Research On Radiation Properties Of Tissue-equivalent Materials In Chengdu Dosimetric Phantoms (CDP)

With more attention paid to the radiation hazard, anthropomorphic phantoms, as the substitute for the real body, were used in the fields of radiation protection, diagnosis, therapy, teaching and the research on the radiation standard more and more extensively. Being the fundamental element of the anthropomorphic phantoms, the research on the radiation properties of tissue-equivalent materials became a hotspot in the eyes of medical physicist. Early in the beginning of last century, some natural materials were used to manufacture radiation tissue-equivalent materials, the purpose of which was to evaluate the radiation dose roughly, as the substitute for human body. In the middle of the last century, man-made polymer materials began to be the raw materials of the radiation tissue-equivalent materials. The research on the anthropomorphic phantoms and radiation tissue-equivalent materials of our country started in the early 1980s. Professor LIN Da-quan of Sichuan University researched and produced the Chinese first male anthropomorphic phantom, the Chinese first female pelvic phantom, the Chinese first female breast phantom and the Chinese first intensive treatment phantom successfully. In 1992, this series of anthropomorphic phantoms were named Chengdu Dosimetric Phantoms (CDP) in ICRU Report 48 by International Commission on Radiation Units and Measurements. To improve the properties of the tissue-equivalent materials further, it was essential to research the method of design, the synthesis technology, the equivalent properties and the stability of the materials systematically. Using the reference of the theory that the element content of human body could be calculated on the base of CT number, a method used to design the radiation tissue-equivalent materials based on the CT number was brought up. From the basic concept of CT number, the relationship equation between the CT number and the content of radiation tissue-equivalent materials which interplayed with X orγray was derived. Two important constants were ascertained by least squares. The designed formula for common radiation tissue-equivalent materials was given, including soft tissue radiation equivalent material, bone radiation tissue-equivalent material, brain radiation tissue-equivalent material and lung radiation tissue-equivalent material.According to the theory of the bionic template polymerization process, the technics route to manufacture the radiation tissue-equivalent materials in Chengdu Dosimetric Phantoms was provided. This technics route to manufacture radiation tissue-equivalent materials could be finished in the normal temperature and atmospheric pressure. It was good for saving the cost of the reaction equipments, meanwhile the uniformity of the radiation tissue-equivalent materials would be better. In this process, the products would not become coking, and the experiments were easy to repeat, at the same time the properties of the materials produced in this process werestable.On the base of the analysis of the basic element contents and densities of the irradiation tissue-equivalent materials in Chengdu Dosimetric Phantoms, such as soft tissue radiation equivalent material, bone radiation tissue-equivalent material, brain radiation tissue-equivalent material and lung radiation tissue-equivalent material, the radiation properties of this four materials were evaluated from mass attenuation coefficient, effective atomic number, liner attenuation coefficient and electron density. The results demonstrated that the main radiation tissue-equivalent materials in Chengdu Dosimetric Phantom owned a broad energy scope and good radiation equivalence. So it reached the A grade of the international recommended standards. As a result, these materials could be used to demarcate the various irradiation diagnostic and therapy facilities and radiation protection facilities. On the other hand, the stability tests were done to determine the stability of radiation tissue-equivalent materials in Chengdu Dosimetric Phantoms, taking muscle radiation tissue-equivalent material as an example. And the effective life of the materials was estimated.The methods to design radiation tissue-equivalent materials and to evaluate the equivalence of the materials given in this paper provided the theory value and practical significance to enhance the equivalence of radiation tissue-equivalent materials in Chengdu Dosimetric Phantoms. The theoretical basis was also supplied for the mass produce of the equivalent materials.