三维适形放射治疗计划评价食管癌根治术后预防性照射野

Three dimensional conformal radiation therapy planning in the evaluation of post-operative prophylactic irradiation fields for esophageal carcinoma

目的 应用三维适形放射治疗计划评价食管癌根治性切除术后预防性照射野的剂量分布。方法 38例食管癌切除后均行放射治疗前CT扫描、三维重建 ,模拟设计前后垂直照射野及两侧水平野 ,每例均设两种照射方式即 3个野 (前、左、右 )和 4个野 (前、后、左、右 ) ,照射野长度分别为 2 2、18cm ,宽度分别为 7、6cm。在两种照射方式中根据每个野剂量权重不同再分组 ,比较不同组间食管床靶区最大剂量、平均剂量、最小剂量的平均值以及脊髓接受的最大剂量、平均剂量及其剂量体积的平均值 ,同时观察两肺V2 0 、V15大小。结果 当照射野长度增大时 ,靶区剂量的不均匀性增加 ,脊髓剂量也增加。照射野长度相同时 ,食管床靶区剂量分布的均匀性 4个野照射优于 3个野照射 ,而脊髓剂量的增加并不明显 ,两肺V2 0 、V15在 4个野或 3个野照射时无明显差别。结论 食管癌根治术后预防性照射以 4个野照射方式较好。当处方剂量 5 0Gy时 ,以前后两野对穿剂量权重为 18和 16Gy或 18和 18Gy、两侧水平野剂量权重为 8和 8Gy或 7和 7Gy的剂量分布最合适。

ObjectiveEvaluation of the dose distribution in esophageal bed region was carried out with prophylactic irradiation fields after esophagectomy by three dimensional conformal radiation therapy planning .MethodsFrom 2001 to 2003, 38 esophageal cancer patients who had received radical esophagectomy were given chest CT scanning and reconstruction of organs and contours by the three-dimensional conformal treatment planning system. Design of the anterior,posterior vertical and double horizontal lateral fields was made. For each patient,double pattern irradiation was adopted as three(Anterior,Left,Right) or four(A,P,L,R) fields. The field sizes were 7 cm×22 cm and 6 cm×22 cm or 7 cm×18 cm and 6 cm×18 cm .According to dose weight of each field in the irradiated field of the same length ,these patients were again divided into eight groups to compare the mean value of maximum dose,minimum dose and mean dose in the esophageal bed target and also to compare the maximum dose ,mean dose and the mean value of dose volume on the spinal cord and ,simultaneously,the V 20 ,V 15 of bilateral lungs in the different groups. Results When the length of the field increased,the uniformity of dose distribution in the esophageal bed target became poor,with the mean value of maximum dose in the spinal cord also increased. The dose distribution of four irradiation fields was better than of three fields,with inconspicuous increase in the mean value of maximum dose of spinal cord. However there was insignificant difference in V 20 ,V 15 no matter four or three fields were used. Conclusion We recommend that four irradiation fields be used rather than three fields for esophageal carcinoma postoperative prophylactic irradiation. For prescription dose of 50 Gy,the dose weight in each field should be 18,16 Gy or 18,18 Gy for anterior and posterior fields;8,8 Gy or 7,7 Gy for double horizontal lateral fields.