Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan City, China.
Technol Cancer Res Treat. 2024 Jan-Dec;23:15330338241227291. doi: 10.1177/15330338241227291.
Magnetic resonance (MR)-guided radiotherapy enables visualization of static anatomy, capturing tumor motion, and extracting quantitative image features for treatment verification and outcome monitoring. However, magnetic fields in online MR imaging (MRI) require efforts to ensure accurate dose measurements. This study aimed to assess the dosimetric impact of a 1.5 T magnetic field in esophageal cancer radiotherapy using MR-linac, exploring treatment adaptation potential and personalized medicine benefits. A prospective cohort study enrolled 100 esophageal squamous cell carcinoma patients undergoing 4DCT and 3DCT scans before radiotherapy. The heart was contoured on 3DCT, 4DCT end expiration (EE), and 4DCT end inhalation (EI) images by the same radiation oncologist. Reference RT plans were designed on 3DCT, with adjustments for different phases generating 5 plan types per patient. Variations in dose-volume parameters for organs at risk and the target area among different plans were compared using Monaco 5.40.04. Slight dose distortions at air-tissue interfaces were observed in the magnetic field's presence. Dose at air-tissue interfaces (chest wall and heart wall) was slightly higher in some patients (3.0% tissue increased by 4.3 Gy on average) compared to nonmagnetic conditions. Average clinical target volume coverage V100 dropped from 99% to 95% compared to reference plans (planEI and planEE). Dose-volume histogram variation between the original plan and reference plans was within 2.3%. Superior-inferior (SI) direction displacement was significantly larger than lateral and anterior-posterior directions ( < .05). Significant SI direction shift in lower esophageal cancerous regions during RT indicates the magnetic field's dosimetric impact, including the electron return effect at tissue-air boundaries. Changes in OAR dose could serve as valuable indicators of organ impairment and target dose alterations, especially for cardiac tissue when using the 1.5 T linac method. Reoptimizing the plan with the magnetic field enhances the feasibility of achieving a clinically acceptable treatment plan for esophageal cancer patients.
磁共振（MR）引导放射治疗能够可视化静态解剖结构，捕捉肿瘤运动，并提取定量图像特征，用于治疗验证和结果监测。然而，在线磁共振成像（MRI）中的磁场需要努力确保准确的剂量测量。本研究旨在评估使用 MR-直线加速器的 1.5T 磁场对食管癌放射治疗的剂量学影响，探索治疗适应的潜力和个性化医疗的益处。
一项前瞻性队列研究纳入了 100 例接受 4DCT 和放疗前 3DCT 扫描的食管鳞状细胞癌患者。由同一位放射肿瘤学家在 3DCT、4DCT 末期呼气（EE）和 4DCT 末期吸气（EI）图像上勾画心脏。在 3DCT 上设计参考 RT 计划，并针对不同相位进行调整，为每位患者生成 5 种计划类型。使用 Monaco 5.40.04 比较不同计划中危及器官和靶区的剂量-体积参数的变化。
在磁场存在的情况下，在空气-组织界面处观察到轻微的剂量扭曲。与非磁体条件相比，一些患者的空气-组织界面（胸壁和心脏壁）的剂量略高（平均增加 4.3Gy，组织增加 3.0%）。与参考计划（planEI 和 planEE）相比，平均临床靶区体积覆盖率 V100 从 99%下降到 95%。原始计划与参考计划之间的剂量-体积直方图变化在 2.3%以内。与侧向和前后方向相比，上下（SI）方向的位移明显更大（<0.05）。
在 RT 过程中，下段食管癌区域的 SI 方向明显移位，表明磁场的剂量学影响，包括组织-空气边界处的电子返回效应。OAR 剂量的变化可以作为器官损伤和靶区剂量改变的有价值指标，特别是在使用 1.5T 直线加速器方法时心脏组织的变化。在磁场下重新优化计划，增强了为食管癌患者实现临床可接受的治疗计划的可行性。
