UnityによるMR画像誘導即時適応放射線治療

MR–guided online adaptive radiotherapy with 1.5 T MR–Linac, Elekta Unity

強度変調放射線治療（intensity–modulated radiation therapy：IMRT）や定位放射線治療，画像誘導放射線治療（image–guided radiotherapy：IGRT）など高精度放射線治療技術の進歩により，空間的に理想的な放射線を照射する精度は革新的に向上した。一方で，治療期間中の標的およびリスク臓器の体積変化や変形といった非剛体性変化への対応は困難なため，計画時の理想的な線量分布と患者体内に投与される線量分布には乖離が生じることになる。

We have applied MR–guided on–line adaptive radiotherapy clinically using 1.5 T MR–linac, Elekta Unity, since May 2022. The Unity can clearly visualize all anatomical changes during the course of radiotherapy and hence adapt the treatment plan to deliver the optimal dose distribution for patients every day. However, there is a trade–off between the dosimetric gain and the risk of on–line treatment planning or the time spent for adapting the treatment plan. Here, we provide our experience of MR–guided on–line adaptive radiotherapy using the Unity.