通常照射法におけるセットアップエラーおよび体型変化が線量分布に及ぼす影響についての検討

摘要

The purpose of this study was to evaluate the impact of setup error and anatomical change on dose distribution during conventional radiation therapy. We performed regional irradiation (Planl) using opposing pair fields, and then we planned local irradiation (Plan2) with a computed tomography (CT) acquired at that time in 10 patients with advanced oral cancer. To consider the setup error, a minimum dose of gross tumor volume (GTV) and a maximum dose for the spinal cord were re-calculated with isocenter shifts of +5 mm. We also evaluated an alteration of reference dose due to anatomical changes during radiation therapy. A minimum dose of GTV was decreased with isocenter shifts; the trend was stronger in Plan2 than Planl (-5.7% vs. -1.2%, p=0.02). Similarly, a maximum dose of spinal cord was increased with isocenter shifts, especially in Plan2 (12.2% vs. 0.5%, p<0.01). Anatomical changes during radiation therapy were observed in all patients, and the mean difference for depth was -4 mm in Planl; the reference dose was increased in Planl and Plan2. Precise setup is necessary, especially for local irradiation in spite of anatomical changes during radiation therapy. Reimaging and replanning are recommended for patients with marked anatomical changes.%放射線治療において，位置合わせの再現性は照射体積および線量分布に影響を与える要素の一つであり，毎回の照射では厳密なセットアップが求められる．特に，定位照射（stereotactic irradiation；STI）や強度変調放射線治療（intensity modulated radiation therapy;IMRT）ではセットアップの精度が重要であり，画像誘導放射線治療（image guided radiotherapy；IGRT）が不可欠と考えられている）.