PURPOSE AND BACKGROUND 3D dosimetric verification of online adaptive workflows is essential as their complexity is unprecedented in radiation oncology. The aim of this work is to demonstrate the feasibility of back-projection portal dosimetry for 3D dosimetric verification of Unity MR-linac treatments. MATERIAL AND METHODS An earlier presented 2D back-projection algorithm for the Unity MR-linac geometry was extended for 3D dose reconstruction and comparison against planned dose distributions. 'In-air' as well as in-vivo portal EPID images can be used as input. The method was validated using data from treatments of 5 patients (2 rectal, 2 prostate cancer and one oligo metastasis). 3D pre-treatment verification of the reference plan using 'in-air' EPID images was performed and compared against measured (with the Octavius 4D system) and planned (in the planning CT) dose distributions. In-vivo EPID dose distributions were compared to the TPS for the first three adaptations of all treatments. For all comparisons, dose difference values at the reference point and γ-parameters were reported. RESULTS The comparison against the OCTAVIUS 4D system (3%, 2 mm, local) showed y-mean = 0.52 ± 0.10 and y-passrate = 91.9%, 95% CI [85.4, 98.4], and ΔDRP = -0.1 ± 1.1%. Pre-treatment verification against TPS data (3%, 2 mm, global) showed y-mean = 0.52 ± 0.04, y-passrate = 93.5%, 95% CI [92.4, 94.6] and ΔDRP = -0.9 ± 1.5%. The averaged y-results for the in-vivo 3D verification were y-mean = 0.52 ± 0.05, y-passrate = 92.5%, 95% CI [90.2, 94.8] and ΔDRP = 0.8 ± 2.1%. CONCLUSION 3D dosimetric verification of Unity MR-linac treatments using portal dosimetry is feasible, pre-treatment as well as in-vivo.

中文翻译：

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通过入口剂量测定法对 unity MR-linac 治疗进行 3D 剂量测定验证

目的和背景 在线自适应工作流程的 3D 剂量学验证至关重要，因为它们的复杂性在放射肿瘤学中是前所未有的。这项工作的目的是证明反投影门户剂量学在 Unity MR-linac 治疗的 3D 剂量学验证中的可行性。材料和方法 先前提出的 Unity MR-linac 几何的 2D 反投影算法被扩展用于 3D 剂量重建和与计划剂量分布的比较。“空中”和体内门户 EPID 图像可用作输入。该方法使用来自 5 名患者（2 名直肠癌、2 名前列腺癌和 1 名寡转移癌）的治疗数据进行验证。使用“空中”对参考计划进行 3D 预处理验证 执行 EPID 图像并将其与测量的（使用 Octavius 4D 系统）和计划的（在计划 CT 中）剂量分布进行比较。对于所有治疗的前三个适应，将体内 EPID 剂量分布与 TPS 进行比较。对于所有比较，报告了参考点和 γ 参数的剂量差异值。结果 与 OCTAVIUS 4D 系统（3%，2 mm，局部）的比较显示 y-mean = 0.52 ± 0.10 和 y-passrate = 91.9%、95% CI [85.4, 98.4] 和 ΔDRP = -0.1 ± 1.1% . 针对 TPS 数据（3%，2 毫米，全局）的治疗前验证显示 y 均值 = 0.52 ± 0.04，y 通过率 = 93.5%，95% CI [92.4, 94.6] 和 ΔDRP = -0.9 ± 1.5%。体内 3D 验证的平均 y 结果为 y-mean = 0.52 ± 0.05，y-passrate = 92.5%，95% CI [90.2, 94.8] 和 ΔDRP = 0.8 ± 2.1%。