不同照射野调强放疗在胸中下段食管癌中对正常组织受量的影响

Normal Tissue Dose Affected by IMRT with Different Radiation Fields for Middle and Lower Esophageal Cancer

目的比较三种不同放疗布野方式在胸中下段食管癌患者中的剂量分布情况,为临床调强放疗计划的选择提供参考。方法选择30例胸中下段食管癌患者进行CT定位,并由主治医师画出各自靶区,然后设计GTV和PTV,并设计三组布野方案(A组:0°、72°、144°、216°、288°;B组:0°、57°、144°、216°、303°;C组:0°、42°、144°、216°、318°),分别模拟三维适型调强计划,给予相同的单次剂量、治疗次数及优化条件,最后以95%PTV体积获得60 Gy处方剂量进行归一,利用等剂量曲线以及剂量体积直方图对以上三组计划进行下列参数的两两比较:心脏受量为20 Gy、30 Gy、40 Gy、50 Gy时的体积值;左右侧肺分别受量为5 Gy、10 Gy、20 Gy、25 Gy、30 Gy、35 Gy、40 Gy时的体积值;脊髓最大点受量。结果 C组与A、B组相比,患者肺低剂量受照射体积(V5、V10)明显减小(P≤0.003),C组V20较A组有提高,高剂量受照射体积V25、V30及V35较A、B两组有一定的提高(P<0.05),但均在临床可评价的安全范围内;脊髓最高点及心脏受量比较提示:C组脊髓最大点受量较A组增加,C组心脏V20较其他两组有增加(P<0.05),但也均在临床可评价的安全范围内。结论三维适型调强计划中,在5野均分的基础上适当减小两前斜野与零度野之间的夹角(C组),可以在基本不增加心脏和脊髓受量的同时有效地减少肺低剂量区受照射体积,但有提高肺高剂量区受照射体积的风险。

Objective To compare the dose distribution of 3 different radiation fields in patients with middle and lower esophageal cancer. Methods 30 cases received CT location and then GTV and PTV were designed with 3 different radiation fields： Group A （0°, 72°, 144°, 216° and 288°）, Group B （0°, 57°, 144°, 216° and 303°） and Group C （0°, 42°, 144°, 216° and 318°）; with the same amount of single dose, the same times of treatment and the same optimum condition, the 60 Gy prescription dose was normalized by 95% of PTV volume; the isodose curve and dose volume histogram were applied in the multiple comparison of the following parameters of the 3 groups： the volume of heart when given 20 Gy, 30 Gy, 40 Gy and 50 Gy, the velum of the left lung and that of the right when given 5 Gy, 10 Gy, 20 Gy, 25 Gy, 30 Gy, 35 Gy and 40 Gy, and the maximum dose of spinal cord. Results The volumes of lungs irradiated by low dose （V5 and V10） in patients of Group C decreased obviously （P〈0.003） and its volume by dose V20 was bigger than that in patients of Group A; the volumes of lungs increased when irradiated by high dose （V25, V30, and V35） in patients of Group C, more than those in patients of Group A and Group B （P〈0.05）, but they were still in the safe range of clinical evaluation; the maximum dose of spinal cord in patients of Group C was higher than that in patients of Group A while its volume of heart under V20 was bigger than those of patients in the other two groups （P〈0.05）, and as well, they were still in the safe range of clinical evaluation. Conclusions The radiation field of Group C can effectively reduce the volume of lung irradiated by low dose without increasing the dose in heart and spinal cord, howev- er, it has the risk of increasing the volume of lung by high dose.