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A study of multiple-ion therapy with charged heavy-ion beams was performed to improve outcomes of refractory cancer treatments. We proposed the accelerator operation method for applying the multiple-ion therapy, to quickly switch the ion species and energies of the output beams. In this method, the irradiation ion species can be changed only by switching the selected ion source and the injector parameters, and the output beam energies can be varied without changing the magnetic operation patterns of the synchrotron. We verified the effectiveness of our approach by conducting experiments at the Heavy Ion Medical Accelerator in Chiba (HIMAC) and confirmed that the approach can provide the fast switching of both the ion species and the beam energies. The experimental results also demonstrated that our approach will greatly reduce the commissioning time and the routine adjustments for multiple-ion beams. [ABSTRACT FROM AUTHOR]

Multiple-energy synchrotron operation was developed to realize fast 3D scanning irradiation for carbon-ion radiotherapy. This type of operation can output various carbon-ion beams with different energies in a single synchrotron cycle. The beam control system used in this kind of operation was developed to quickly provide the beam energy and intensity required from the irradiation control system. The performance of the system was verified by experimental tests. The system could output beams of 197 different energies in 63 s. The beam intensity could be controlled for all the output beams without large ripples or overshooting. The experimental test of irradiation for prostate cancer treatment was also successfully performed, and the test results proved that our system can greatly reduce the irradiation time. [ABSTRACT FROM AUTHOR]

Abstract: Multiple-energy synchrotron operation providing carbon-ion beams with various energies has been used for scanned particle therapy at NIRS. An energy range from 430 to 56MeV/u and about 200 steps within this range are required to vary the Bragg peak position for effective treatment. The treatment also demands the slow extraction of beam with highly reliable properties, such as spill, position and size, for all energies. We propose an approach to generating multiple-energy operation meeting these requirements within a short time. In this approach, the device settings at most energy steps are determined without manual adjustments by using systematic parameter tuning depending on the beam energy. Experimental verification was carried out at the HIMAC synchrotron, and its results proved that this approach can greatly reduce the adjustment period. [Copyright &y& Elsevier]

Abstract: A raster scanning method has been developed for cancer therapy at NIRS–HIMAC. This method requires a high-accuracy beam current control and fast beam-on/off switching. We have developed a feedback control system of the beam current with the RF-knockout slow extraction method. The system has allowed a stable response to beam-on/off switching using a feedback control delay function with a beam-current ripple of 7%. [Copyright &y& Elsevier]

Since 2011, a three-dimensional (3D) scanning irradiation system has been utilized for treatments at the National Institute of Radiological Sciences-Heavy Ion Medical Accelerator in Chiba (NIRS-HIMAC). In 2012, a hybrid depth scanning method was introduced for the depth direction, in which 11 discrete beam energies are used in conjunction with the range shifter. To suppress beam spread due to multiple scattering and nuclear reactions, we then developed a full energy scanning method. Accelerator tuning and beam commissioning tests prior to a treatment with this method are time-consuming, however. We therefore devised a new approach to obtain the pencil beam dataset, including consideration of the contribution of large-angle scattered (LAS) particles, which reduces the time spent on beam data preparation. The accuracy of 3D dose delivery using this new approach was verified by measuring the dose distributions for different target volumes. Results confirmed that the measured dose distributions agreed well with calculated doses. Following this evaluation, treatments using the full energy scanning method were commenced in September 2015. [ABSTRACT FROM AUTHOR]

At Heavy Ion Medical Accelerator in Chiba (HIMAC) in National Institute of Radiological Sciences (NIRS), more than 9000 patients have been successfully treated by carbon ion beams since 1994. The successful results of treatments have led us to construct a new treatment facility equipped with a three-dimensional pencil beam scanning irradiation system, which is one of sophisticated techniques for cancer therapy with high energetic ion beam. This new facility comprises two treatment rooms having fixed beam lines and one treatment room having rotating gantry line. The challenge of this project is to realize treatment of a moving target by scanning irradiation. Thus, to realize this, the development of the fast scanning system is one of the most important issues in this project. After intense commissioning and quality assurance tests, the treatment with scanned ion beam was started in May 2011. After treatment of static target starts, we have developed related technologies. As a result, we can start treatment of moving target and treatment without range shifter plates since 2015. In this paper, the developments of the scanning irradiation system are described. [ABSTRACT FROM AUTHOR]

