Kawata Kohei, Hirashima Hideaki, Nakata Manabu, Fujimoto Takahiro, Aizawa Rihito, Mizowaki Takashi
Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
Phys Med. 2025 Jan;129:104886. doi: 10.1016/j.ejmp.2024.104886. Epub 2025 Jan 2.
Free-breathing computed tomography (FBCT) used in treatment planning for lower thoracic (Th8-Th12) spine stereotactic body radiotherapy (SBRT) can cause deviations between planned and irradiated doses due to diaphragm movement (DM). This study analyzed the dosimetric impact of DM on lower thoracic spine SBRT.
Data were collected from 19 patients who underwent FBCT and four-dimensional CT (4DCT) during the same session. The 4DCT data were divided into ten respiratory phases (0-90%), and an average CT (AveCT) was reconstructed from them. Using FBCT, target and normal tissues near the diaphragm were contoured and spine SBRT plans with 24-Gy doses in two fractions were created. These plans were applied to each phase of CT and AveCT, with doses recalculated using the same parameters. Actual treatment doses (Deformed AveCT) were estimated by accumulating doses across each 4DCT phase using deformable image registration on the AveCT. Dose-volume histogram (DVH) indices were compared between the FBCT, AveCT, 0% phase, 50% phase, and Deformed AveCT plans.
The mean differences in DVH indices for target and normal tissues were within 2.4 and 2.1%, respectively, when the diaphragm displacement was between -1.6 cm and 2.0 cm, as compared with FBCT. DM displacement showed moderate to strong correlations with DVH differences.
Our results indicate that DM has a minor impact on DVH indices if the diaphragm remains within 1.5 cm of the FBCT position.
用于下胸椎（Th8-Th12）脊柱立体定向体部放疗（SBRT）治疗计划的自由呼吸计算机断层扫描（FBCT），由于膈肌运动（DM）可能导致计划剂量与照射剂量之间出现偏差。本研究分析了DM对下胸椎脊柱SBRT的剂量学影响。
收集了19例在同一疗程中接受FBCT和四维CT（4DCT）检查的患者的数据。4DCT数据被分为十个呼吸相位（0-90%），并从中重建出平均CT（AveCT）。使用FBCT对膈肌附近的靶区和正常组织进行轮廓勾画，并制定分两次给予24 Gy剂量的脊柱SBRT计划。这些计划应用于CT和AveCT的每个相位，并使用相同参数重新计算剂量。通过在AveCT上使用可变形图像配准在每个4DCT相位上累积剂量来估计实际治疗剂量（变形AveCT）。比较了FBCT、AveCT、0%相位、50%相位和变形AveCT计划之间的剂量体积直方图（DVH）指数。
与FBCT相比，当膈肌位移在-1.6 cm至2.0 cm之间时，靶区和正常组织的DVH指数平均差异分别在2.4%和2.1%以内。DM位移与DVH差异呈中度至强相关性。
我们的结果表明，如果膈肌保持在FBCT位置的1.5 cm范围内，DM对DVH指数的影响较小。
