Merkel细胞癌电子线放疗中3D打印补偿物的模拟应用

Simulation and application of 3D printed compensator in electron radiation therapy for Merkel cell carcinoma

目的探讨Merkel细胞癌电子线放疗中3D打印补偿物的设计制作过程，验证其在电子线放疗中的可行性。方法CT采集仿真头模图像．在计划系统中模拟Merkel细胞癌的靶区勾画并添加补偿物制定放疗计划。用3D打印机打印补偿物后固定在头模上，再一次CT扫描设计出新治疗计划。对这2个计划选择若干与射束平行的层面，计算对应层面通量图的1通过率。用免洗胶片测量实际剂量分布，计算胶片与计划系统两者剂量通量图的1通过率。打印补偿物的计划与传统的等厚度的补偿物对比，分析靶区的剂量CI、HI值。对两种计划比较行配对t检验。结果3D打印补偿物计划与虚拟补偿物计划的对应层面剂量分布1通过率为（94．7±2．3）％。3D打印补偿物计划中的剂量与扫描胶片的1通过率为96．6％。与传统的补偿物相比靶区CI值明显提高（0．85：0．69，P=0．004），HI值有所改善（1．30：1．26，P=0．011）。结论3D打印电子线补偿物对不同深度肿瘤提供的适形剂量分布可以满足临床需要。

Objective To investigate the design and manufacture of 3D printed compensator in electron radiation therapy for Merkel cell carcinoma, and to verify the feasibility of this technique in electron radiation therapy. Methods Computed tomography was used to collect images of a human head phantom. The delineation of target volume of Merkel cell carcinoma was simulated in the planning system and a radiotherapy plan was formulated after adding the compensator. The compensator was printed out by a 3D printer and fixed on the head phantom. A second CT scan was performed to make a new treatment plan. For the two plans, several planes parallel to the beam were selected to calculate gamma passing rates. The actual dose distribution was measured using disposable films. The gamma passing rate was compared between the film system and the planning system. The conformity index （CI） and the heterogeneity index （HI） of target volume were compared between the plans using the printed compensator and the conventional compensator of the same thickness. Comparison between the two plans was made by paired t test. Results Using the dose distribution of the plan with simulated compensator, the gamma passing rate was 94.7±2. 3% in the plan with 3D printed compensator. Using the dose distribution measured by the film, the gamma passing rate was 96. 6% in the plan with 3D printed compensator. Compared with the conventional compensator, the 3D printed compensator achieved a significantly elevated CI （0. 85 vs. 0. 69, P= 0. 004） and a slightly improved HI （ 1.30 vs. 1.26, P= 0. 001 ）. Conclusions The conformal dose distribution provided by 3D printed compensator for tumors at different depths meets the clinical need.