Xia Wenlong, Zhang Ke, Li Minghui, Tian Yuan, Men Kuo, Wang Jingbo, Yi Junlin, Li Yexiong, Dai Jianrong
Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
Front Oncol. 2020 Sep 8;10:1739. doi: 10.3389/fonc.2020.01739. eCollection 2020.
This study investigates the impact of the magnetic field on plan quality and dose at the tissue-air interface in MR-guided radiotherapy of head and neck cancer.
The charts of 10 patients with hypopharyngeal carcinoma who were treated with conventional fractionated radiotherapy were collected and reviewed. The skin and tissues containing air cavities were contoured. Three plans using 9 fields of intensity-modulated radiation therapy were generated for each patient in the Monaco treatment planning system of an Elekta Unity MR-linac. The first plan was optimized without the magnetic field (plan). The second plan was recalculated in the presence of a 1.5-T magnetic field (plan) using the same segment shape and monitor units as the first plan. The third plan was reoptimized in the presence of a 1.5-T magnetic field (plan) using the same cost function as the first plan. The dose to the skin and tissues containing air cavities were compared across the three types of plans. A plan-quality metric method was used to evaluate the plan quality according to the clinical requirements.
The skin dose was increased in the presence of the 1.5-T magnetic field, and the amplitude increase of plan (ΔD 1.30 ± 0.42 Gy, ΔD 1.68 ± 1.36 Gy) was smaller than that of plan (ΔD 1.81 ± 0.79 Gy, ΔD 5.43 ± 2.26 Gy). There were no significant differences in terms of the metrics of interfaces of tissues containing air cavities except for an increased maximum dose to the larynx and trachea. The plan quality of plan (68.0 ± 9.2) was significantly worse than that of plan (82.2 ± 7.0), and the plan quality of plan (80.0 ± 7.0) was similar to that of plan.
The presence of a 1.5-T magnetic field had an apparent impact on the dose distribution, in particular, a significant increase in the skin dose. The plan quality of plan was similar to that of the original plan when the same cost function was used.
本研究调查磁场对头颈部癌磁共振引导放射治疗中组织-空气界面处计划质量和剂量的影响。
收集并回顾10例接受常规分割放射治疗的下咽癌患者的病历。勾勒出皮肤和含气腔的组织轮廓。在医科达Unity MR直线加速器的Monaco治疗计划系统中，为每位患者生成三个使用9野调强放射治疗的计划。第一个计划在无磁场情况下进行优化（计划1）。第二个计划在1.5T磁场存在的情况下重新计算（计划2），使用与第一个计划相同的射野形状和监测单位。第三个计划在1.5T磁场存在的情况下重新优化（计划3），使用与第一个计划相同的代价函数。比较三种类型计划中皮肤和含气腔组织的剂量。根据临床要求，采用计划质量指标方法评估计划质量。
在1.5T磁场存在的情况下，皮肤剂量增加，计划2（ΔD 1.30±0.42 Gy，ΔD 1.68±1.36 Gy）的增加幅度小于计划1（ΔD 1.81±0.79 Gy，ΔD 5.43±2.26 Gy）。除喉和气管的最大剂量增加外，含气腔组织界面的指标无显著差异。计划3（68.0±9.2）的计划质量明显低于计划2（82.2±7.0），计划2（80.0±7.0）的计划质量与计划1相似。
1.5T磁场的存在对剂量分布有明显影响，特别是皮肤剂量显著增加。当使用相同的代价函数时，计划3的计划质量与原计划相似。
