PURPOSE This study aimed to quantify the coverage probability for esophageal cancer radiotherapy as a function of a preset margin for online MR-guided and (CB)CT-guided radiotherapy. METHODS Thirty esophageal cancer patients underwent six T2-weighted MRI scans, 1 prior to treatment and 5 during neoadjuvant chemoradiotherapy at weekly intervals. Gross tumor volume (GTV) and clinical target volume (CTV) were delineated on each individual scan. Follow-up scans were rigidly aligned to the bony anatomy and to the clinical target volume itself, mimicking two online set-up correction strategies: a conventional CBCT-guided set-up and a MR-guided set-up, respectively. Geometric coverage probability of the propagated CTVs was assessed for both set-up strategies by expanding the reference CTV with an isotropic margin varying from 0 mm to 15 mm with an increment of 1 mm. RESULTS A margin of 10 mm could resolve the interfractional changes for 118 out of the 132 (89%) analyzed fractions when applying a bone-match registration, whereas the CTV was adequately covered in 123 (93%) fractions when the registration was directly performed at the CTV itself (soft-tissue registration). Closer analyses revealed that target coverage violation predominantly occurred for distal tumors near the junction and into the cardia. CONCLUSION Online MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day.

中文翻译：

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MRI引导食管癌放疗的三维靶区覆盖评估

目的 本研究旨在量化食管癌放射治疗的覆盖概率，作为在线 MR 引导和 (CB)CT 引导放射治疗的预设边界的函数。方法 30 名食管癌患者接受了 6 次 T2 加权 MRI 扫描，1 次在治疗前进行，5 次在每周一次的新辅助放化疗期间进行。在每个单独的扫描中描绘总肿瘤体积 (GTV) 和临床目标体积 (CTV)。后续扫描与骨解剖结构和临床目标体积本身严格对齐，模拟两种在线设置校正策略：分别是传统的 CBCT 引导设置和 MR 引导设置。通过扩展参考 CTV 的各向同性边界从 0 毫米到 15 毫米，增量为 1 毫米，对两种设置策略的传播 CTV 的几何覆盖概率进行了评估。结果 在应用骨匹配配准时，10 毫米的边缘可以解决 132 个 (89%) 分析的馏分中 118 个的馏分间变化，而当直接进行配准时，CTV 被 123 (93%) 个馏分充分覆盖在 CTV 本身（软组织注册）。更仔细的分析表明，目标覆盖违反主要发生在交界处附近和进入贲门的远端肿瘤。结论与在线 CBCT 引导的骨匹配协议相比，在线 MR 引导的软组织配准协议表现出几何目标覆盖概率的适度改进。所以，