Wang Hao, Chen Hua, Gu Hengle, Shao Yan, Cai Xuwei, Fu Xiaolong, Xu Zhiyong
Department of Radiation Oncology, Shanghai Chest Hospital, Shanghai Jiao Tong University, Shanghai 200030, China.
Department of Radiation Oncology, Shanghai Chest Hospital, Shanghai Jiao Tong University, Shanghai 200030, China.
Med Dosim. 2018;43(1):46-54. doi: 10.1016/j.meddos.2017.08.002. Epub 2017 Oct 27.
Intensity-modulated radiotherapy (IMRT) is an important technology in cancer radiotherapy. In the current planning system, such as in the Pinnacle system, jaw positions are automatically set to cover all target volumes, and many medical centers in developing countries are not equipped with linear accelerators with a jaw tracing function. As solitary lesions are often located in patients, the resulting radiation leakage and transmission increase the dose exposure in surrounding critical organs, although blocked by multileaf collimator (MLC) leaves. We therefore designed a method to manually fix jaw positions, which further reduces doses. We particularly focused on the patients of peripheral lung cancer combined with mediastinal lymph node metastasis, as our medical center mainly targets lung cancer. We designed 2 treatment plans for each patient with the same optimization parameters, i.e., the plan of automatically chosen jaw positions (jaw auto-chosen plan) and the plan of fixed-jaw positions (fixed-jaw plan). In the latter plan, jaws were manually fixed for tumors in lung and in mediastinal lymph node metastases, respectively. We found that both plans met the clinical requirements, and the D, D, conformation number (CN), and homogeneity index (HI) for planning target volume (PTV) had no significant differences between the 2 plans. Importantly, the machine units (MUs) for fixed-jaw plans were 50%~60% more than routine jaw auto-chosen plans, whereas the V, V, V, V, and the mean dose in the total lung and the ipsilateral lung were less than the routine jaw auto-chosen plans. Dose-volume values D for the spinal cord and D, V, V for the heart existed no significant differences for 2 plans. In the fixed-jaw method, the total lung TLV-△V and TLV-△V values had a moderate positive correlation with the lung radiation leakage and the transmission area reduction. We concluded that the fixed-jaw plan is superior to the routine jaw auto-chosen plan in reducing the radiation exposure of surrounding critical organs, which will benefit the IMRT application.
调强放射治疗（IMRT）是癌症放射治疗中的一项重要技术。在当前的治疗计划系统中，如在Pinnacle系统中，颌部位置会自动设置以覆盖所有靶区，而发展中国家的许多医疗中心并未配备具有颌部跟踪功能的直线加速器。由于患者体内常出现孤立性病变，尽管有多叶准直器（MLC）叶片的阻挡，由此产生的辐射泄漏和透射仍会增加周围关键器官的剂量暴露。因此，我们设计了一种手动固定颌部位置的方法，可进一步降低剂量。我们特别关注周围型肺癌合并纵隔淋巴结转移的患者，因为我们医疗中心主要针对肺癌患者。我们为每位患者设计了2个具有相同优化参数的治疗计划，即自动选择颌部位置的计划（颌部自动选择计划）和固定颌部位置的计划（固定颌部计划）。在后者的计划中，分别针对肺部肿瘤和纵隔淋巴结转移手动固定颌部。我们发现这两个计划均符合临床要求，且计划靶区（PTV）的D、D、适形数（CN）和均匀性指数（HI）在这两个计划之间无显著差异。重要的是，固定颌部计划的机器跳数（MUs）比常规颌部自动选择计划多50%~60%，而全肺和同侧肺的V、V、V、V以及平均剂量均低于常规颌部自动选择计划。两个计划中脊髓的剂量体积值D以及心脏的D、V、V无显著差异。在固定颌部方法中，全肺TLV-△V和TLV-△V值与肺部辐射泄漏和透射面积减少呈中度正相关。我们得出结论，在减少周围关键器官的辐射暴露方面，固定颌部计划优于常规颌部自动选择计划，这将有利于IMRT的应用。
