BEAM QUALITY ENSURING INSTRUMENTS AT THE GUNMA UNIVERSITY HEAVY-ION MEDICAL CENTER

Since carbon beam based cancer therapy started at the Gunma University Heavy-ion Medical Center in the year 2010, the total number of treated patients increased to 306 by the end of 2011. This fiscal year, already 164 patients have been treated. In order to control the medical beam qualities, i.e., position, size and intensity of the beam, monitoring devices were mounted on the high-energy beam transport line. The beam position and size can be measured and tuned with a screen monitor, which consists of a fluorescent screen and a CCD camera. Just before starting the treatment, the operators check for a proper beam position by strip-line monitor measurements placed close to the isocenter. The irradiation dose is controlled using two secondary electron emission monitors placed before wobbling magnets. This dose monitor is helpful as for high beam intensities it’s less affected by the recombination effect. The technical layout of all beam monitors are described.