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現在、国内で普及している重粒子線治療装置の敷地面積は非常に大きく、導入コストも大きい。そこで量子科学技術研究開発機構では超伝導電磁石の技術を利用したシンクロトロンの小型化や高強度レーザー技術を用いた加速入射器により既存の病院施設に設置できるサイズである次世代の小型重粒子治療装置「量子メス」の研究開発を進めている。量子メスの実現にあたり、入射器・シンクロトロンの小型化と共に加速器出口から照射エリアまでビーム輸送系(高エネルギービーム輸送系:HEBT)を短縮することが敷地面積を小さくするにあたり重要課題となる。本研究では回転ガントリーを採用した場合における回転ガントリー入口までのHEBT及び回転ガントリーの輸送系について検討を行った。 量子メスにおける治療では200段階以上のエネルギーのビームがシンクロトロンから供給され最大エネルギーは430 MeV/u、最低エネルギーは56 MeV/uである。HEBT及び回転ガントリーはすべての段数のビームエネルギーに対して最適な光学条件を満たす必要がある。本研究ではこの2つのエネルギー条件においてHEBT及び回転ガントリーの光学設計を行い、敷地面積の縮小化について検討を行った。本研究ではその現状について報告する。, 第17回日本加速器学会年会

We confirmed the effect of ion recombination using a parallel-plate ionization chamber: dose monitor for clinical use and the Advanced Markus chamber. A 290 MeV/u carbon-ion beam was irradiated using the continuous spot-scanning method in a field size of 5 cm by 5 cm with 2 mm spacing. We tested three beam intensities (1.35×10^8, 2.69×10^9, and 4.03×10^9 particle per second (pps)) at two linear energy transfers (12 keV/μm and 200 keV/μm). The charge (Q) was measured by changing the voltage of the Advanced Markus chamber and that of the dose monitor. Then, Boag’s method was used to calculate the saturated charge (Qsat ). For the Advanced Markus chamber, 300 V is a sufficient potential to collect charge. For the dose monitor, Qsat/Q at 2500 V was 1.024 for 4.03×10^9 pps, indicating that the general recombination correction cannot be ignored when high dose rate treatment is performed using a carbon-ion scanning beam.

Space travel has advanced significantly over the last six decades with astronauts spending up to 6 months at the International Space Station. Nonetheless, the living environment while in outer space is extremely challenging to astronauts. In particular, exposure to space radiation represents a serious potential long-term threat to the health of astronauts because the amount of radiation exposure accumulates during their time in space. Therefore, health risks associated with exposure to space radiation are an important topic in space travel, and characterizing space radiation in detail is essential for improving the safety of space missions. In the first part of this review, we provide an overview of the space radiation environment and briefly present current and future endeavors that monitor different space radiation environments. We then present research evaluating adverse biological effects caused by exposure to various space radiation environments and how these can be reduced. We especially consider the deleterious effects on cellular DNA and how cells activate DNA repair mechanisms. The latest technologies being developed, e.g., a fluorescent ubiquitination-based cell cycle indicator, to measure real-time cell cycle progression and DNA damage caused by exposure to ultraviolet radiation are presented. Progress in examining the combined effects of microgravity and radiation to animals and plants are summarized, and our current understanding of the relationship between psychological stress and radiation is presented. Finally, we provide details about protective agents and the study of organisms that are highly resistant to radiation and how their biological mechanisms may aid developing novel technologies that alleviate biological damage caused by radiation. Future research that furthers our understanding of the effects of space radiation on human health will facilitate risk-mitigating strategies to enable long-term space and planetary exploration.

Previous studies have revealed application of a magnetic field longitudinal to a carbon-ion beam enhances its biological effectiveness. This communication investigated how timing of the magnetic field application with respect to beam irradiation influenced this effect. Human cancer cells were exposed to carbon-ion beams with linear energy transfer (LET) of 12 and 50 keV/μm. The longitudinal magnetic field of 0.3 T was applied to the cells just before, during, or right after the beam irradiation. The effects of the timing on the biological effectiveness were evaluated by cell survival. The biological effectiveness increased only if the magnetic field was applied during beam irradiation for both LET beams.

