基于锥形束CT图像的肿瘤放疗计划剂量计算可行性分析

随机选取40例(头颈部组、胸部组、腹部组、盆腔组各10例)不同部位的Rapid Arc病例,首先导出所有病例首次治疗时位置验证产生的锥形束电子计算机断层扫描(Cone-beam computed tomography,CBCT)原始投影文件,用自行开发的锥形束CT图像处理工具(Cone-beam CT imaging toolkit,CITK)对CBCT投影进行散射校准并三维重建为0.5 cm层厚的断层CBCT图像;然后用Eclipse软件将计划CT图像与该病例对应的CBCT图像进行配准并将计划CT上勾画的靶区等结构映射到CBCT图像上保存;接着用相同的处方剂量和优化条件设计放疗计划,采用各自的HU-ED标定曲线进行剂量计算后生成剂量体积直方图(Dose volume histogram,DVH)并导出;最后计算所有DVH的剂量分布指数(Dose distribution index,DDI)值,用配对t检验分析两种方法的结果是否存在差异。结果显示,4组病例中只有胸部组病例有统计学差异(t=2.284,p0.05),其余组病例均无统计学差异(p0.05)。实验结果提示,在对CBCT图像进行有效的散射校准并标定对应的HU-ED曲线后,其可用于肿瘤放疗计划的剂量计算。

Feasibility analysis of dose calculation for tumor radiotherapy planning based on cone-beam computed tomography images

Forty cases undergoing RapidArc treatment were selected and grouped equally into head neck group, chest group, abdominal group, and pelvic cavity group. The raw cone-beam computed tomography(CBCT) projections produced in position verification were exported and then scatter-corrected by a self-developed cone-beam CT imaging toolkit (CITK) tool and reconstructed to be 5 mm thick tomographic files, which were then matched with the planning CT to map out the target area by eclipse with all the contour line saved. The radiotherapy of the planning CT and modified CBCT was designed with the same prescription dose, and the optimized conditions, and dose volume histogram (DVH) diagrams were generated and exported through dose calculation by Hounsfield unit-electron density (HU-ED) calibration curves. Finally, the dose distribution index (DDI) values for forty tumor patients were calculated and at-test was used in the quantitative analysis to discuss whether statistics differences existed between the two methods. Statistical differences between the two methods in the four groups were found in the chest group (t=2.284,p<0.05), while no statistical differences existed (p>0.05) in all the other measurements. The comparative analysis showed that the effectively-corrected CBCT image and the corresponding calibrated HU-ED curves can be used in the dose calculation of tumor radiotherapy planning.