventional radiation-biological dosimetry using frequencies of unstable chromosome aberrations.

Frequency of chromosome aberrations detected by conventional cytogenetics is a very useful parameter in biological radiodosimetry. It can be used for estimating absorbed doses in individuals working with radioactive sources and individuals accidentally exposed to radiation. In the first case subjects wear physical dosimeters as a routine safety habit. Our laboratory at the Institute of Radioprotection and Dosimetry (IRD, Brazil) has been using conventional cytogenetic analysis to complement data obtained by physical dosimetry since 1983. Until now, we have investigated more than one hundred cases where individual physical dosimeters detected occupational exposure (above the safety limits allowed). In total, only 34% of these cases were confirmed by conventional cytogenetic dosimetry. We have also used conventional cytogenetic analysis following the radiation accident of Goiania (Brazil) in 1987. Peripheral lymphocytes from 129 exposed or potentially exposed individuals were analyzed for the frequencies of unstable chromosomal aberrations (dicentrics, centric rings and acentrics fragments) to estimate absorbed radiation doses. During the emergency period, doses were estimated to help immediate medical treatment using in vitro calibration curves produced before the accident. Later on, doses were assessed once more using new in vitro calibration curves. A drawback of this technique is that unstable aberrations are lost after exposure. To investigate the mean lifespan of lymphocytes containing dicentric and ring aberrations, we have followed 15 victims of the Goiania accident over all these years. Results suggest that the disappearance of unstable aberrations is dose-dependent. This could explain the variation in the results found among studies in this field.

137Cesium-induced chromosome aberrations analyzed by fluorescence in situ hybridization: eight years follow up of the Goiânia radiation accident victims.

The radiation accident in focus here occurred in a section of Goiânia (Brazil) where more than a hundred individuals were contaminated with 137Cesium on September 1987. In order to estimate the absorbed radiation doses, initial frequencies of dicentrics and rings were determined in 129 victims [A.T. Ramalho, PhD Thesis, Subsidios a tecnica de dosimetria citogenetica gerados a partir da analise de resultados obtidos com o acidente radiologico de Goiânia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, 1992]. We have followed some of these victims cytogenetically over the years seeking for parameters that could be used as basis for retrospective radiation dosimetry. Our data on translocation frequencies obtained by fluorescence in situ hybridization (FISH) could be directly compared to the baseline frequencies of dicentrics available for those same victims. Our results provided valuable information on how precise these estimates are. The frequencies of translocations observed years after the radiation exposure were two to three times lower than the initial dicentrics frequencies, the differences being larger at higher doses (>1 Gy). The accuracy of such dose estimates might be increased by scoring sufficient amount of cells. However, factors such as the persistence of translocation carrying lymphocytes, translocation levels not proportional to chromosome size, and inter-individual variation reduce the precision of these estimates.

Current cytogenetic methods for detecting exposure and effects of mutagens and carcinogens.

Most mutagens and genotoxic carcinogens are efficient inducers of chromosomal alterations in exposed cells. Two important classes of aberrations, namely structural and numerical, are recognized and both types of aberrations are associated with congenital abnormalities and neoplasia in humans. These alterations can be easily detected and quantified in human peripheral blood lymphocytes. Conventional staining techniques can be used to detect these aberrations; this technique was used to estimate absorbed dose in the case of a radiation accident in Goiania, Brazil. A recently introduced fluorescent in situ hybridization technique (FISH) using DNA probes has increased the sensitivity and ease of detecting chromosome aberrations, especially stable chromosome aberrations. This technique allows, to some extent, the estimation of absorbed radiation dose from past exposures. Numerical aberrations can be directly estimated in metaphases by counting the number of FISH-painted chromosomes. Micronuclei are formed by lagging chromosome fragments or whole chromosomes during the anaphase stage of cell division. The nature of micronuclei as to whether they possess a centromere can be determined either by CREST staining (calcinosis, Raynoud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia) or FISH with centromere-specific DNA probes. In several carcinogen-exposed populations, such as heavy smokers or people exposed to arsenic, aneuploidy appears to be more common than structural aberrations. In victims of radiation accidents, aneuploidy (hyperploidy) has been found to be common in addition to structural aberrations.

Lifespan of human lymphocytes estimated during a six year cytogenetic follow-up of individuals accidentally exposed in the 1987 radiological accident in Brazil.

Following the radiological accident which occurred in the city of Goiania (Brazil), in September 1987, a cytogenetic follow-up of 15 exposed patients was started, aiming to observe the mean lifetime of lymphocytes containing dicentric and ring aberrations. The results suggest that the disappearance rate of unstable aberrations follows a two-term exponential function. Up to 470 days after exposure, there is a rapid fall in the aberration frequency. After 470 days, the disappearance rate is very slow. These results may reflect different subpopulations of human lymphocytes, with different lifespans. The estimated average half-time of elimination of dicentrics and rings among the highly exposed group (doses above 1 Gy) was 110 days for the initial period after the exposure (up to 470 days). This value is significantly shorter than the usually accepted value of 3 years reported in the literature. Statistical analysis of possible correlations between the individual half-times and biological parameters, such as sex, age, leukopenia level shown during the critical period, absorbed dose (initial frequency of chromosomal aberrations) and the administration of the bone marrow stimulating factor (rHuGM-CSF) was performed. None of these parameters showed a correlation with the half-time of disappearance of chromosomal aberrations. For the individuals who had received less than 1 Gy the disappearance of aberrations was slower, with a half-time of 160 days during the period up to 470 days after exposure. Mean disappearance functions of unstable chromosome aberrations were inferred, to be applied in accident situations in which there is a blood sampling delay.

Intercomparison in cytogenetic dosimetry among five laboratories from Latin America.

As part of a regional International Atomic Energy Agency (IAEA) collaborative project within Latin America, five countries participated in an intercomparison in cytogenetic dosimetry. Coded slides for chromosomal aberrations and micronucleus analyses were prepared by the coordinator laboratory which organized the exercise and sent to the other participating laboratories. For estimates of dose, each laboratory scored the frequency of dicentrics in metaphases and the frequency of micronuclei in binucleated cells. The lymphocytes were irradiated with 60Co gamma-rays (0, 0.75, 1.5 and 3.0 Gy). Eleven of the 15 estimates of dose based on dicentrics and nine of the 12 based on micronuclei fell within +/- 30% of the true dose. When considering the uncertainties of the dose estimates, the true dose fell within the 95% confidence limits of the estimates on eight of the 15 occasions for dicentrics and four of the 12 for micronuclei.

Frequency of chromosomal aberrations in a subject accidentally exposed to 137Cs in the Goiania (Brazil) radiation accident: intercomparison among four laboratories.

After the Goiania radiation accident which occurred in Brazil in September 1987, an intercomparison was performed to determine whether different cytogenetic laboratories would score similar frequencies of chromosomal aberrations in cultures of lymphocytes of a highly exposed patient. For this purpose 2 chromosome slides from the subject were scored by 4 laboratories in total. The results were consistently close and confirmed the high frequency of chromosome-type aberrations observed initially in the patient.

Measurements of 137Cs in blood from individuals exposed during the Goiânia accident.

Blood samples of some highly internally contaminated Goiânian patients were measured for 137Cs activity. The distribution of activity among the blood components was checked. We found that the majority of the activity was confined to the cellular fraction, mainly to the erythrocytes (red cells).