光速の70%程度まで加速された炭素イオンは、線量集中性の良さとX線・陽子線の2～3倍に達する生物学的効果をもつことから、これをがん治療に使用する重粒子線治療は、いくつかの疾患で手術に匹敵する局所制御を実現している。また、一部疾患では1日1時間以内で治療が終わることから、量子ビームによる切らない手術とも言える。治療装置も最近では3次元スキャニング照射装置と回転ガントリー装置の組み合わせにより強度変調照射が可能になるなど、他の放射線治療装置と比べても技術的な遜色はなくなっている。しかしながら、重粒子線治療施設は国内に6施設しかなく、世界的にも12施設にとどまっている。その主な原因は加速器を含めた治療装置を設置するために必要な施設が依然として65m×45m程度と大きく、巨額な初期投資が必要なことにある。（図1参照）。この課題の克服のためには、病院内の治療室に設置可能で低コストの治療装置が必須である。また、現在の重粒子線治療では、1日で治療が終わる疾患もあれば、治療期間の長い疾患（4週間～5週間）も存在する。受け入れ可能患者数を増やすためにも、治療成績向上だけでなく、治療期間の短期化を含めた高度化が求められている。 2016年4月に日本原子力研究開発機構の一部と放射線医学総合研究所が一緒になって誕生した量子科学技術研究開発機構（以下、量研）は、重粒子線治療の研究・臨床実績だけでなく、超伝導・レーザー・量子ビームなど先端的な量子科学技術の研究開発能力をもつ組織であることから、これを活かして2017年より次世代の重粒子線治療装置を「量子メス」と名付けて開発を実施している。

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.

粒子線がん治療は、加速器によって水素イオン（陽子）や炭素イオン（重粒子）などの荷電粒子を光速近くまで加速し、体内のがん細胞に照射して死滅させる治療法である。荷電粒子は高速で通過する皮膚近辺よりも、体内の停止点近辺で最大の線量を与えるという特性をもっている（発見者にちなんでBraggピークと呼ばれる）。例えば、光速の70%の速度をもった炭素イオンは、体内を25 cm程度走って停止する。この特性を活かし、がんの位置に荷電粒子が止まるように、荷電粒子の速度を調整することで、がんに線量を集中させている。特に、炭素イオンは陽子に比べると重いため、体内でも散乱されずに直進し、周囲の臓器の被ばくが少なく、副作用が小さいという利点をもっている。さらに炭素イオンの持つ高い生物効果は、放射線に耐性を持ったがんに対しても有効であることが知られている。 こうした重粒子線（炭素線）の優れた特性を臨床で実証するために、世界初の重粒子線治療用加速器であるHIMAC（Heavy Ion Medical Accelerator in Chiba）が、放射線医学総合研究（以下、放医研）に建設され、1994年から治療が開始された[1]。図1に示すように、現在までにHIMACにおける炭素線治療件数は11,000件を超えており、多くのがんにおいて良好な成績を得ている。特に、前立腺、手術不能な骨・軟部がん、頭頸部がんについては、その実績から保険診療が認められており、現在全体の6割程度の炭素線治療が保険診療として実施されている。一方、肺、膵臓、肝臓、直腸術後再発、婦人科などのがんについては、先進医療制度を利用した炭素線治療とデータ集積が行われており、近い将来の保険収載が期待されている。また、放医研では炭素線の線量集中性の良さを活かし、肺がんは1日、肝臓がんは2日で治療が完了しており、前立腺がんも4日で完了させるなど治療の短期化に向けた臨床研究も進めている。

