Research On Radiation Dosimetry Of Different Postures Based On Boundary Representation Phantoms

It's necessary to establish the anthropomorphic computational phantom for calculating the radiation dose of human body.The BREP(Boundary Representation)phantom can reflect the human anatomical features and be adjusted flexibly.It has many advantages comparing with mathematical phantom and voxel phantom.And it has been used in the area of radiation dosimetry gradually.The BREP phantom was combined with the Monte Carlo codes for studying the radiation dose in this paper.And the organ absorbed dose conversion coefficient and effective dose conversion coefficient of the photon were calculated under six irradiation geometries.As most of the radiant exposure involve realistic human postures is not standing posture.So it is significant to study the dosimetry dose of the phantom of various postures.Based on Chinese reference adult phantom and the BREP modelling method,the Chinese reference female BREP phantoms of different postures were established which was changing the standing phantom into sitting,walking,squatting postures using the Rhinoceros software.Then the location and quality of the organs and tissues were adjusted.After adjustment,the quality of organs and tissues of the phantoms were within ?5% compared with the quality of Chinese reference female.As the BREP phantom could not be imported into Monte Carlo software directly.So the BREP phantoms of three postures were transformed into polygon mesh phantoms.Then every organs and tissues were voxelized using BINVOX software individually.The voxel matrix was handled by MATLAB software.Each organ and tissue was given a specific number.Finally the whole voxel matrix was combined containing all organs and tissues.The voxel resolution of the phantom of sitting,walking and squatting postures are0.64cm?0.64cm?0.64 cm,0.67cm?0.67cm?0.67 cm,0.58cm?0.58cm?0.58 cm,respectively.Using the Chinese reference female BREP phantom of different postures and MCNP code,the organ absorb dose conversion coefficient and effective dose conversion coefficient of 20 photon monoenergetic beams from 0.01 MeV to 10 MeV were carried out under six standard irradiation geometries,AP,PA,LLAT,RLAT,ROT,ISO.The dose conversion coefficient of different radiation geometries,different postures and different organs were compared with each other and analyzed.The results indicate that the variation trends of organ absorb does and effective dose conversion coefficients of the BREP phantom of differentpostures are similar under same irradiation geometry.But the postures,location of the organ and irradiation geometries will have an impact on the dose.The differences of dose conversion coefficient of these phantoms are less than 20% under most photon energy points.When the photon energy was under 0.1MeV,the differences of the dose conversion coefficients are obvious.