粒子線治療装置と技術開発の現状：陽子線治療

Current status of proton therapy：equipment and technology development

粒子線治療は，その物理学的特徴から腫瘍に対する高い線量集中性と，正常組織の線量低減を同時に達成することができる。陽子線，重粒子線ともに米国で開始され，現在は国内外の多くの施設で粒子線治療が実施されている。粒子線治療の普及に伴い，治療実績が蓄積されるとともに，照射技術は目覚ましい発展をとげてきた。装置の小型化により普及が促進され，回転ガントリやスキャニング照射などの実用化により照射の自由度が向上し，より複雑な線量分布の形成が可能となった。近年は超高線量率照射（FLASH）が盛んに研究されており，実用化に向けて様々な開発が進められている。本稿では，粒子線治療の中でも施設数の多い陽子線治療に焦点を当て，その現状について紹介する。

Particle beam therapy can simultaneously achieve high dose convergence to tumors and dose reduction to normal tissues. Both proton and heavy ion beams were started in the United States. Today, particle therapy is being performed at many facilities worldwide including Japan. With the spread of particle therapy, treatment results have been accumulated and irradiation technology has made remarkable progress. The miniaturization of the equipment has promoted its spread. The practical application of rotating gantry and scanning irradiation has improved the degree of freedom of irradiation, making it possible to form more complicated dose distributions. In recent years, high-dose-rate irradiation（FLASH）has been actively studied. Various research and development are currently underway for its clinical use.

In this article, we focus on proton therapy and introduce its current status.