Radiotherapy components of an magnetic resonnace‐guided radiotherapy (MRgRT) system can alter the magnetic fields, causing spatial distortion and image deformation, altering imaging and radiation isocenter coincidence and the accuracy of dose calculations. This work presents a characterization of radiotherapy component impact on MR imaging quality in terms of imaging isocenter variation and spatial integrity changes on a 0.35T MRgRT system, pre‐ and postupgrade of the system. The impact of gantry position, MLC field size, and treatment table power state on imaging isocenter and spatial integrity were investigated. A spatial integrity phantom was used for all tests. Images were acquired for gantry angles 0–330° at 30° increments to assess the impact of gantry position. For MLC and table power state tests all images were acquired at the home gantry position (330°). MLC field sizes ranged from 1.66 to 27.4 cm edge length square fields. Imaging isocenter shift caused by gantry position was reduced from 1.7 mm at gantry 150° preupgrade to 0.9 mm at gantry 120° postupgrade. Maximum spatial integrity errors were 0.5 mm or less pre‐ and postupgrade for all gantry angles, MLC field sizes, and treatment table power states. However, when the treatment table was powered on, there was significant reduction in SNR. This study showed that gantry position can impact imaging isocenter, but spatial integrity errors were not dependent on gantry position, MLC field size, or treatment table power state. Significant isocenter variation, while reduced postupgrade, is cause for further investigation.

中文翻译：

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表征放射治疗组件对 MRgRT 系统 MR 成像质量的影响


磁共振引导放射治疗（MRgRT）系统的放射治疗组件可以改变磁场，导致空间扭曲和图像变形，改变成像和辐射等中心重合以及剂量计算的准确性。这项工作从 0.35T MRgRT 系统、系统升级前和升级后的成像等中心变化和空间完整性变化方面描述了放疗组件对 MR 成像质量的影响。研究了机架位置、MLC 视野大小和治疗台功率状态对成像等角点和空间完整性的影响。所有测试均使用空间完整性模型。以 30° 增量采集机架角度 0–330° 的图像，以评估机架位置的影响。对于 MLC 和工作台电源状态测试，所有图像均在家庭龙门位置 (330°) 获取。 MLC 视野尺寸范围为 1.66 至 27.4 厘米边长方形视野。由机架位置引起的成像等中心偏移从机架 150° 升级前的 1.7 毫米减少到机架 120° 升级后的 0.9 毫米。对于所有机架角度、MLC 射野尺寸和治疗台功率状态，升级前后的最大空间完整性误差均为 0.5 毫米或更小。然而，当治疗台通电时，SNR 显着降低。这项研究表明，机架位置会影响成像等角点，但空间完整性误差并不依赖于机架位置、MLC 视野大小或治疗台功率状态。显着的等中心点变化虽然在升级后有所减少，但需要进一步研究。