PurposeTo evaluate the accuracy of different dosimeters and the treatment planning system (TPS) for assessing the skin dose due to the electron streaming effect (ESE) on a 1.5 T magnetic resonance (MR)‐linac.MethodSkin dose due to the ESE on an MR‐linac (Unity, Elekta) was investigated using a solid water phantom rotated 45° in the x‐y plane (IEC61217) and centered at the isocenter. The phantom was irradiated with 1 × 1, 3 × 3, 5 × 5, 10 × 10, and 22 × 22 cm2 fields, gantry at 90°. Out‐of‐field doses (OFDs) deposited by electron streams generated at the entry and exit surface of the angled phantom were measured on the surface of solid water slabs placed ±20.0 cm from the isocenter along the x‐direction. A high‐resolution MOSkin™ detector served as a benchmark due to its shallower depth of measurement that matches the International Commission on Radiological Protection (ICRP) recommended depth for skin dose assessment (0.07 mm). MOSkin™ doses were compared to EBT3 film, OSLDs, a diamond detector, and the TPS where the experimental setup was modeled using two separate calculation parameters settings: a 0.1 cm dose grid with 0.2% statistical uncertainty (0.1 cm, 0.2%) and a 0.2 cm dose grid with 3.0% statistical uncertainty (0.2 cm, 3.0%).ResultsOSLD, film, the 0.1 cm, 0.2%, and 0.2 cm, 3.0% TPS ESE doses, underestimated skin doses measured by the MOSkin™ by as much as –75.3%, –7.0%, –24.7%, and –41.9%, respectively. Film results were most similar to MOSkin™ skin dose measurements.ConclusionsThese results show that electron streams can deposit significant doses outside the primary field and that dosimeter choice and TPS calculation settings greatly influence the reported readings. Due to the steep dose gradient of the ESE, EBT3 film remains the choice for accurate skin dose assessment in this challenging environment.

中文翻译：

---

1.5 T MR-Linac 上的电子流剂量测量和计算

目的评估不同剂量计和治疗计划系统 (TPS) 的准确性，用于评估 1.5 T 磁共振 (MR)-linac 上电子流效应 (ESE) 引起的皮肤剂量。方法 MR 上 ESE 引起的皮肤剂量‐直线加速器（Unity、Elekta）使用在 x-y 平面 (IEC61217) 上旋转 45° 并以等角点为中心的固体水模型进行研究。使用 1 × 1、3 × 3、5 × 5、10 × 10 和 22 × 22 cm 照射模型2场，龙门架呈 90°。在沿 x 方向距离等中心点 ±20.0 cm 放置的固体水板表面上测量了由成角度模型的入口和出口表面处产生的电子流沉积的场外剂量 (OFD)。高分辨率 MO皮肤™ 探测器因其较浅的测量深度而成为基准，符合国际放射防护委员会 (ICRP) 推荐的皮肤剂量评估深度 (0.07 毫米)。莫皮肤™ 剂量与 EBT3 胶片、OSLD、金刚石探测器和 TPS 进行比较，其中实验设置使用两个单独的计算参数设置进行建模：0.1 cm 剂量网格，具有 0.2% 统计不确定性（0.1 cm，0.2%）和 0.2 cm 剂量网格，统计不确定性为 3.0%（0.2 cm，3.0%）。结果OSLD、胶片、0.1 cm、0.2% 和 0.2 cm、3.0% TPS ESE 剂量，MO 测量的低估皮肤剂量皮肤™ 分别高达 –75.3%、–7.0%、–24.7% 和 –41.9%。胶片结果与 MO 最相似皮肤™ 皮肤剂量测量。结论这些结果表明，电子流可以在主场之外沉积大量剂量，并且剂量计的选择和 TPS 计算设置极大地影响报告的读数。由于 ESE 的剂量梯度陡峭，EBT3 胶片仍然是在这种充满挑战的环境中进行准确皮肤剂量评估的选择。