主动呼吸控制用于原发性肝癌放射治疗肝脏位置重复性的研究

背景与目的：呼吸运动能造成肝癌放疗靶区的扩大,限制了放疗剂量的增加.主动呼吸控制（active breathing control,ABC）提供了一种减少呼吸运动的简便方法,肝脏位置重复性较好是使用ABC技术减少靶区边界外放的一个重要前题,然而对使用该技术放疗过程中深吸气后肝脏位置的重复性目前尚不明确,因此本研究对ABC用于原发性肝癌放疗肝脏位置的重复性进行了测量.方法：入组本研究的患者共20人,其中16例肝癌碘油沉积良好.所有的患者进行了ABC呼吸训练和ABC控制下的放射治疗.在常规模拟机透视下测量一次屏气过程肝脏位置的稳定性和通过5次反复屏住吸气表示的一次放疗中肝脏位置的重复性.每周用兆伏级X线电子射野影像仪拍摄验证片与放疗计划生成的数字重建图像（digital reconstruction radiograph,DRR）比较测量分次放疗间肝脏位置在头脚方向上的重复性,通过每周在模拟机下体模固定在治疗体位拍摄正、侧位X线片,测量碘油在前后和左右位置上距离脊柱垂直距离的变化值,计算肝脏位置在这两个方向上的重复性.结果：所有患者配合良好,均能全程耐受ABC放疗屏气,没有1例因为不能耐受中断放疗.在平静呼吸状态下,患者膈在头脚方向上运动幅度平均为1.6 cm（范围：1.0～2.6 cm）.在透视下测得一次屏气过程中肝脏上下移动幅度平均为1.3 mm（范围：0.0～2.9 mm）.使用ABC放疗时一次放疗中和分次放疗间肝脏位置在头脚方向上的重复性（标准差）分别为1.6 mm和6.6 mm,前后方向上的重复性分别为0.9 mm和4.2 mm,左右方向上的重复性分别为0.7 mm和5.5 mm.结论：应用主动呼吸控制技术对入选的原发性肝癌患者放疗时肝脏的位置重复性良好.分次放疗间的重复性要差于一次放疗中的.安全的减少计划靶区的外扩需要结合影像引导的放疗并且要考虑肝脏位置的重复性.

Reproducibility of liver position using active breathing control for primary hepatocellular carcinoma radiotherapy

Background and purpose:Respiratory movement can increase planning target volume(PTV) of radiotherapy and result in the limitation of dose delivered to tumor.Active breathing control(ABC) provides a simple way to reduce respiratory motion.Immobilization of liver is an important premise to reduce the margin of planning target volume,but the reproducibility of liver position using ABC after deep inspiration is still unclear.The purpose of this study was to measure the reproducibility of liver position during radiotherapy.Methods:20 hepatocellular carcinoma patients were eligible for this study.16 of them had iodized oil deposited in the liver tumors.After breath training,the selected patients underwent CT simulation and radiotherapy with ABC.Intrabreath-hold liver stability was assessed using kV fluoroscopy during the breath-holding period.To measure intrafraction reproducibility of liver position relative to the vertebral bodies,patients were asked to inhale deeply and holding breath repeatedly for 5 times,then under simulator fluoroscope,the variation was obtained.Interfraction reproducibility of liver position in cranial-caudal direction was estimated by comparison of the variation of diaphragm between the digital reconstructive radiograph and weekly megavoltage verification images.Interfraction reproducibility of liver position in anterior-posterior and left-right direction was calculated by comparison of the variation of distance between the deposited iodized oil in the tumor and vertebral body through weekly X-graphs,respectively.Results:All patients were compatible with ABC technique and no one discontinued radiotherapy because of breath holding problem.Fluoroscopy revealed that the free breathing range of these patients was 1.6 cm(range 1.0-2.6 cm),and the average maximal liver motion during breathing-hold was 1.3 mm(range 0.0-2.9 mm).The average intrafraction and interfraction cranial-caudal reproducibility(standard deviation) of liver position relative to the vertebral bodies was 1.6 mm and 6.6 mm,in anterior-posterior direction the reproducibility was 0.9 mm and 4.2 mm,and in left-right direction that was 0.7 mm and 5.5 mm,respectively.Conclusions:The reproducibility of liver position is good in selected patients.However,interfracion reproducibility is worse than intrafraction reproducibility.It is rational to take the liver position reproducibility into account and apply image guidance during radiotherapy when considering the reduction of the planning target margin safely.