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Takahashi, Fumiaki; Sato, Kaoru; Endo, Akira; Ono, Koji*; Ban, Nobuhiko*; Hasegawa, Takayuki*; Katsunuma, Yasushi*; Yoshitake, Takayasu*; Kai, Michiaki*
Health Physics, 109(2), p.104 - 112, 2015/08
Times Cited Count：8 Percentile：56.13(Environmental Sciences)A dosimetry system, named WAZA-ARI, is developed to assess accurately radiation doses to persons from Computed Tomography (CT) examination patients in Japan. Organ doses were prepared to application to dose calculations in WAZA-ARI by numerical analyses using average adult Japanese human models with the Particle and Heavy Ion Transport code System (PHITS). Experimental studies clarified the radiation configuration on the table for some multi-detector row CT (MDCT) devices. Then, a source model in PHITS could specifically take into account for emissions of X-ray in each MDCT device based on the experiment results. Numerical analyses with PHITS revealed a concordance of organ doses with human body size. The organ doses by the JM phantoms were compared with data obtained using previously developed systems. In addition, the dose calculation in WAZA-ARI were verified with previously reported results by realistic NUBAS phantoms and radiation dose measurement using a physical Japanese model. The results implied that analyses using the Japanese phantoms and PHITS including source models can appropriately give organ dose data with consideration of the MDCT device and physiques of typical Japanese adults.
Takahashi, Fumiaki; Sato, Kaoru; Endo, Akira; Ono, Koji*; Yoshitake, Takayasu*; Hasegawa, Takayuki*; Katsunuma, Yasushi*; Ban, Nobuhiko*; Kai, Michiaki*
Progress in Nuclear Science and Technology (Internet), 2, p.153 - 159, 2011/10
Computed Tomography (CT) is one of the most useful tools for medical diagnosis, and is becoming a major source of medical exposure in developed countries. Appropriate radiation protection in CT examinations is emphasized by international organizations, such as the International Atomic Energy Agency (IAEA), because the patients receive higher radiation doses than in conventional radiography. Medical staffs can acquire dose information on the conditions of some CT examinations with available dosimetry systems, which had been already developed. These systems utilize datasets of organ and tissue doses, which were derived with Monte Carlo calculations. Methods in computational analyses, however, have been improved, since these calculations had been performed. Then, our new dosimetry system for CT examination, WAZA-ARI, is being developed to estimate radiation dose based upon the state-of-art numerical analyses. Our analysis adopts Particle and Heavy Ion Transport code System (PHITS) coupled with a voxel-type phantom, JM phantom, for the organ dose calculation. PHITS has advantageous to define the model of photon emission from X-ray tube in a CT device for radiation transport calculations. The physique and mass of organs for JM phantom are similar to those for average Japanese male adults. Since the goal of WAZA-ARI is to provide dosimetric information of arbitrary patient, it is important to evaluate uncertainty due to different configurations in human bodies between JM phantom and individual patients. For this purpose, the organ doses are calculated and compared for different human models; another Japanese male adult voxel phantom and the ICRP reference voxel phantom, which is constructed on the basis of Caucasian data.
Ban, Nobuhiko*; Takahashi, Fumiaki; Sato, Kaoru; Endo, Akira; Ono, Koji*; Hasegawa, Takayuki*; Yoshitake, Takayasu*; Katsunuma, Yasushi*; Kai, Michiaki*
Radiation Protection Dosimetry, 147(1-2), p.333 - 337, 2011/09
Times Cited Count：27 Percentile：87.94(Environmental Sciences)A web-system of WAZA-ARI is being developed to assess radiation dose to a patient in a Computed Tomography (CT) examination. The databases of organ doses for WAZA-ARI were derived by the Japanese adult Male phantom (JM phantom) combined with the Particle and Heavy Ion Transport code System, PHITS. In the Monte Carlo simulation, the phantoms were irradiated with a 5 mm-thick fan-shaped photon beam, which was moved every 5 mm along the body axis from the upper leg to the top of head. The attenuation by the beam-shaping filter (bow-tie filter) was also taken into account here. The MIRD-type phantom was also applied to the calculations. The MIRD phantom sometimes showed step changes for organ doses, while smoother curves were obtained for JM phantom. The dose data by JM phantom were incorporated into the WAZA-ARI system, which has been implemented on a Linux server. With regard to the system implementation, the system has achieved a high degree of flexibility without commercial software.
Takahashi, Fumiaki; Sato, Kaoru; Endo, Akira; Ono, Koji*; Yoshitake, Takayasu*; Hasegawa, Takayuki*; Katsunuma, Yasushi*; Ban, Nobuhiko*; Kai, Michiaki*
Radiation Protection Dosimetry, 146(1-3), p.241 - 243, 2011/07
Times Cited Count：20 Percentile：81.61(Environmental Sciences)A web-system of WAZA-ARI is being developed to assess radiation dose to a patient in a Computed Tomography (CT) examination. WAZA-ARI utilizes a set of organ and tissue doses in a database for the dose assessment, according to the given resources with a consideration of the examination condition. The organ and tissue doses in the database have been derived with the Particle and Heavy Ion Transport code System, PHITS. Modeling of the patient was a significant issue in the radiation transport calculation. JM phantom, whose height (171 cm) and weight (65 kg) are near to those averaged over Japanese male adults, was incorporated to PHITS as a human model. Since JM phantom consisted of about 1 mm
size voxel, the shapes could be realistically reproduced even for small organs such as thyroid, adrenals. Masses of most organs could be also adjusted to the averaged values of Japanese male adults. In addition, our calculations introduced a new phantom without arms based upon JM phantom, because the patient usually puts arms toward the head direction in a torso examination. Some of organ doses calculated by JM phantom were compared with results, which were derived with a MIRD-type phantom. Differences could be seen in some organ doses between the phantoms, if photon attenuations in a shaping (Bow-tie) filter were taken into account to a source model in PHITS.
Ban, Nobuhiko*; Takahashi, Fumiaki; Ono, Koji*; Hasegawa, Takayuki*; Yoshitake, Takayasu*; Katsunuma, Yasushi*; Sato, Kaoru; Endo, Akira; Kai, Michiaki*
Radiation Protection Dosimetry, 146(1-3), p.244 - 247, 2011/07
Times Cited Count：20 Percentile：81.61(Environmental Sciences)We are developing a web-based system, WAZA-ARI, for the dose calculation of patients undergoing X-ray CT examinations. Tissue doses were calculated in a Japanese adult male phantom (JM phantom) using a Monte Carlo code, PHITS, and the normalized dose coefficient data are stored as XML files. The system is implemented in Java on a Linux server running Apache Tomcat, which is accessed via a web browser over a network. Users are requested to choose scanning options and to input parameters in the data entry screen. The corresponding dose data are called upon input, and they are summed over the scan range specified by the user to estimate unit tissue doses. Tissue doses are computed based on the radiographic exposure (mAs), the beam pitch and air kerma at the beam center on the axis of rotation. Users can also use their own air kerma, CTDI vol and DLP values for the dose computation instead of the default setting. Although the dose coefficients are prepared for only limited CT scanner models currently, our system has achieved high usability and easy maintenance without commercial software. Possibility of further expansion for the practical application is also discussed.
