螺旋断层放疗图像引导技术在鼻咽癌精确放疗中的应用

目的：探讨螺旋断层放射治疗系统图像引导技术在鼻咽癌精确放疗中的应用。方法：选择本院螺旋断层放疗中心2013年5月至2013年7月30例接受螺旋断层放疗的鼻咽癌患者,每例患者在每次治疗前均采用兆伏级CT（ MVCT）扫描获得治疗体位图像,将该图像与定位CT图像进行配准,分别获得X轴（左右方向）、Y轴（头脚方向）、Z轴（腹背方向）3个方向的偏移数据,并根据van-Herk推荐外扩边界估计值公式计算得出靶区外扩边界的估计值。使用该估计值进行边界外扩,重新勾画靶区,在计划系统中重新计算剂量,得到调整前后的正常组织平均剂量对比。结果：30例鼻咽癌患者的摆位误差（系统误差±随机误差）在X、Y、Z方向上分别为（0.96±0.88）mm、（1.55±1.13）mm、（1.03±0.78）mm,根据van-Herk推荐外扩边界估计值公式计算得出：X方向为1.74 mm, Y方向2.14 mm,Z方向1.65 mm。使用不同外扩边界值前后,腮腺、内耳、颞颌关节、喉（食道）、下颌骨的平均剂量降低比例分别为12％、9.5％、11.9％、14.7％、22.4％。结论：TomoTherapy图像引导技术保证了精确放疗的实施,降低了正常组织的平均照射剂量,可为临床医生勾画靶区提供依据。

Application of image-guided radiation therapy by helical tomotherapy in the precise radiotherapy for nasopharynx carcinoma

Objective：To investigate the application of the image-guided radiation therapy by Helical Tomotherapy in the precise radiotherapy for Nasopharynx Carcinoma. Methods： 30 patients with nasopharynx carcinoma accepted Helical Tomotherapy from May 2013 to July 2013 in the Tomotherapy Center of our hospital were selected. And before each treatment, the position image screened by Tomotherapy megavoltage CT （ MVCT） of each patient was collected for registration of positioning CT image. The coefficient of correlation along all three directions on lateral （X）, longitudinal （Y）, vertical （Z） were collected respectively. The estimated value of expanded boundary was calculated by the recommended van-Herk formula. Using the estimated value for boundary expansion, target section was re-delineated, and the dose was re-calculated in the planning system. The average dose of normal tissue was compared between pre-adjustment and post-adjustment. Results： The coefficient of correlation of 30 patients with nasopharynx carcinoma on X, Y and Z direction was （0.96±0.88） mm, （1.55±1. 13） mm and （ 1. 03 ± 0. 78 ） mm respectively, which represented （ system error data ± random error data ） . According to the calculation of van-Herk recommended formula on the estimated value of expanded boundary, X direction was 1. 74 mm, Y direction was 2. 14 mm and Z direction was 1. 65 mm. The reduced proportion of average dose to parotid gland, inner ear, temporomandibular joint, throat （ esophagus） , and mandible was 12%, 9. 5%, 11. 9%, 14. 7%, 22. 4% respectively after using the new external expansion boundary values. Conclusions： The image-guided radiation therapy by Helical Tomotherapy ensures the precise treatment for Nasopharnx Carcinoma, reduces the radiation dose of normal tissue, and provides the evidence of target section for clinicians.