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A superconducting magnet gantry has been used at HIMAC in NIRS, transporting beams for carbon ion radiotherapy. A second superconducting gantry, with a different design, is under construction in Yamagata University. This invited talk presents an overview of these gantry designs, their advantages for light ion radiotherapy, their operational experiences, and future perspectives for superconducting radiotherapy gantries., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

A superconducting rotating-gantry for carbon radiotherapy was developed. This isocentric rotating gantry can transport carbon ions with the maximum energy of 430 MeV/u to an isocenter with irradiation angles of over ±180 degrees, and is further capable of performing three-dimensional raster-scanning irradiation. The combined-function superconducting magnets were employed for the rotating gantry. The superconducting magnets with optimized beam optics allowed a compact gantry design with a large scan size at the isocenter; the length and the radius of the gantry are approximately 13 and 5.5 m, respectively, which are comparable to those for the existing proton gantries. The total weight of the gantry was estimated to be approximately 300 tons, which is roughly half of the existing gantry for carbon radiotherapy. A construction of the gantry structure begun by 2014, and the installation of the entire gantry system to the Heavy Ion Medical Accelerator in Chiba (HIMAC) complex at National Institute of Radiological Sciences (NIRS) completed by the end of September, 2015. Beam turning begun by October, 2015, and carbon beams, as accelerated by the HIMAC synchrotron, having maximum energy of 430 MeV/u are transported with the rotating gantry to the isocenter. The size and shape of the beam spots at the isocenter were finely tuned over various combinations of the beam energies and the gantry angle. We will present the recent progress as well as the current status of the superconducting rotating-gantry., The 12th European Conference on Accelerators in Applied Research and Technology (ECAART12)

A superconducting rotating-gantry for carbon therapy is being developed. This isocentric rotating gantry can transport carbon ions with the maximum energy of 430 MeV/u to an isocenter with irradiation angles of over 0-360 degrees, and is further capable of performing three-dimensional raster-scanning irradiation. The combined-function superconducting magnets were employed for the rotating gantry. The superconducting magnets with optimized beam optics allowed a compact gantry design with a large scan size at the isocenter; the length and the radius of the gantry are approximately 13 and 5.5 m, respectively, which are comparable to those for the existing proton gantries. Furthermore, the maximum scan size at the isocenter is calculated to be as large as approximately 200 mm square for heavy-ion beams at the maximum energy of 430 MeV/u. A construction and installation of the superconducting gantry is in progress, and beam commissioning will begin from this autumn. We will present a status of the superconducting rotating-gantry., Proceedings of the 13th Heavy Ion Accelerator Technology Conference, HIAT2015, Yokohama, Japan

Gunma University Heavy Ion Medical Center (GHMC) is a compact heavy ion treatment facility* and have experienced 5 years of successful treatment operation. GHMC has 3 treatment room using broad beam (wobbling) irradiation system and 1 experimental irradiation room for the research and development of a spot-scanning irradiation. During the study toward the treatment, several improvements were done in both accelerator and irradiation system. For accelerators, slow extraction from a synchrotron using a transverse rf field is tested**. Compared with conventional extraction system of rf acceleration, ripples of the beam spill (peak to bottom ratio) is reduced from almost 100% to 60%; the deviation of the beam center position and the deviation of the beam size (1σ) are reduced to the order of 0.1 mm. For irradiation system, regularly operation for biological experiments has started form June 2014. In order to shorten the experiment time, 2-dimensional optimization of the irradiation planning was carried out. After the optimization, the irradiation time was reduced by 30% with keeping the dose uniformity within ±2.5%., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A compact injectot for a heavy-ion medical-accelerator complex was developed. It consists f an electron-cyclotron-resonance ion-source (ECRIS)and two linacs, which are a radio-frequency-quadrupole (RFQ) linac and an Interdigital H-mode drift-tube-linac results, as reported earlier. Because the method of alternating-phase-facusing (APF) was used for beam focusing of the IH-DTL, the motion of beam ions would be sensitive to gap-voltage errors, caused during tuning of the gap-voltage distribution and by auto-matic-frequency tuning in actual operation. To study the effects of voltage errors to beam quality, further measurements were performed during acceleration tests. In this report, the effects of voltage errors for the APF IH-DTL are discuseed.

