The Internal Radiation Dosimetry Research Based On The Visible Chinese Human Voxel Data

Medical radiation is the main source of ionizing radiation exposured to human, and it accounts for about 98% in all of the factors in man-made radiations. Internal radiation therapy, such as the radionuclide imaging and radioactive seed implantation in brachytherapy for tumor, are preferred by doctors and patients because of its minimally invasive, less complications and good effect. The internal radiation therapy can cure disease but it also delivers ionizing radiation risk to human. In clinic, we always look forward to ensuring the quality of treatment while minimizing radiation to patient and surrounding environment. Therefore, the internal radiation dose calculation to human is important and significant in the field of radiation protection and clinic radiology.In this work, based on the high resolution Visible Chinese Human (VCH), we developed the voxel model by segmenting and labeling the original images. In combination with the Monte Carlo method, the transport procedure of photon and electron was simulated, and the internal radiation dose common database based on Chinese human was established. The internal radiation dose for Intravascular Brachytherapy (IVBT), prostate brachytherapy and radionuclide inhalation were deeply investigated with different radionuclides based on this database. The detailed topics and results are as follows:(1) The transport procedure of photon and electron in 29 organs and tissues of the model were simulated. The internal dose conversion factors were obtained, and the radiation dose common database based on Chinese human was established. In comparison with other studies, discrepancies were found to be correlated with the racial and anatomical differences in organ mass and inter-organ distance. Electron was found not only has radiation to source organs but also to surrounding organs. The target organs were classified according to the radiation doses.(2) In IVBT research, the coronary artery was finely segmented and reconstructed from the vascular system. The internal radiation doses for organs were calculated with source in different locations of the coronary artery. The discrepancies in organ doses for the three radionuclides 192Ir, 188Re and 32P were compared. Potential risk to human was also estimated. The results obtained in this work suggested that the doses to target organs were sensitive to source location, 188Re and 32P had higher dose in source organ and lower dose in target organs in comparison with those of 192Ir. Moreover, the high dose rate 192Ir was proved to be dangerous to human in IVBT.(3) In prostate branchtherapy, the mean absorbd doses and dose distributions for organs were obtained from three commonly used radionuclides 125I, 103Pd and 192Ir. The results suggested that the dose distributions in organ were mainly related to the size, shape and location of the organ. Organs with uniform shapes and far distances from the source may have uniformed dose distributions. The committed exposure doses to family members were 0.576 mSv from 125I and 0.506 mSv from 103Pd. The annual exposure doses to doctors were 0.183 mSv for hands and 0.046 mSv for whole body from 192Ir. All of the doses were below to the limit of 1 mSv.(4) The internal radiation doses were investigated when people temporal or perennial inhaled the 131I of 1.85×104 Bq/m3 without the consideration of gas exchange and metabolism. The environmental safety limit concentration was also investigated. The results suggested that the internal dose was 0.031 mSv and 0.977mSv for temporal and perennial inhalation respectively. The environmental safety limit concentration of 131I was 1.89×104 Bq/m3. The highest annual effective dose caused by 131I in the air of all provinces in China currently was 5.28×10-5μSv, which was much smaller than the dose limit of 1mSv, and there was no internal radiation harm to human.In this study, the internal dosimetry data based on other models that were used to apply to Chinese adult population are complemented with Chinese specific data, which can provide more accurate doses for Chinese human internal radiation research. The radiation dose obtained from the IVBT, protate branchtherapy and radionuclide inhalation may contribute to the existing data, provide precise control in prescription time and dose, evaluate the safety of therapy and assess the risk to human from radionuclide inhalation.