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Research paper−229−Synthesiology - English edition Vol.7 No.4 pp.229-238 (Mar. 2015) Society for Radiation Oncology (JASTRO) in 2010[2] and the estimated Japanese population-based cancer registration by the Center for Cancer Control and Information Services, National Cancer Center.[3] In the 1990s, the radiation therapy that used high-energy x-rays produced by small medical linear accelerators (LINAC) became widespread, and the number of its application increased, and this number is expected to grow. The rise in the death rate due to cancer is a trend seen in many aging countries, and there is a growing international need for radiation therapy. 1.2 Four-dimensional radiotherapy (4DRT)In principal radiation therapies, x-rays, electrons, protons, and carbon are used as therapeutic rays. In any radiation therapy, the main issue is to irradiate the necessary quantity of therapeutic rays to the tumor that may move due to respiration or other factors and to minimize the damages to the surrounding normal tissues. To solve this problem, the R&D of 4DRT started around 2000 to enhance the timing accuracy of irradiation in addition to spatial accuracy.[4]The 4DRT was employed around the world, and 4DRT was defined as “a therapy that explicitly includes the temporal 1 Introduction1.1 Importance of radiation therapyAccording to the annual estimated vital statistics of the Ministry of Health, Labour and Welfare for 2010,[1] cancer was the most common cause of death for the Japanese, and about 25 % of all patients were treated with radiation therapy. The radiation therapy is a medical treatment that utilizes the difference of radiation sensitivity between the tumor cells and normal cells, and destroys only the tumor cells without damaging the normal cells by controlling the quantity of therapeutic rays. The characteristic of radiation therapy is that it does not require surgery, can preserve the form and functions of the affected area, and has relatively short treatment time. Therefore, it is suitable for treatments of elderly people. In addition, it has the advantage that, in principle, it is capable of treating cancers in any region of the patient’s body.Figure 1 shows the trends of the number of individuals affected with cancer and the number of patients who are treated with radiation therapy. This figure was created based on the results of the structural survey by the Japanese - Enhancement of effects of irradiation and assurance of safety-In radiation therapy for cancer, there are possibilities of position changes of the affected area during irradiation due to respiration of a patient. In order to enhance effects of irradiation for the affected area and minimize damages to the surrounding normal tissues, four dimensional radiotherapy (4DRT), which can take into account time variation of the three-dimensional position of the affected area, has been recently developed, and has been achieving significant therapeutic effects. We have proposed the International Electrotechnical Commission (IEC) standards including technical requirements of the safety aspects of the systems which realize this 4DRT, taking into account the time aspect. The reason for the proposal is that international standardization will be very effective to ensure safety of 4DRT, and international standards of IEC will have compelling force if regulatory agencies refer to them. The purpose of this paper is to summarize the analysis of the strategy in a precedent endeavor toward international standardization of the 4DRT systems, for which demands are increasing. The main point of the strategy is forming an international consensus by bringing together the opinions of specialists from various fields from a clinical point of view, focusing on the international standardization of the technical requirements of the safety aspects of the 4DRT. Based on such a strategy, we will promote developing new standards by evaluating the overall safety of the 4DRT systems for further expanding use, in addition to updating existing standards of particular equipment which constitute the 4DRT systems.International standardization of four dimensional radiotherapy systemKeywords : Four dimensional radiotherapy, real-time tumor-tracking radiotherapy, dynamic tracking, international standardization, IEC[Translation from Synthesiology, Vol.7, No.4, p.238-246 (2014)]Yuichi Hirata1*, Naoki Miyamoto1, Morihito Shimizu2, Mitsuhiro Yoshida3, Kazuo Hiramoto4, Yoshiaki Ichikawa5, Shuji Kaneko6, Tsuyoshi Sasagawa7, Masahiro Hiraoka8 and Hiroki Shirato11. Hokkaido University Graduate School of Medicine North-15 West-7, Kita-ku, Sapporo 060-8638, Japan *E-mail: , 2. National Metrology Institute of Japan, AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568, Japan, 3. MITSUBISHI HEAVY INDUSTRIES, LTD. 4-6-22 Kan-on-shin-machi, Nishi-ku, Hiroshima 733-8553, Japan, 4. Hitachi, Ltd. 7-2-1 Omika-cho, Hitachi-shi 319-1221, Japan, 5. Hitachi, Ltd. Marunouchi Center Building, 1-6-1 Marunouchi, Chiyoda-ku 100-8220, Japan, 6. Kyoto University Hospital 54 Kawaharacho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan, 7. SHIMADZU CORPORATION 1 Nishinokyo-Kuwabaracho, Nakagyo-ku, Kyoto 604-8511, 8. Kyoto University Graduate School of Medicine Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan Original manuscript received January 31, 2014, Revisions received June 20, 2014, Accepted June 23, 2014

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