基于康普顿成像系统的碳离子治疗剂量监测研究

为实现碳离子治疗的精准放疗，精确监测患者体内的三维剂量分布，本文设计一种双层康普顿成像系统和简单反投影算法，利用Geant4仿真软件优化探测系统的结构，评估探测系统的探测效率、成像性能，分析200 MeV/μ的碳离子束轰击有机玻璃（PMMA）靶的三维剂量分布。此外，还使用四对像素1.5 mm×1.5 mm×10.0 mm、12×12阵列型的硅酸钇镥（LYSO）晶体对直径约为3 mm的²²Na点源进行康普顿成像实验，并对影响三维剂量监测精度因素进行分析。结果表明，对于0.847 MeV的γ点源，重建图像在横截面上半高宽（FWHM）增加至2.38 mm、冠状面上扩展至7.02 mm。康普顿成像系统通过探测碳离子束轰击PMMA靶产生的4.439 MeV瞬发γ射线，重建的三维剂量分布与真实三维剂量分布偏差为9.3%。利用LYSO康普顿成像系统样机的²²Na点源成像实验，得到半高宽为4.05 mm的重建图像，验证了康普顿成像方法的实用性。

Compton Imaging System for Dose Monitoring in Carbon-ion Therapy

To obtain accurate radiotherapy for carbon therapy, it is critical to accurately monitor the three-dimensional (3D) dose distribution of patients. This paper designs a double-layer Compton imaging system and a simple back-projection algorithm. Using the Geant4 toolkit, the structure of the Compton imaging system is optimized, the detection efficiency and imaging performance of the Compton imaging system are evaluated, and the 3D dose distribution of 200 MeV/μ carbon ion beam bombarding PMMA target is analyzed. In addition, four pairs of LYSO crystals with 1.5 mm×1.5 mm×10.0 mm and 12×12 pixels were used to perform Compton imaging experiments on a ²²Na point source with a diameter of about 3 mm. Due to the deviation of the reconstructed dose distribution, factors affecting the precision of 3D dose monitoring are also analysed. For the 0.847 MeV γ point source, the reconstructed image has an FWHM increased to 2.38 mm on the cross-section and 7.02 mm on the coronal plane. The compton imaging system detects the 4.439 MeV prompt γ-rays generated by carbon ion beam bombardment of PMMA target, and the deviation of the reconstructed 3D dose distribution from the real 3D dose distribution is 9.3%. Using the ²²Na point source imaging experiment of the LYSO Compton imaging system prototype, a reconstructed image with a FWHM of 4.05 mm was obtained, which verified the practicability of the compton imaging method.