Use of Monte Carlo calculations and ESR measurements for the physical dose reconstruction of a radiological accident which occurred in Georgia in December 2001.
Isabelle Clairand, François Trompier and Jean-François Bottollier-Depois, IRPA 11, 23-28/06/2004, Madrid (Spain).
Introduction. On December 2nd 2001, three inhabitants of the village of Lia, Georgia, were exposed to two very-high-activity (2.6 1015 Bq) Strontium-90 sources. Following this exposure, the two most affected victims exhibited severe radiological injuries localised in the back as well as a haematopoietic syndrome. The information concerning the distance and the exposure time were not clearly determined. This study deals with the physical dose reconstruction of the accident performed using on the one hand Monte Carlo calculations and on the other hand electron spin resonance (ESR) measurements on a sample of vertebrae removed for medical reasons from one of the two victims treated in France.
Material and methods. The dose reconstruction using numerical simulation was performed using the MCNP Monte Carlo code and a standard anthropomorphic mathematical model. According to clinical observations, each source was supposed to be localized in the middle of the back of the victims at 5 cm from the skin and the dose at the entrance was assumed to be 20 Gy. The ESR measurements on the vertebrae sample were performed using the dose addition method.
Results. The absorbed dose rate in free air in contact with the source is equal to more than 200 Gy.h-1. The depth-dose distribution in the tissue ranges from 20 Gy at the entrance to 1 Gy at 20 cm depth. The absorbed dose is estimated to be 14 Gy at 2 cm depth. The ESR measurements made on the vertebrae sample localized at this level of depth confirm this value; this validates the hypothesis taken concerning the position of the source and the dose at the entrance. The mean dose to the organs is quite heterogeneous and ranges from several mGy to more than 6 Gy (kidneys and adrenals) and the mean absorbed dose to the whole body is around 1.4 Gy.
Conclusion. This work showed the complementarity of the numerical simulation and ESR technique for physical dose reconstruction in case of accidental overexposure. The assessment of the dose received by the victims makes easier the treatment strategy development.