Presentation Design and performance of daily QA system for carbon ion therapy at NIRS

早乙女, 直也  ,  古川, 卓司  ,  水島, 康太  ,  原, 洋介  ,  丹正, 亮平  ,  皿谷, 有一

Since carbon ion deposits most of their energy in the last final millimeters of their trajectory, the accuracy of the beam energy/range is required for carbon ion treatment especially for using scanning method. Physical advantages of carbon ion are not only for the beam direction, but also for the lateral direction compare with conventional photon or proton beam. Although QA procedures are necessary for establishing safe and accurate dose delivery of any radiation therapy treatment modality, much high level of QA procedures are required for carbon-ion therapy. At the National Institute of Radiological Sciences (NIRS), we have been commissioning the rotating-gantry system for the carbon-ion radiotherapy. This rotating-gantry can transport heavy ions having 430 MeV/u to an isocenter with irradiation angles of over ±180° that is able to rotate around the patient so that the tumor can be irradiated from many directions. A three-dimensional pencil beam scanning irradiation system which is equipped with the rotating-gantry, provide the optimal use of physical characteristics of carbon-ion and to achieve accurate treatment. This irradiation system can provide the treatment of a moving target by fast scanning irradiation. A maximum scanning velocity is 100 mm/ms at isocenter. To ensure the treatment quality using such a complex system, calibration of the primary dose monitor, range check, dose rate check, machine safety check, and some mechanical tests should be performed efficiently. For this purpose, we have developed a measurement system dedicated for quality assurance (QA) of this gantry system. The system consists of an ionization chamber system and a scintillator system. For the ionization chamber system, a Farmer type ionization chamber is inserted into the center of a plastic water phantom. The thickness of the phantom could be changed so that employ both calibration of the output at entrance and output checking at center of the irradiation field. For the scintillator system, the ranges of beams are verified using a CCD camera and a scintillator. From the taken images, maximum gradient points are determined by some image processing and compared with reference data. In this paper, we describe consideration of the daily QA system for the rotating-gantry.
The 12th European Conference on Accelerators in Applied Research and Technology (ECAART12)参加・発表

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