Operation of scanning irradiation system at nirs-himac

Three-dimensional scanning irradiation system has been utilized for treatment since 2011 at Heavy Ion Medical Accelerator in Chiba (HIMAC), in the National Institute of Radiological Sciences (NIRS). The scanning irradiation requires strict checking for beam position, size, range, and spill shape, because any changes in the scanned beam will cause a significant impact on the irradiation dose. Therefore, the operators perform the regular quality assurance (QA) checks for the therapeutic beam according to daily, monthly and halfyearly reviews. Daily QA: Before starting patient treatment, the reproducibility of the beam should be checked. Therefore, daily QA procedures require not only adequate but also simple to not skilled operator. Monthly QA: It is important to periodically acquire a reference data for daily QA checks. Once a month, we perform additional beam QA to measure the characterization of beam in detail. Half-yearly QA: After the scheduled half-yearly shut down of HIMAC, we check the condition of the scanning system in detail. Additionally, we newly measure the characterization of beam to determine a reference for daily QA and monthly QA and re-tune the current of magnets from the measured results. In this paper, we report periodic QA as an operation of scanning irradiation system at NIRS-HIMAC. Improvement in daily QA procedures and relevant progress are described.