Search

The effect of a magnetic field loaded parallel to the ion-beam track on the generations of reactive oxygen species (ROS) in water was investigated. It was reported that loading magnetic field parallel to the particle beam track exaggerate the biological effects, i.e. cell lethality, of the particle beam. However, the mechanism of the enhanced cell death delivered by a logigudinal magnetic field to the beam track has not been clarified yet. Local density of •OH generation was estimated by a method based on EPR spin-trapping technique. A series of reaction mixtures containing varying concentrations (0.76‒2278 mM) of DMPO was prepared, and transferred to a polyethylene bag for irradiation. Then, the samples were irradiated 16 Gy of carbon- or iron-beam at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan) with or without longitudinal magnetic field (0.0, 0.3, or 0.6 T). O2-dependent and O2-independent H2O2 yield was measured. An aliquot of ultra-pure water was irradiated by carbon-ion beam with or without longitudinal magnetic field. Irradiation experiments were performed under air or hypoxic (<0.5% oxygen) conditions. H2O2 generations in irradiated water samples were quantified by an EPR spin-trapping method, which measures •OH synthesized from H2O2 by the UVB irradiation. Relatively sparse •OH generations caused by particle beams in waster were not affected with loading magnetic field on beam track. Oxygen dependent H2O2 generation was decreased and oxygen-independent H2O2 generation was increased under loading magnetic field parallel to the beam track. Loading magnetic field parallel to the beam track could make •OH generation denser, or could make reaction of dense •OH increased., 20th Biennial Meeting of SFRR International (SFRR-I 2021)

The multi-ion radiotherapy with dose distribution and Liner Energy Transfer optimization is being studied at QST. Helium, carbon, oxygen and neon ions are considered as ion species for multi-ion therapy. A basic experiment using these ion beams has been carried out at the HIMAC. For heavy-ion radiotherapy facility, it is desirable to operate with only one ECR ion source. We considered the operating method with only one ion source for multi-ion radiotherapy. Ionization gases were helium, methane, oxygen, and neon to produce He2+, C4+, O6+ and Ne7+ ions. Requirement values of beam current were 940 µA correspond to He2+, 290 µA to C4+, 330 µA to O6+, and 245 µA to Ne7+, respectively. This value was obtained from the number of particles required for the cancer treatment and the transmission efficiency of the accelerator in the HIMAC. We performed some beam tests for design of a new compact ion source with the existing 18 GHz ECR ion source (NIRS-HEC). From the results of the beam tests, we estimate the mirror magnetic field of NIRS-HEC by using POISSON/SUPERFISH code. Then, the structure of the permanent magnets for new ECR ion source is determined so that they reproduce the values of the upstream mirror peak (Binj), B minimum (Bmin) and the downstream mirror peak (Bext) at the NIRS-HEC. The magnetic field of Binj, Bmin and Bext at NIRS-HEC were 1.14 T, 0.475 T and 0.9 T, respectively. We will describe about the beam tests with the NIRS-HEC and design of the new compact ECR ion source.

Track-structure Monte Carlo simulations are useful tools to evaluate initial DNA damage induced by irradiation. In the previous study, we have developed a Gean4-DNA-based application to estimate the cell surviving fraction of V79 cells after irradiation, bridging the gap between the initial DNA damage and the DNA-rejoining kinetics by means of the two-lesion kinetics (TLK) model. However, since the DNA repair performance depends on cell line, the same model parameters cannot be used for the different cell lines. Thus, we extended the Geant4-DNA application with an updated TLK model for the evaluation of DNA damage repair performance in HSGc-C5 carcinoma cells which are typically used for evaluating proton/carbon radiation treatment effects. For this evaluation, we also performed experimental measurements for cell surviving fractions and DNA-rejoining kinetics of the HSGc-C5s cells. Concerning fast- and slow-DNA rejoining, the TLK model parameters were adequately optimized with the simulated initial DNA damage. Using the optimized TLK model, the Geant4-DNA simulation is now able to predict cell survival and DNA-rejoining kinetics for HSGc-C5s cells.

The effects of a magnetic field longitudinal to the ion beam track on the generation of hydroxyl radicals (•OH) and hydrogen peroxide (H2O2) in water were investigated. A longitudinal magnetic field was reported to enhance the biological effects of the ion beam. However, the mechanism of the increased cell death by a longitudinal magnetic field has not been clarified. The local density of •OH generation was estimated by a method based on the EPR spin-trapping. A series of reaction mixtures containing varying concentrations (0.76‒2278 mM) of DMPO was irradiated by 16 Gy of carbon- or iron-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan) with or without a longitudinal magnetic field (0.0, 0.3, or 0.6 T). The DMPO-OH yield in the sample solutions was measured by X-band EPR and plotted versus DMPO density. O2-dependent and O2-independent H2O2 yields were measured. An aliquot of ultra-pure water was irradiated by carbon-ion beams with or without a longitudinal magnetic field. Irradiation experiments were performed under air or hypoxic conditions. H2O2 generation in irradiated water samples was quantified by an EPR spin-trapping, which measures •OH synthesized from H2O2 by UVB irradiation. Relatively sparse •OH generation caused by particle beams in water were not affected by loading a magnetic field on the beam track. O2-dependent H2O2 generation decreased and oxygen-independent H2O2 generation increased after loading a magnetic field parallel to the beam track. Loading a magnetic field to the beam track made •OH generation denser or made dense •OH more reactive.

