两种VMAT布野方式计划对胸中上段食管癌放疗的剂量学影响

Dosimetric Effects of Two Field Arrangenent Plans for VMAT on Radiotherapy for Upper and Middle Thoracic Esophageal Cancer

目的比较基于VMAT技术,采用两种布野方式对胸中上段食管癌进行计划设计的靶区、正常组织和计划质量的差异,以进一步寻找靶区剂量均匀和适形性更高、正常组织受量更低、计划质量更高的计划设计方式。方法对治疗的20例胸中上段食管癌放疗患者.固定技术采用头颈肩热塑面罩。靶区范围包括颈部淋巴结、食管癌原发灶和CTV,处方:GTV:60Gy/30F,CTV:54Gy/30F.使用Monaco5.1计划系统和蒙特卡洛算法进行剂量计算。两种布野方式:对穿弧(50°~310°,CCW,220°~140°,CCW)和单侧弧(180°~320°,CCW)进行计划设计。基于剂量直方图(DVH)和等剂量曲线分别对靶区的均匀指数(HI)、适形指数(CI)、肺(右肺,左肺,总肺)的V5和V20、脊髓的D2以及计划的机器跳数(MU)、控制点数(CP)进行统计分析。结果单侧弧靶区的HI和CI优于对穿弧。右肺的V5和V20对穿弧高于单侧弧,左肺的V20对穿弧高于单侧弧,V5低于单侧弧。脊髓的D2剂量对穿弧高于单侧弧。MU/CP对穿弧更高。结论对穿弧计划和单侧弧计划在剂量上均能满足临床治疗要求。单侧弧计划能够提供更好的靶区适形和均匀性,并且危及器官的受量更低。但是对于头颈肩热塑模固定技术,单侧弧布野技术,手臂在一定程度上受到剂量照射,并且手臂的位置活动度大,会导致剂量不精准。两种计划各有优势。因此,在临床上食管癌的计划设计应结合病人的病情和摆位技术个体化定制。

Objective To compare the differences of the target, normal tissue, and planning quality with two field arrangement methods in the treatment of upper and middle thoracic esophageal cancer based on VMAT, and further to find a treatment plan with higher target homogeneity and conformity, lower normal tissue dose acceptance and higher planning quality. Methods Twenty patients with upper and middle thoracic esophageal cancer were treated with the fixation method on the head and shoulder thermoplastic mask. The targets included the neck lymphatic, primary lesion and CTV. The prescription was GTV: 60 Gy/30 F and CTV: 54 Gy/30 F. Dose calculating was performed with Monaco 5.1 planning system and Monte Carlo algorithm. The field arrangement methods of two plans were opposite arc and unilateral arc. The angle of opposite arc was from 50 to 310 and 220 to 140 with CCW. The unilateral was 180 to 320 with CCW. The homogeneity index (HI) and conformity index (CI) of target were analyzed based on dose volume histogram (DVH) and isodose curve. The dose V5, V20 of lung (LungR, LungL, LungAll) and the D2 of spinal cord were also analyzed. The monitor units (MU) and control points (CP) of plan were counted to analyze the quality of plan. Results The plan of unilateral arc is better than opposite arc in the HI and CI of target. The plan of unilateral arc is lower to the V5 and V20 of the LungR, the V20 is also lower for the LungL. But for the V5 of LungL the plan of unilateral arc is higher. The plan of unilateral arc is lower for plan's MU. Conclusion Both the two plans meet clinical requirements. The plan of unilateral arc is better than opposite arc on the HI, CI of the target, the dose of the normal tissue, and the plan quality. But, the arm of patients has to suffer from dose in the plan of unilateral arc as the fixation method. As the arm is easy to move, it will affect the accuracy of the dose. So both plans have advantages. Thus, the plan design should depend on patient,s condition.