Abstract: For the quality assurance (QA) of therapeutic scanned carbon-ion beams, QA tool having high spatial resolution is required. The radiochromic film (such as Gafchromic EBT2 film model) is a very useful tool because of its high spatial resolution, self-development, and near tissue equivalence. However, for a complex field in carbon-ion therapy, it is difficult to unambiguously determine the dose from the measured net optical density (OD). As a first approach, we investigated the response of EBT2 to carbon-ion beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Japan. Based on the measured results, we performed QA measurements independently of dose. We verified the QA measurements by EBT2 by comparing the ionization chamber and the fluorescent screen. The results obtained with EBT2 were in good agreement with those obtained with the other detector. In addition, to test the use in a complex field, we verified the OD distributions for moving and static target by means of a gamma index analysis. As a result, we confirmed that EBT2 could be used as a part of QA procedures for therapeutic scanned carbon-ion beams. [Copyright &y& Elsevier]

Abstract: In order to realize a precise dose distribution in heavy-ion cancer therapy, high beam stability is required for the accelerator complex. Owing to load fluctuation caused by the upper ring, which is one of the two rings in HIMAC, current dips of ≈5–10Hz were observed in the power supply for the bending/quadrupole magnet of the other lower ring. The parameters of the beam stability, such as the spill variation, the beam position, and the size, were adversely affected by the current dips. In order to suppress these current dips, we developed a new feed-forward system in the magnet power supply. We verified the performance of the feed-forward system by measuring the suppression of the current dips. We also performed beam experiments to measure the variation of the horizontal tune and the structure of the beam spill, which is slowly extracted by the resonance method. The experimental result showed that the current dips were successfully reduced by the system to ΔI/I ∼10−6. It was also confirmed that the horizontal tune and the spill structure could be stabilized by the current dip suppression. [Copyright &y& Elsevier]

Three-dimensional (3D) pencil-beam scanning is an ideal irradiation technique to make the best use of the characteristics of a carbon-ion beam and to provide flexible dose delivery. To suppress beam spread due to multiple scattering and nuclear reactions, we developed a full energy scanning method. In some cases, such as eye treatments, the irradiation fields are very small and short ranged. Accordingly, we prepared a minimum low-energy carbon-ion beam corresponding to water-equivalent residual ranges of less than 2 mm. We performed experimental verification for low-energy carbon-ion beams ranging from 55.6 to 96.0 MeV/u. The accuracy of 3D dose delivery with the low-energy carbon-ion beam was verified by measuring the dose distributions for different target volumes. The results confirmed that the measured dose distributions agree well with the calculated ones. Then, the first eye treatment with low-energy carbon-ion beam to a patient was performed in 2018. [ABSTRACT FROM AUTHOR]

The HIMAC clinical study has been conducted with a carbon-ion beam since June 1994. Since 2006, as a new treatment research project, NIRS has developed both the accelerator and beam-delivery technologies for the sophisticated heavy-ion radiotherapy, which brings a pencil-beam 3D rescanning technology for both the static and moving-tumor treatments. In this technology, the depth-scanning technique was improved to the full-energy depth scanning by realizing a variable-energy operation of the HIMAC synchrotron itself. At present, a heavy-ion rotating gantry has been developed with the superconducting technology and is in a beam-commissioning stage. As a future plan, we just start a study of a multi-ions irradiation for more sophisticated LET-painting and a design study of a superconducting synchrotron for more compact heavy-ion radiotherapy facility. [ABSTRACT FROM AUTHOR]

A ridge filter (RGF), a beam energy modulation device, is usually used for particle radiotherapy with a pencil beam scanning system. The conventional RGF has a one-dimensional (1D) periodic laterally stepped structure in orthogonal plane with a central beam direction. The energy of a beam passing through the different thicknesses of the stepped RGF is modulated. Although the lateral pencil beam size is required to cover the several stepped RGF units to modulate its energy as designed, the current trend is to decrease lateral beam size to improve the scanning system. As a result, the beam size becomes smaller than the size of the individual RGF unit. The aim of this study was to develop a new RGF with two-dimensional (2D) honeycomb geometry to simultaneously achieve both a decrease in lateral beam size and the desired energy modulation. The conventional 1D-RGF and the 2D-RGF with honeycomb geometry were both designed so that the Bragg peak size of a 79 MeV/u carbon ion pencil beam in water was 1 mm RMS in the beam direction. To validate the design of the 2D-RGF, we calculated depth dose distributions in water using a simplified Monte Carlo method. In the calculations, we decreased the lateral pencil beam size at the entrance of the RGF and investigated the threshold of lateral beam size with which the pencil beam can reproduce the desired Bragg peak size for each type of RGF. In addition, we calculated lateral dose distributions in air downstream from the RGF and evaluated the inhomogeneity of the lateral dose distributions. Using the 2D-RGF, the threshold of lateral beam size with which the pencil beam can reproduce the desired Bragg peak size was smaller than that using the 1D-RGF. Moreover, the distance from the RGF at which the lateral dose distribution becomes uniform was shorter using the 2D-RGF than that using the 1D-RGF. These results indicate that when the periodic length of both RGFs is the same, the 2D-RGF allows use of a pencil beam with smaller lateral beam size and a shorter distance from the RGF to the target, resulting in improvement in the conformity of dose distribution in a tumor. [ABSTRACT FROM AUTHOR]

