Vol.7 No.4 2015

Research paper : International standardization of four dimensional radiotherapy system (Y. HIRATA et al.)−232−Synthesiology - English edition Vol.7 No.4 (2015) systems with enhanced safety.3 Strategies for the international standardization of 4DRTWe planned to achieve the international standardization of the 4DRT system as a core in the IEC, the representative organization of de jure standards.In order to resolve the general problems of international standardization[11] and the problems of international standardization in the field of radiotherapy equipment,[12] and to smoothly advance the international standardization of 4DRT, we adopted the following strategies.3.1 Selection of committee members from a wide range of fieldsIn addition to the private companies that engage in the production of 4DRT systems, the physicians and medical physicists involved in the clinical practice of 4DRT at universities and research institutes participated as members of the committee to propose the international standard. This allowed discussions of 4DRT from a wide range of fields in Japan.3.2 Ideas to facilitate the formation of international consensusIn contrast to the existing IEC standards that regulate the individual radiotherapy equipment, we proposed the standards for 4DRT systems by combining a number of individual equipment. We focused on the obvious problems that could not be solved by the standards for individual equipment, and we aimed for the international standardization of technologies related to safety for which consensus was relatively easy to obtain from the organizations working on international standards. In addition, we developed a universal phantom (object behaving in the same manner as human tissue with respect to absorption or scattering of the therapeutic rays; this is used to evaluate the performances of radiotherapy systems) that can be used to check the safety of the 4DRT systems. We adopted the policy of creating the safety requirements based on concrete and objective data obtained from the phantom.3.3 International standardization initiated by usersIn the system requirements, we listed the items that were considered clinically important by the users of the 4DRT systems. Then, we advocated the importance of system requirements from a clinical perspective to the experts of the IEC TC62/SC62C WG1 of which most affiliations were private companies.4 Efforts for the international standardizationBased on the strategy explained in chapter 3, we developed the international standardization of 4DRT as follows.4.1 Clarification of the basic conceptIn aiming for the international standardization of 4DRT, we considered the clarification of the basic concept of the international standardization as the most important topic, and discussed this matter in the Japanese national commission. 4DRT directly irradiates the moving tumor, minimizes the damages to the surrounding normal tissues, and reduces the patient’s physical strain. In order to perform safe 4DRT, it is necessary for the equipment that constitute the 4DRT systems to be coordinated and integrated to function smoothly together during the treatment. Mere combinations of existing international standards cannot assure the appropriate and solid coordination of the various equipment necessary to realize the 4DRT systems. Therefore, we decided to propose a set of new safety requirements that are necessary for the appropriate and solid coordination of the 4DRT equipment. However, such basic concept was not set in the initial stages of activity for the international standardization of 4DRT. The basic concepts were developed to clarify the differences between the proposed international standard of 4DRT and the conventional IEC equipment standard in the processes of discussions at the IEC international conferences.4.2 Targets and required accuracy of 4DRT4DRT is a technology that reduces the damages to the surrounding normal tissues in the radiotherapy for tumors that move due to respiratory motion. According to the definitions of the guidelines for respiratory motion management in radiation therapy[13][14] that were developed from a clinical point of view, the respiratory motion management may be applied only when the length of respiratory tumor motion exceeds 10 mm and the expansion of irradiation area required to compensate for the respiratory motion can be reduced to 5 mm or less in all directions, three dimensionally. From these definitions for respiratory motion management, we obtained the quantitative criteria for the length of target tumor motion (greater than 10 mm) and the reduction of the expansion of irradiation area compared with Fig. 4 Organizations involved in the international standardization of 4DRT JEITAJapanese national commissionJIRAJapanese national commissionElectromedical equipmentEquipment for radiotherapy, nuclear medicine and radiation dosimetryDiagnostic imaging equipmentCommon aspects of electrical equipment used in medical practiceIEC TC62(Electrical equipment in medical practice)SC62CSC62BSC62DSC62A


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