Biological dose estimation for charged-particle therapy using an improved PHITS code coupled with a microdosimetric kinetic model

改良版PHITSとマイクロドジメトリを組合せた粒子線治療における生物学的線量評価

佐藤 達彦   ; 加瀬 優紀*; 渡辺 立子; 仁井田 浩二*; Sihver, L.*

Sato, Tatsuhiko; Kase, Yuki*; Watanabe, Ritsuko; Niita, Koji*; Sihver, L.*

従来、別々に研究されてきたマイクロドジメトリとマクロドジメトリの知見を融合し、粒子線治療における新たな生物学的線量評価法を構築した。具体的には、マイクロドジメトリ分野で放射線種の違いによる生物効果比(RBE)を表すために利用されてきたLineal Energyの概念をマクロドジメトリ分野で利用されてきた粒子線輸送計算コードPHITSに組み込み、従来の計算コードでは評価できなかった、粒子線治療による腫瘍部や正常組織など巨視的な空間内における細胞生存率を計算可能とした。この成果は、粒子線治療における治療計画の最適化に有用なだけでなく、航空機乗務員や宇宙飛行士の宇宙線被ばくによる健康影響の評価精度向上に多大に貢献できるものである。

A new method for estimating biological dose from charged-particle therapy was established, using the improved PHITS coupled with a microdosimetric kinetic model. In the method, the biological dose can be determined by multiplying the physical dose by the RBE for a surviving fraction of tumor cells, which is estimated from the saturation-corrected dose-mean lineal energy y* calculated by the improved PHITS. The accuracy of the biological dose estimated by this method was reliably verified by comparing the calculated physical doses and RBE values with the corresponding experimental data obtained by irradiating a slab phantom with the spread-out Bragg peak beams as well as several types of mono-energetic HZE particles. The simulation technique established in this study will help to optimize the treatment planning of charged-particle therapy for maximizing the therapeutic effect on tumor while minimizing unintended harmful effects on surrounding normal tissues.