A superconducting rotating-gantry for carbon-ion radiotherapy was developed. This isocentric rotating gantry can transport carbon ions having the maximum kinetic energy of E = 430 MeV/ u to an isocenter with irradiation angles of over ±180°, and is further capable of performing three-dimensional raster-scanning irradiation. By using combined-function superconducting magnets, we could design a compact rotating gantry for carbon-ion radiotherapy. Construction of the gantry structure began since early 2014, and the installation of the entire gantry system to the Heavy Ion Medical Accelerator in Chiba (HIMAC) complex was completed by the end of September, 2015. Beam tuning subsequently began since October, 2015, and carbon ions, as accelerated by the HIMAC upper synchrotron, having kinetic energies of between E = 430–48 MeV/ u were successfully transported with the rotating gantry to the isocenter. The size and shape of the beam spots at the isocenter is being 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. [ABSTRACT FROM AUTHOR]

At National Institute of Radiological Sciences (NIRS), we have been commissioning a rotating-gantry system for carbon-ion radiotherapy. This rotating gantry can transport heavy ions at 430 MeV/u to an isocenter with irradiation angles of ±180° that can rotate around the patient so that the tumor can be irradiated from any direction. A three-dimensional pencil-beam scanning irradiation system equipped with the rotating gantry enables the optimal use of physical characteristics of carbon ions to provide accurate treatment. To ensure the treatment quality using such a complex system, the calibration of the primary dose monitor, output check, 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 Daily QA system. The system consists of an ionization chamber system and a scintillator system. The ionization chamber system is used for the calibration of the primary dose monitor, output check, and dose rate check, and the scintillator system is used for the range check, isocenter, and gantry angle. The performance of the Daily QA system was verified by a beam test. The stability of the output was within 0.5%, and the range was within 0.5 mm. The coincidence of the coordinates between the patient-positioning system and the irradiation system was verified using the Daily QA system. Our present findings verified that the new Daily QA system for a rotating gantry is capable of verifying the irradiation system with sufficient accuracy. [ABSTRACT FROM AUTHOR]

Controlling beam position in three-dimensional pencil-beam scanning is important because errors in beam position disturb the uniformity of irradiated dose distribution. To suppress this, we have developed a simple procedure for beamline tuning. Beamline tuning is performed with steering magnets and fluorescent screen monitors to converge a beam’s trajectory to a central orbit. The misalignment between beam position and a reference axis is determined through a verification system, which consists of a screen monitor and an acrylic phantom. If beam position deviates from the reference axis, two pairs of steering magnets, which are placed downstream of the beam transport line, correct the beam. These adjustments are iterated until the deviations for 11 energies of the beam are within 0.5 mm of the reference axis. To demonstrate the success of the proposed procedure, we used it to perform beam commissioning at the Kanagawa Cancer Center.
 [ABSTRACT FROM AUTHOR]

Abstract: The NIRS has carried out carbon-ion radiotherapy (RT) with HIMAC since 1994. On the basis of their ten-year HIMAC experience, NIRS has developed a standard-type CIRT facility in order to boost availability of carbon-ion RT in Japan. Work has been carried out at its pilot facility at Gunma University since 2010. The current projects of the pilot facility include Saga-HIMAT and i-ROCK, promoted by the Kanagawa prefectural cancer center. Toward the further sophisticated conformal carbon-ion RT with HIMAC, the NIRS has since 2006 been developing new treatment technologies, such as a fast 3D rescanning with a pencil beam and a compact rotating gantry. [Copyright &y& Elsevier]

Abstract: A flat radiation field for heavy ion beams is used in research experiments and clinical treatments. When a flat field is required, a beam spreading system must be installed for a beam line; thus a simple and affordable method is desirable. To achieve the carbon ion beam spreading, we employed a dual-ring double scattering method (DDSM), which consists of an initial scattering foil and a dual-ring subsequent scatterer. The scatterers for the DDSM were designed and tested to verify the flatness of the radiation field of the carbon ion beam. We obtained 100mm of the flat radiation field in the isocenter plane for the 2D radiation field, as expected. For the 3D radiation field, we obtained a field size of 80mm. With a 60-min setup time, using the DDSM system, and by placing only two scatterers, we can form the flat radiation field. [Copyright &y& Elsevier]