即時適応放射線治療の現状と将来

The current status and future of online adaptive radiotherapy

日本放射線腫瘍学会のオンラインMR誘導適応放射線治療の実施ガイドライン^1）では，適応放射線治療とは，放射線治療中に腫瘍の縮小や患者の体重変化により，当初の治療計画では標的への線量が不十分になったり，周囲臓器への線量が増加することが懸念される場合に，放射線治療中に取得した患者の三次元医用画像に基づいて新しい治療計画を作成する放射線治療と定義されている。ESTRO物理ワークショップのパターン調査^2）では，適応放射線治療はその手法によって次の4つのカテゴリに分類されている。

Online adaptive radiotherapy is considered to be especially necessary for high dose prescriptions accurately such as stereotactic radiation therapy, especially in cases where the tumor is close to normal organs. One of the most important things in procedure of radiotherapy is the reproducibility of the radiation therapy position. If online adaptive radiotherapy is performed every time, there is almost no need to expect deviation in the position, and it is possible to set a radiation field that is truly concentrated on the tumor. However, at present, online adaptive radiotherapy takes about 30–60 minutes with MRI–based systems and 15–30 minutes with CBCT–based systems. To solve this issue, researches are being conducted on improving the accuracy of DIR and on automatic treatment planning and dynamic tracking using artificial intelligence（AI）.