直线加速器二级准直器在全段食管癌术后调强计划中的应用

目的:探讨全段食管癌术后放疗患者调强计划中限制二级准直器位置对靶区和危及器官受照剂量的影响。方法:选择13例全段食管癌术后放疗患者，设计两种逆向调强放疗（IMRT）计划。第一种是二级准直器限制位置的IMRT（Jaw Fixed-IMRT,F-IMRT）:以心脏上下界为界，F-IMRT计划的靶区分为上、中、下三个分区，通过固定二级准直器来实现，三个分区分别设计射野数量及角度，两两分区之间二级准直器头脚方向重叠(overlap,OL)的距离定为0、1、2、3、4 cm，共生成5个F-IMRT计划（命名为F-IMRT-OL0.1.2.3.4）;第二种是常规IMRT(conventional-IMRT,C-IMRT):患者靶区为一个整体，不限制二级准直器，射野设置为9野共面均分。两种计划靶区及危及器官优化参数相同，对比分析两种计划的剂量学差异及加速器跳数（MU）。结果:F-IMRT计划中，二级准直器需要重叠以保证靶区足量，但随重叠距离增加危及器官受量呈递增趋势，本研究中F-IMRT-OL1为最优计划。F-IMRT-OL1与C-IMRT计划的适形指数（CI）和均匀性指数（HI）差异无统计学差异（P＞0.05）；F-IMRT-OL1肺的V5 Gy、V10 Gy、V20 Gy及Dmean低于C-IMRT，具有统计学差异（P＜0.05），而对于肺的高剂量体积V30 Gy，无明显差异（P＞0.05）；F-IMRT-OL1计划心脏的V30 Gy和V40 Gy及Dmean均低于C-IMRT，具有统计学差异（P＜0.05）；F-IMRT-OL1肝脏、肾脏的Dmean低于C-IMRT（P＜0.05）；两种计划的脊髓和MU无明显差异（P＞0.05）。结论:对于全段食管癌术后患者的调强放疗计划设计， F-IMRT-OL1计划能在保持靶区剂量充分和剂量均匀性的同时，可以有效地减小肺和心脏剂量的照射体积及平均剂量。

Application of linear accelerator two-degrade collimator in the postoperative treatment of total esophageal carcinoma with intensity-modulated radiotherapy

Objective:To investigate the dosimetric effect of fixing the position of two-degrade collimator in the postoperative treatment of total esophageal carcinoma using intensity-modulated radiotherapy (IMRT).Methods:Thirteen postoperative patients with total esophageal radiotherapy were enrolled to design two reverse IMRT plans.The first plan was two-degrade collimator Jaw Fixed-IMRT (F-IMRT):Based on the upper and lower bounds of the heart,the target area of the F-IMRT plan was divided into three target regions:Upper,middle and lower,which was realized by fixing the collimator.The number and angle of the field were designed for each of the three target segment.The distance between the two target regions for overlap (OL) was 0,1,2,3,4 cm,and five F-IMRT plans (named F-IMRT-OL0.1.2.3.4) were generated.The second plan was conventional-IMRT (C-IMRT):The plan target volume (PTV) was treated as a whole target without fixing the two-degrade collimator.The number and angle of the field was coplanar equal division of 9 fields.The dosimetric difference of PTV and the organs at risk (OARs) and monitor unit (MU) of the two plans were compared.Results:For F-IMRT plan,the two-degrade collimator needed to overlap to ensure the dose coverage of PTV is sufficient,but with the increase of overlap distance,the dose of OARs increased gradually.In this study,F-IMRT-OL1 was the optimal plan.There was no significant difference in conformity index (CI) and homogeneity index (HI) between F-IMRT-OL1 and C-IMRT (P＞0.05).The level of V5 Gy,V10 Gy,V20 Gy and Dmean in lung of F-IMRT-OL1 was lower than those of C-IMRT (P＜0.05),but there was no significant difference in high dose volume of V30 Gy (P＞0.05).The level of V30 Gy,V40 Gy and Dmean of the heart in F-IMRT-OL1 plan was significantly lower than those of C-IMRT (P＜0.05).The level of Dmean of liver and kidney in F-IMRT-OL1 was lower than that in C-IMRT (P＜0.05).There was no significant difference in Dmax of spinal cord and MU between the two plans (P＞0.05).Conclusion:For total esophageal carcinoma postoperative patients,F-IMRT-OL1 is not only dosimetrically feasible as C-IMRT treatment techniques,but also could effectively reduce the irradiation volume of the lung and heart with minimum adverse dosimetric impact on the treatment targets and other OARs.