An electron cyclotron resonance (ECR) ion source (ECRIS) can generate an available amount of multicharged ions, thus it is not limited for use in the field of accelerator science, but also in medical/biological fields, such as for heavy ion beam cancer treatment and ion engines. The processes of generating multicharged ions are mainly sequential collisions of a direct ionization process by electrons, and have good ion confinement characteristics. By utilizing this confinement property, we have synthesized iron-encapsulated fullerenes, which are supramolecular and can be expected to have various high functions. Fullerenes and iron ions are vaporized from pure solid materials and introduced into the ECRIS together with the support gas. We investigated conditions under which fullerene ions do not dissociate and iron ions are generated so that both can coexist. Generated ions are extracted from the ECRIS and separated by mass/charge with a dipole magnet, and detected with a Faraday cup. This measurement system is characterized by a wide dynamic range. The charge-state distribution (CSD) of ion currents was measured to investigate the optimum conditions for supramolecular synthesis. As a result, a significant spectrum suggesting the possibility of iron-encapsulated fullerenes was obtained. This paper describes the details of these experimental results

Several research and developments have been performed at a compact ECR ion source (Kei3) with a fixed magnetic field at HIMAC. The Kei3 is a testing machine for application of Kei series developed for high-energy carbon-ion radiotherapy. It is difficult for Kei3 to produce ions that are heavier than carbon ion because it uses the same magnetic field distribution as the Kei series. In order to improve the beam current of multiply charged ions such as the neon and the argon, the two microwave frequency heating method was tested in Kei3. Microwaves are introduced from the vacuum box on the upstream side of the plasma chamber through the rectangular waveguide of the WR-90. A traveling wave tube (TWT) amplifier made by NEC (LD79X75A1) is used as the microwave source. The frequency band is 9.75-10.25 GHz and the maximum output power is 750 W. The WR-75 waveguide is also introduced from the upper part of the upstream vacuum box and installed on top of the existing WR-90 waveguide. A TWT amplifier manufactured by Xicom (XTRD-300IJ) was used as a microwave source for the two frequency heating. The frequency band is 10-18 GHz and the maximum output power is 300 W. A beam test with oxygen, neon, and argon was performed in order to confirm the effect of two microwave frequency heating. In this test, we focused on O6+, Ne7+, and Ar9+ ions. We checked the microwave frequency at the XTRD-300IJ, dependence of the microwave power at the LD79X75A1 and charge state distributions of O, Ne and Ar.

A new compact electron-beam ion source (EBIS) with a low-energy hollow electron beam has been designed to produce ions for use in heavy-ion therapy. Numerical analyses of the electron beam using the three-dimensional particle-in-cell method determine the appropriate shape of the inner electrodes to realize a compact size and a sufficient number of confined ions for heavy-ion therapy. The analyses also show that the undesirable instability of the hollow electron beam is mitigated by the reflection mode with an electron repeller. Experimental tests were performed on the assembled EBIS to assess the validity of its design. The results of an electron-beam test show that the electrodes have been designed appropriately. Additionally, the results of an ion-beam test show that ions can be produced and confined in the newly developed compact EBIS and the number of extracted ions is just shy of the target value, showing the prospects of modifications aimed at realizing a compact EBIS specialized for the production of ions used in heavy-ion therapy.

High-energy carbon-ion radiotherapy is being carried out at Heavy Ion Medical Accelerator in Chiba (HIMAC). Over 12000 cancer patients have been treated with carbon beams having energies of between 56-430 MeV/u since 1994. There are two injectors in the HIMAC for medical and experimental use. First injector consists of two ECR ion sources and one PIG ion source, the RFQ linac and the DTL. Usually, this injector suppling the carbon ion for cancer therapy and various ion such as H, He, Fe, Xe are accelerated for biological and physical experiment. The 10 GHz NIRS-ECR ion source produce the carbon ion for cancer therapy. The 18 GHz NIRS-HEC ion source produce He to Xe ions for experimental use. Second injector consists of the compact ECR ion source with all permanent magnet, the RFQ linac and the APF IH-DTL. This injector supplies the carbon ion for experimental use. Additionally, we tried production of the Indium and the Tin ions by using the In(C5H5) and the Sn(i-C3H7)4 at the NIRS-HEC. Beam current of the 115In20+ and 120Sn18+ were 90 and 15 microA, respectively., 24th International Workshop on ECR Ion Sources