自由结构PET在束监测碳离子治疗剂量成像过程研究

In-beam PET 成像为碳离子、质子等粒子放射治疗提供了一种非侵入式的实时剂量监测方法。本文设计自由结构的in-beam PET模型，包括环形、C型、双平板型和直角型PET，并在蒙特卡罗模拟平台GATE上仿真碳离子打靶的in-beam PET成像过程。该PET包含32个探测模块，通过自由组合的方式形成探测视野相近、适用于人体或小动物体不同部位的碳离子治疗剂量成像。每个探测模块由20×20的硅酸钇镥晶体阵列耦合硅光电倍增管构成。单个晶体大小为1.5 mm×1.5 mm×10 mm，像素为1.6 mm。在蒙特卡罗模拟平台GATE中仿真230 MeV/u的碳离子笔形束轰击聚甲基丙烯酸甲酯（PMMA）靶体和在束PET成像过程，得到正电子核素分布后通过MLEM算法得到PET断层图像。结果显示，图像峰位的变化反映了正电子活度峰位的移动，表明自由结构PET可用于在束监测碳离子治疗剂量分布。使用八探头平板型在束PET成像实验和仿真进行对比，其图像一维谱峰值均为27 mm，验证了自由结构PET模型用于在束监测碳离子治疗剂量成像可行。

A Feasibility Study of In-Beam PET Imaging for Dose Verification in Carbon Therapy Using Free PET

In-beam PET imaging provides a noninvasive method to monitor the dose distribution in real-time for particle therapy such as carbon ion therapy and proton therapy. This work designed in-beam PET prototypes based on free PET including cylindrical, open-PET, C-shaped, dual-head plate and rectangular PET scanners and simulated in-beam PET imaging based on these scanners in GATE, a Monte Carlo simulation platform. The scanners were composed of 32 detector modules through free combination and had similar field of view, which could be used for dose monitoring in carbon therapy for the different part of human body and small animal. Each detector module was composed of LYSO array coupled with SiPM. The crystal array contained 20×20 crystals measuring 1.5 mm × 1.5 mm × 10 mm with 1.6 mm pitch. A PMMA phantom was irradiated by the periodic carbon ion pencil beam with an energy of 230 MeV/u and was monitored by the in-beam PET imaging using GATE macros. PET images of the generated positrons were reconstructed by using a MLEM algorithm. Results showed that the shift of image’s peak recreated the variation of positron activity, making it feasible for range verification in the carbon ion therapy by use of free PET scanners. This work compared the reconstructed images between the experimental measurement and simulation based on the dual-head plate scanner containing 8 detector modules. Both peak positions of experimental and simulated images were at 27 mm depth, which validated the feasibility of free PET prototypes for range verification and dose monitoring in carbon ion therapy.