Research On The Multiscale Dosimetry Of Radon Progeny And Its Application

As radon is one of the most important natural radiation sources,its radiation hazard has always been a hot research topic in radiation protection field.There are two approaches to study on the health effects induced by radon radiation: epidemiological investigation and radiobiological experiment.Efficacy of both methods highly depends on the accuracy of dosimetry parameters.Therefore,it is essential to develop a more detailed dosimetry model for radon progeny hazard evaluation.By following the physical mechanism of radon radiation,this study investigated all involved processes: radon progeny particles are inhaled in the lung,deposit and absorbed in theair pathway,simultaneously decay and transferred to other organs or tissues,and the alpha particles they emitted may hit and deposit energy in the sensitive cells within the respiratory tract.The consequent health effects were also discussed.In summary,this thesis focused on the following issues:1.Developed an ultra-high resolution,full lung respiratory tract model.In this thesis,a mathematical model for human respiratory tract was first established using anatomic bronchial parameters.Then it was voxelized to build a numerical voxel model,and integrated into the Chinese reference adult male voxel model.This proposed model is the very first respiratory voxel model in the world featured by consecutive 16-generation bronchial structures.The model is the fundamental tool for the dose calculation in this thesis.And the model construction method proposed also provides the possibility for individual dose calculation in the future.2.Biodynamic research for radon progeny particles distribution.The initial deposition fraction in various region of respiratory tract model was calculated using deposition model.And migration of radon progeny after absorbed into blood or transferred to other organs/tissues was obtained through a clearance model.Furthermore,fluid dynamic software was used to simulate the transportation of radon progeny particles in the bronchial region.The deposition distribution was obtained for the position information of source particles in dose calculation.3.Dose calculation.Using the respiratory tract model and source particle distribution data,absorbed fraction for alpha particles and effective dose conversion factor for radon progeny were calculated.In the meanwhile,dose distribution within the respiratory tract was obtained by scoring deposited energy for each voxel.Radiation sensitive cells were modeled within the maximum dose voxel and the maximum cell dose was calculated.4.Application of dose results.Dose distribution data could be used for the further research of radiation damage and cancer risk.Two typical application were discussed in this thesis.On one hand,risk for lung cancer induced by radon was assessed under typical room radon level.Under some conditions,the relationship between the dose distribution and cancer incidence was analyzed.On the other hand,the calculation method established in this study was applied in abnormally high radon areas.Results show that,the maximum absorbed dose of sensitive cells in bronchi could reach or exceed the threshold dose that may lead to cell death,in some extreme cases.