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目的:初步观察MR引导下非小细胞肺癌体部立体定向放疗(SBRT)的可行性，并对有无磁场环境下剂量学差异进行分析。方法:前瞻性的入组3例SBRT的非小细胞肺癌患者，均应用MR引导加速器放疗。治疗计划分别应用有磁场模型和无磁场模型进行优化和剂量计算，同时在常规加速器进行患者备用计划的制备。比较有无磁场模型剂量的分布差异。同时对靶区覆盖度、计划通过率、治疗时间进行描述，并比较常规加速器备用计划和有磁场模型下执行计划的复杂度等差异。结果:3例患者分次治疗时间为(36.67±6.11) min，在线自适应计划平均时间为(14.4±1.7) min，患者基本耐受。治疗前计划的γ通过率(3%/3 mm)平均为98.9%，疗中在线计划γ通过率(3%/3 mm)为98.5%，靶区覆盖度达99.1%，满足临床需求。有磁场情况下肺部低剂量区剂量略低于无磁场情况，但肋骨和皮肤剂量因磁场存在略高于无磁场计划。在线自适应计划的机器跳数略高于参考计划，常规加速器备用计划机器跳数在相同靶区覆盖度情况下明显低于MR加速器计划。随访结果显示患者无不良反应，近期疗效均为部分缓解。结论:在考虑磁场影响情况下可获得满足临床需求的治疗计划，证明MR加速器引导的肺癌SBRT放疗具有可行性，但治疗时间较长，治疗流程较为复杂。“,”Objective:To observe the feasibility of magnetic resonance (MR)-guided stereotactic body radiotherapy (SBRT) for non-small cell lung cancer, and analyze the dosimetric differences in the presence or absence of magnetic field.Methods:Three patients with non-small cell lung cancer were prospectively treated with MR-guided linac (MR linac) for SBRT, and the dose was calculated with or without magnetic field models. The differences of dose distribution with or without magnetic field models were compared. At the same time, the target coverage, plan pass rate and treatment time were described, and the complexity of the conventional accelerator backup plan and the magnetic field model were compared.Results:The treatment time of 3 patients was (36.67±6.11) min, and the average time of online adaptive planning was (14.4±1.7) min, which was basically tolerated by patients. The treatment plan pass rate (3%/3 mm) was 98.9%, the Gamma pass rate (3%/3 mm) of the online plan during treatment was 98.5% and the target coverage was 99.1%, which met the clinical needs. The dose in the low dose area of the lung was slightly lower than that in the case without magnetic field, whereas the dose in ribs and skin was slightly higher than that in the plan without magnetic field. The number of machine unit (MU) for online adaptive plan was slightly higher than that of the reference plan, and the number of MU for the conventional accelerator standby treatment plan was significantly lower than that of the MR linac plan under the same target coverage. The follow-up results showed that there was no adverse reaction, and the short-term efficacy was partially relieved.Conclusions:In the case of considering the influence of magnetic field, the treatment plan meeting the clinical needs can be obtained. It is proven that SBRT radiotherapy for lung cancer guided by magnetic resonance accelerator is feasible, whereas the treatment time and process are complex.