Purpose: Our previous study revealed application of a magnetic field longitudinal to a carbon-ion beam of 0.1 ≤ B// ≤ 0.6 T enhances the biological effectiveness of the radiation. The purpose of this study is to experimentally verify whether application of a magnetic field perpendicular to the beam also alters the biological effectiveness. Methods and Materials: Most experimental conditions other than the magnetic field direction were the same as those used in the previous study to allow comparison of their results. Human cancer and normal cells were exposed to low (12 keV/μm) and high (50 keV/μm) linear energy transfer (LET) carbon-ion beams under the perpendicular magnetic fields of = 0, 0.15, 0.3, or 0.6 T generated by a dipole magnet. The effects of the magnetic fields on the biological effectiveness were evaluated by clonogenic cell survival. Doses that would result in the survival of 10%, D10s, were determined for the exposures and analyzed using Student’s t-tests. Results: For both cancer and normal cells treated by low- and high-LET carbon-ion beams, the D10s measured in the presence of the perpendicular magnetic fields of ≥ 0.15 T were not statistically different (p >> 0.05) from the D10s measured in the absence of the magnetic fields, = 0 T. Conclusions: Exposure of human cancer and normal cells to the perpendicular magnetic fields of ≤ 0.6 T did not alter significantly the biological effectiveness of the carbon-ion beams, unlike the exposure to longitudinal magnetic fields of the same strength. Although the mechanisms underlying the observed results still require further exploration, these findings indicate that the influence of the magnetic field on biological effectiveness of the carbon-ion beam depends on the applied field direction with respect to the beam.

The National Institute of Radiological Sciences in Japan started clinical studies of carbon-ion radiotherapy (CIRT) in 1994. Due to the high linear energy transfer of highly charged particles, carbon-ion beams show high relative biological effectiveness in cell killing, especially at the Bragg peak of dose near the beam range, which is controlled to conform to a tumor. Recent technological developments for CIRT include fast pencil-beam scanning, fluoroscopic respiratory motion management, advanced beam modeling for treatment planning, and a superconducting rotating gantry, which have contributed to accuracy, precision, and conformation of dose, operational efficiency, and patient comfort. With technological maturity, CIRT facilities are rapidly increasing in Asia and Europe. Ongoing developments include extension to multiple ion species and facility downsizing to raise the quality and availability of ion-beam therapy in medical care.

Purpose: A magnetic field longitudinal to an ion beam will potentially affect the biological effectiveness of the radiation. The purpose of this study is to experimentally verify the significance of such effects. Methods and Materials: Human cancer and normal cell lines were exposed to low (12 keV/μm) and high (50 keV/μm) linear energy transfer (LET) carbon-ion beams under the longitudinal magnetic fields of B// = 0, 0.1, 0.2, 0.3, or 0.6 T generated by a solenoid magnet. The effects of the magnetic fields on the biological effectiveness were evaluated by clonogenic cell survival. Doses that would result in a survival fraction of 10% (D10s) were determined for each cell line and magnetic field. Results: For cancer cells exposed to the low (high)-LET beams, D10 decreased from 5.2 (3.1) Gy at 0 T to 4.3 (2.4) Gy at 0.1 T, while no further decrease in D10 was observed for higher magnetic fields. For normal cells, decreases in D10 of comparable magnitudes were observed by applying the magnetic fields. Conclusions: Significant decreases in D10, i.e., significant enhancements of the biological effectiveness, were observed in both cancer and normal cells by applying longitudinal magnetic fields of B// ≥ 0.1 T. These effects were enhanced with LET. Further studies are required to figure out the mechanism underlying the observed results.

量研では，「がん死ゼロの健康長寿社会」の実現のために，量研・放医研が中心となって開発してきた重粒子線がん治療装置を，大幅に小型化・低価格化すると共に，日帰りがん治療を一般化できるように高度化する，次世代の治療装置である「量子メス」の開発に着手した。本稿では，その量子メスの概要を紹介する。