A radiation accident involving a caesium-137 therapy source in Goiania (Brazil) in September 1987 resulted in over 50 patients being exposed to moderate to high doses (0.2-7 Gy) of gamma radiation. Cytogenetic techniques (ie frequencies of dicentrics and rings in peripheral lymphoctes) were employed to estimate the absorbed radiation dose. The follow up study extending over more than one year, indicated a decline in the frequency of dicentric carrying lymphocytes, with an average half life of about 130 days, much lower than other published estimates.
Using chromosome specific biotinylated library probes for chromosomes 1, 2, 8 and 19, the frequencies of chromosomal translocations and deletions as well as the incidence of anenploidy in the lymphocytes of exposed individuals were determined. In some cases there was a significant increase in the frequency of translocations and anenploidy which was not dose dependent. Some of the translocation bearing lymphocytes appeared to be of clonal origin exhibiting the same translocation. The frequencies of hypoxanthine phosphonbosyltransferase (HPRT) mutations in lymphocytes and of hemoglobin mutations were determined and in both cases, some individuals showed an increase of 2 to 50 fold in mutant frequencies in comparison to unexposed controls.
In an accident involving the destruction of a 137Cs source (1325 Ci) in Goiania, Brazil in September 1987, several individuals were exposed to gamma radiation, mainly externally and some internally. In collaboration with the Institute of Radiation Protection and Dosimetry (IRD), Rio de Janeiro, we have made dose estimates for exposed individuals by biological dosimetry using the frequencies of chromosomal aberrations.
There are 32 individuals exposed to radiation doses of 0.5 Gy to 7.0 Gy, of these three had mainly internal exposure. The present study is aimed at following up this exposed population in collaboration with IRD in Rio. The following parameters will be studied:
frequency of unstable chromosome aberrations and micronuclei as well as their statistical distribution will be determined periodically (every four months) in individuals exposed to 0.5 Gy and above;
frequency of stable aberrations will be followed by banding techniques in the same population;
mutations in the HPRT locus will be determined in these individuals and if enough blood samples become available, mutants will be isolated and cloned for further sequencing of the mutants;
mutant frequency in 3 different loci of the beta chain of haemoglobin will be measured in these individuals with parallel controls.
The determination of mutant frequencies will be made once a year.