Development of scanning irradiation in Gunma University Heavy Ion Medical Center

Spot scanning irradiation system of carbon ion beam has been developed in Gunma University Heavy Ion Medical Center. During 2013, the beam size and position was stabilized with the use of a pattern-excited steering magnet and optimization of the optic parameters. After these improvement, 3-dimensional spherical field uniform irradiation was carried out based on the measurement of pencil beam profile and depth-dose distribution. The irradiated dose distribution agreed with the calculation within 3%. An experiment of rotating energy absorber has been carried out to suppress the range variation in the extraction period. In order to improve the dose linearity and reproducibility in the low dose region less than 1Gy, the response of I/V converter circuit was improved from 3kHz to 50kHz. After these improvement, the uniform box irradiation was utilized routinely for the animal (mice) experiment from April 2014. (author)