Research On Voxel Model Construction And Organ Dose Distribution Of Mouse Used For Radiation Dosimetry

Animal irradiation experiment is vital to study biological effects of radiation. Compared with the average dose, the organ dose of animal can provide more plentiful information and basis for evaluating biological effects and dose-effect relation research. The animal organ dose is difficult to be measured directly by physical methods. In recent years, with the development of tomograph imaging technologies, the organ dose calculation methods based on the voxel model and Monte Carlo technique have been increasingly maturing and have been used for human dosimetry in radiation protection. However, the organ dose calculations aiming at evaluation of biologicial effects are being on the beginning stage, which lacks voxel models and organ dose data.In this paper, a voxel model of mouse was constructed, a set of mouse organ dose conversion coefficients for external photon and neutron irradiation were obtainded by using Monte Carlo method, and the mouse organ dose distribution also was analyzed and concluded. The main results and conclusions are as follows:1. At first, a series of image processes including registration, identification and segmentation were carried out for a total of 418 color images of successive cryosections of a normal male mouse, 28g in weight by using Matlab 7.0 and Photoshop 8.0 software.Then 3D reconstruction of the mouse model was achieved through programming with Visual C++ and Visualization Toolkit (VTK). After these, a mouse voxel model comprised by total number of 9,424,000 voxels, each of which is size of 0.2mm×0.2mm×0.2mm, was constructed. The model contained 14 key organs or tissues including skin, bone, eye, brain, heart, lungs, liver, kidneys, adrenal glands, stomach, spleen, pancreas, bladder, testis and muscle.2. The location and physical property of each voxel in the mouse model were confirmed through coupled programming with Matlab 7.0 and Monte Carlo code MCNP. The input file of the mouse voxel model used in MCNP was achieved to perform particle transport simulation by combining the mouse voxel model and Monte Carlo method.3. As for the Monte Carlo code MCNP, the organ dose calculation methods of voxel model used for external photon and neutron irradiation were thoroughly investigated and the selection rules of physical models and tally types for different energy of photon and neutron were also concluded,which provide basis of methodology for acquiring correct mouse organ dose . 4. Monte Carlo simulation with MCNP was carried out to obtain mouse organ dose conversion coefficients for 22 external monoenergetic photon beams (0.01MeV ~10 MeV) and 37 external monoenergetic neutron beams(10-9MeV~20MeV) under five different irradiation geometry conditions (left lateral, right lateral, dorsal-ventral, ventral-dorsal, and isotropic). The results and uncertainty were given in form of table. The set of organ dose conversion coefficients are basic data of mouse dosimetry and can be used to acquire organ dose when irradiation conditions have been known.5. The paper have discussed the organ dose difference affected by a series of factors including irradiation geometry conditions, particle energy, location, shape and size of organ, the individual difference. The results show that the organ dose difference can reach almostly 50%～60% for photon irradiation and 100%～120% for neutron irradiation.6. A platform for theoretical study of mouse dosimetry was constructed, which can be used to simulate and calculate the mouse dosimetry data for photon, neutron and other particles (such as electron and proton) irradiation under internal and external irradiation conditions.