The researches of medical and environmental radiation protection dose 医学と環境における放射線防護線量に関する研究

Nowadays, with the development of modern radiation science, application of radiation exposure has been paid more and more attention in various fields. Although there are many benefits for human by the use of radiation in such as medical diagnose and treatment, utilization of nuclear power, more efforts should be made to radiation hazards and their control that are often neglected. The researches in this study were intended to meet the requirements with the center of radiation protection dose in a wide range which attracts the most attention and are involved, either directly or indirectly, with ionizing radiation, including diagnostic exposure doses in paediatric CT, radiation doses in normal tissues which surrounding the targets in radiotherapy, and environmental exposure doses in Fukushima nuclear accidental areas. In the researches about paediatric CT, the reference radiation dose and organ doses from chest CT studies of children were estimated by using the data of clinical practice of the National Center for Child Health and Development in Japan. In composing local diagnostic reference doses and organ doses, the aim of this research was to provide a reliable and accurate data on the exposures in X-ray CT examinations for paediatric patients, which could be useful for optimization of radiation protection. Moreover, to evaluate the changes of organ doses depending on the thickness of the soft tissue on body surface in paediatric abdomen CT, radiation doses were measured with radiophotoluminescence glass dosemeters set in various organ positions within a 6-year-old child anthropomorphic phantom with slices of soft tissue equivalent materials attached on the surface, and organ doses were evaluated from the measurement values. In the researches of radiation treatment, the characteristics of the hepatic tumor movement caused by respiration were evaluated by using fluoroscopy. To decrease exposure doses in healthy organs that surrounding targets in tumor tracking treatment, the feasibility of prospective tracking of respiratory caused tumor motion signal based on autoregressive model was also tested to compensate the retardation time that often exists between the acquisition of motion signal and the action execution. In the researches of environmental radiation exposure in Fukushima nuclear accidental areas, radiocesium contaminated soil was obtained from a polluted area in Fukushima and was remedied under strict control by use of electrokinetics, and to accurately measure surface radiation doses after depollution operations, a shield for environmental radiation dose survey meters in badly contaminated areas has been developed. According to the results of the researches, a set of CTDIs and organ doses in paediatric chest CT scan was compiled for the National Center for Child Health and Development based on children's weights. Organ doses in paediatric abdomen CT were evaluated under different thicknesses of soft tissue on the surface of the same child anthropomorphic phantom. In the radiation therapy, thoracic and abdominal tumor motion has been verified to be pace with respiratory movement, and Burg's method has been proved to be effective to predict tumor motion in real-time, and moreover, it could make a contribution to protection for normal organs. Radiocesium contaminated soil was laboratory depolluted effectively by use of electrokinetic remediation technology, and a new shield for survey meters was successfully developed to precisely measure the environmental radiation dose and evaluate decontamination work in the Fukushima.

首都大学東京, 2013-09-30, 博士（放射線学）, 甲第452号