Supporting Material: Proof-of-principle of 3D-printed track-end detectors for dosimetry in proton therapy

Project description and contents of the submitted manuscript: Background: Dosimetric equipment in particle therapy (PT) is associated with high costs. There is a lack of versatile, tissue-equivalent detectors suitable for in-vivo dosimetry. Faraday-cup (FC) type detectors are sensitive to stopped protons, i.e. to trackends. They experience a renaissance in PT as they can cope with high dose rates. Owing to their simple functional principle, production of FC could benefit from the dynamic technological developments in additive manufacturing of sensors. Purpose: To build FC-type detectors for PT by standard 3D-printing. This study seeks to build an integrating, single-channel FC for replacement of a traditional FC and a 2×2 array of FC elements indicating the feasibility of a spatially resolving detector. Methods: Samples of FCs were produced with a dual-extruder 3D-printer with polylactic-acid filaments, which contained graphite in the conductive parts of the detector. Production was optimizied in terms of materials and printing temperature. Samples were characterized by electrical tests and non-destructive 3D x-ray imaging. Beam tests were conducted at a clinical PT machine. Results: Operational FC-type detectors for proton fields were printed. The detected charge of the single-channel FC corresponded qualitatively to the one of a traditional FC. A 2 × 2 FC array was fabricated in a single run. There was a linear relationship between the response of the individual FC elements and the machine output. Conclusions: 3D-printing is a viable method for producing low-cost, tissue-equivalent, FC-type detectors for PT. They could potentially be used as track-end detectors in anthropomorphic phantoms. Shared files: 2x2_FC_matrix: design CAD files of FC array Single_channel_FC: design CAD files of simplified, single-channel FC CT_matrix: high-resolution x-ray CT image set of the 2x2 FC array Measured_values_for_MedPhys_technical_note: Excel sheet of the data presented in the paper投稿稿件的项目说明与内容： 背景：粒子治疗（Particle Therapy, PT）所用的剂量测量设备成本高昂，目前缺乏适用于体内剂量测量（in-vivo dosimetry）的多功能组织等效探测器。法拉第杯（Faraday-cup, FC）型探测器对停止的质子，即质子径迹末端粒子，具有敏感性，且可适配高剂量率射野，因此在粒子治疗领域迎来复兴。鉴于其工作原理简洁，法拉第杯的生产可受益于传感器增材制造（additive manufacturing）领域的快速技术迭代。 研究目的：采用标准3D打印技术制备适用于粒子治疗的法拉第杯型探测器。本研究旨在构建积分式单通道法拉第杯以替代传统法拉第杯，并制备2×2法拉第杯阵列，以验证空间分辨探测器的可行性。 方法：使用双挤出机3D打印机，以掺杂石墨的聚乳酸丝材作为探测器导电部件的原料，制备法拉第杯样品。从材料选型与打印温度两方面优化制备工艺。通过电学测试、非破坏性三维X射线成像对样品进行表征，并在临床粒子治疗设备上开展束流测试。 结果：成功打印出适用于质子射野的法拉第杯型探测器。单通道法拉第杯的探测电荷与传统法拉第杯的定性响应相符。单次打印即可制备2×2法拉第杯阵列，单个法拉第杯单元的响应与治疗机输出呈线性相关。 结论：3D打印是制备低成本、组织等效型粒子治疗用法拉第杯探测器的可行方法，此类探测器有望作为径迹末端探测器应用于拟人化体模中。 共享文件： 2x2_FC_matrix：法拉第杯阵列的CAD设计文件 Single_channel_FC：简化型单通道法拉第杯的CAD设计文件 CT_matrix：2×2法拉第杯阵列的高分辨率X射线CT图像集 Measured_values_for_MedPhys_technical_note：本文所载数据的Excel数据表