A compact injector, designed for a heavy-ion medical accelerator complex, was constructed. It consists of an Electron-Cyclotron-Resonance Ion-Source (ECRIS) and two linacs, which are a Radio-Frequency-Quadrupole linac and an Interdigital H-mode Drift-Tube-Linac (IH-DTL) having the same operating frequency of 200 MHz. For beam focusing of the IH-DTL, the method of Alternating-Phase-Focusing (APF) was employed. The compact injector can accelerate heavy ions having a charge-to-mass ratio of q/m=1/3 up to 4:0MeV/u. Use of the APF IH-DTL and operating frequency of 200MHz allowed us to design compact linacs; the total length of the two linacs is less than 6m. Beam-acceleration tests of the compact injector system were performed. The measured intensity of accelerated 12C4+ beams with the compact injector was 380 emA. Beam transmission of the APF IH-DTL was estimated to be as high as 96%, which is comparable to the value calculated by a simulation code. Transverse phase-space and energy distributions of accelerated beams were measured and compared with those calculated by the simulation code, and we found that they were agreed well with each other.

A compact Drift-Tube-Linac (DTL) using an Interdigital H-mode (IH) cavity was designed for an injector of medical accelerators. For beam focusing, the method of Alternating-Phase-Focusing (APF) was applied. The APF IH-DTL can accelerate heavy ions having acharge-to-mass ratio of q=m . 1 3 up to 4:0MeV=u. Having optimized an array of synchronous phases for cells, namely arranging drift tubes and gaps appropriately, both longitudinal and transverse focusing strengths were produced just with the rf acceleration field, and therefore no focusing element or cooling equipments had to be installed in the cavity. This allowed us to employ a rather high operating frequency, and hence to design a compact and cost-effective cavity. A further advantage of the APF linac can be found in its operation. Since the parameters to be adjusted are just the level and phase of the input rf, beam tuning can be made with ease. Consequently, the APF linac is suitable for an injector for medical accelerators. Tuning methods of the gap voltages and cavity frequency as well as the design of the cavity for APF IH-DTL have been developed. After constructing the cavity, measurements of the electric field and tuning of the gap voltages were performed. Finally, the rf power was fed into the cavity. In this paper, the design and results of the measurements are described.

A compact injector for medical accelerators was designed. The injector consists of a compact Electron-Cyclotron-Resonance Ion Source (ECRIS) and two linacs, which are a Radio-Frequency-Quadrupole (RFQ) linac and an Interdigital H-mode Drift-Tube-Linac (IH-DTL) having the same operating frequency of 200 MHz. For beam focusing of the IH-DTL, the method of Alternating-Phase-Focusing (APF) was applied. Before constructing the compact injector, a model cavity of the IH-DTL was manufactured, and measurements of the electric-field distributions were performed. The gap-voltage distributions, obtained by integrating the measured electric field, were compared with those calculated using a three-dimensional field solver. The accuracy of the calculated field distributions is discussed. Finally, fine adjustments of the gap voltages using inductive tuners are described.

An isocentric superconducting rotating-gantry for heavy-ion therapy is being designed. This rotating gantry can transport heavy ions having 430 MeV/u to an isocenter with irradiation angles over 0-360 degrees, and is further capable of performing the fast raster-scanning irradiation. For the magnets, combined-function superconducting-magnets were employed. The use of these superconducting magnets allowed us to design a compact gantry, while keeping a large scan size at the isocenter. The superconducting magnets were designed by using a 3D electromagnetic-field solver, the OPERA-3D code. To verify the design of the magnets, beam tracking simulations were performed. Consequently, we found that calculated beam profiles at the isocenter agreed well with those, designed by the beam optics, proving the validity of our design.

Based on more than ten years of experience with HIMAC, we have proposed a new treatment facility for the further development of therapy with HIMAC. The new facility, as an extension of the existing one, has been designed, and the related R&D work has been carried out. The new treatment-facility project was approved at December 2007.