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Dose reconstruction using numerical tools in the case of accidental exposure to ionizing radiation


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Clairand I, Bottollier-Depois J-F., Gaillard-Lecanu E., Roux A., Trompier F. et Renon X Phys Med 2001;17(2). 40th annual meeting of the Société Française de Physique Médicale, Nantes (France), June 6-8, 2001

Résumé

Introduction: In the case of overexposure to ionizing radiation, clinical observations as well as biological and physical dosimetric investigations are usually taken into account to estimate the seriousness of the irradiation. The physical dosimetry can be performed using experimental means, in this case a standard phantom is irradiated under conditions as close as possible to those of the accident, or using simulation techniques based on Monte Carlo calculations. The Monte Carlo method was applied to several radiological accidents occurred during the last years. As an example, the dosimetric reconstruction performed for an accident due to an Iridium 192 industrial source that occurred in Peru in 1999 is presented. Material and Methods: The technique developed in the laboratory, combining the MORSE Monte Carlo code to a Computer-Assisted Design (CAD) software, can assess the absorbed dose in a numerical anthropomorphic model. The CAD software is used to simulate the accident, taking into account the specific morphology and posture of the irradiated person, as well as the source and the environment characteristics. The circumstances of the accident are as follows. A 37-year-old male welder picked up an Iridium 192 industrial source with an activity equal to 0.96 TBq and placed it in his right back pants pocket during approximately 6 hours. An erythema of the thigh was noticed a few hours after the accident; three months later the surface of the necrotic region was 12 ´ 20 cm2. Results: The skin dose was estimated to be around 400 Gy at the center of the lesion. The calculations performed for various anatomical regions in the vicinity of the source (femur, femoral artery and sciatic nerve) led to doses stretched between 5 and 30 Gy. The mean dose to the total body was estimated to range between 1 to 2 Gy. Conclusion: The MORSE Monte Carlo code, associated to a CAD software, is a powerful tool for dose reconstruction in the case of radiological accident. This method can model various types of accidental situations quickly and realistically.