A Case Report: Cytogenetic Dosimetry after Accidental Radiation Exposure during 192Ir Industrial Radiography Testing

The accidental gamma radiation exposure of an industrial radiography worker and the cytogenetic examination of the worker's blood lymphocytes are described here. The exposure of the worker was due to a malfunction at the entrance into the depleted uranium-shielding device of a Ir-192 source during operation. Because the source was sealed no additional beta radiation exposure was assumed. The worker's thermoluminescent dosimeter indicated an absorbed dose of 0.078 Sv, which presumably took place in December 2013. No clinical symptoms were reported in the case history after the potential exposure to radiation. Four months after the incident it was decided that biological dosimetry using dicentric chromosome and micronucleus analysis would be performed to follow radiation protection aspects and to clarify the radiation dose uncertainties for the exposed worker. Micronucleus frequency was not increased above the laboratory's control value of micronucleus background frequency of unexposed individuals. However, the observed dicentric frequency (0.003 dicentric/cell) differs significantly from the laboratory's background level of dicentric chromosomes in unexposed individuals (0.0007 dicentric/cell). Dicentric analysis in 2,048 metaphase cells resulted in an estimated dose of no more than 0.181 Gy (95% upper confidence level), not less than 0.014 Gy (95% lower confidence level) and a mean dose of 0.066 Gy (photon-equivalent whole-body exposure) based on interpolation from the laboratory's calibration curve for Co-60 gamma radiation. Since overdispersion of dicentric chromosomes (u = 9.78) indicated a heterogeneous (partial-body) exposure, we applied the Dolphin method and estimated an exposure of 2.1 Sv affecting 21% of the body volume. Because the overdispersion of dicentric chromosomes was caused by only one heavily damaged cell containing two dicentrics, it is possible that this was an incidental finding. In summary, a radiation overexposure of the radiography worker must be assumed and this case considered as a potential partial-body exposure scenario. (C) 2015 by Radiation Research Society