Development of Qa System for the Rotating Gantry for Carbon Ion Therapy at Nirs

At the National Institute of Radiological Sciences (NIRS), we have been developing the rotating-gantry system for the carbon-ion radiotherapy. This system is equipped with a three-dimensional pencil beam scanning irradiation system. To ensure the treatment quality, 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 ion beam’s dose output are calibrated by measurement using an ionization chamber. A Farmer type ionization chamber is inserted into the center of a water equivalent 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. The ranges of beams are verified using a scintillator and a CCD camera system. 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 for the rotating-gantry.