A scintillating fibre based beam profile monitor for ion therapy beams

该项目是与海德堡离子束治疗诊所（HIT）讨论的结果，旨在进一步开发和研究用于离子治疗诊所或其他加速器设施的射束轮廓监测器。在HIT质子，氦，碳和氧离子束可以在20 cm × 20 cm的区域内扫描，具有多种能量和强度设置，用于患者治疗。跟踪系统在线监测束流位置并提供反馈。所提出的探测器基于0.25 mm的塑料反射纤维，该纤维粘合成带，光电二极管阵列读出（0.8 mm通道）提供来自每个探测器平面的一维轮廓信息。当前系统是具有2 mm通道间距和4-8 kHz读出的商业多丝比例腔室（MWPC）。气体电离产生的离子的漂移时间约为150 µs，并产生死区时间。MWPC将很快达到其使用寿命，需要更快，更精确的系统来替代它。更快的读出速率（~ 10 kHz）将允许更高的剂量率和更快的患者治疗时间。具有光电二极管阵列的光纤检测器由于其速度和通道尺寸，本质上应该比当前系统更好地执行。初步开发始于使用可用材料和电子设备的概念验证探测器，以确定项目的可行性。现有的5层光纤带用于小型检测器中，该小型检测器具有一个64通道光电二极管，该光电二极管以期望的信号积分周期（100微秒）读出，但由于可用的电子器件而仅以1 kHz采样。结果是积极的，并已发表在JINST（https：//doi.org/10.1088/1748-0221/13/05/P05030）。下一阶段（正在进行中）试图实现离子治疗束监测器所需的所有规格。它由使用第一个版本的定制电子器件的最终探测器的2/5（按面积）组成，并使用前2层光纤带（以最大限度地减少光束中的材料），使用两种不同类型的闪烁体。未处理的数据以10 kHz的目标读出速率输出用于离线分析。用相当于半年剂量的辐照对两条光纤带进行了辐照，以研究辐射损伤效应。详细研究了塑料纤维对不同离子类型和能量的响应。正在研究用其他离子进行测试的其他设施。第二阶段（未来）将涉及除了离线输出全尺寸原型之外的机载处理的开发。此外，还将开发更轻的纤维垫。第二阶段的成功将导致知识和技术转移到HIT，以便在医疗环境中进一步开发和使用。预计将雇用一名博士研究员开发新的探测器、处理算法和探测器模拟，并与主要研究人员和电子开发人员一起分析收集的数据。

This project has been developed as a result of discussions with the Heidelberg Ion-beam Therapy Clinic (HIT) and aims to further develop and study a beam profile monitor for use at ion therapy clinics or other accelerator facilities. At HIT protons, helium, carbon, and oxygen ion beams can be scanned over a 20 cm by 20 cm area with multiple energy and intensity settings for patient treatment. The tracking system monitors the beam position online and provides feedback.The proposed detector is based on 0.25 mm plastic scintillating fibres bonded as a ribbon with photodiode array readout (0.8 mm channels) providing 1-dimensional profile information from each detector plane. The current system is a commercial Multi-Wire Proportional Chambers (MWPC) with 2 mm channel pitch and 4-8 kHz readout. Ions from gas ionisation have drift times of ~150 µs and create a dead time. The MWPC will reach their life span soon and a faster, more precise system is desired for its replacement. A faster readout rate (~10kHz), would allow for higher dose rates and faster patient treatment times. A fibre detector with photodiode arrays should perform intrinsically better than the current system due to their speed and channel size. Preliminary development began with a proof-of-concept detector using available materials and electronics to determine the feasibility of the project. An existing 5-layer fibre ribbon was used in a small detector with one 64 ch photodiode read out with a desired signal integration period (100 microseconds) but only sampled at 1 kHz due to the available electronics. The results were positive and have been published in JINST (https://doi.org/10.1088/1748-0221/13/05/P05030).The next phase (in progress) attempts to achieve all the specifications required for an ion therapy beam monitor. It consist of 2/5 of the final detector (by area) using the first version of custom electronics, and uses the first 2-layer fibre ribbons (to minimise the material in the beam) using two different types of scintillator. The unprocessed data is output for offline analysis at the target readout rate of 10 kHz. Two fibre ribbons have been irradiated with the equivalent of half a year of dose to study radiation damage effects. The response of plastic scintillating fibre to different ion types and energies is studied in detail. Other facilities for testing with other ions are being investigated. The 2nd phase (future) would involve development of on-board processing in addition to offline output of a full size prototype. Additionally, lighter fibre mats would be developed. A successful 2nd phase would lead to transferring the knowledge and technology to HIT for further development and use in a medical environment. The hiring of a doctoral researcher is foreseen to develop the new detectors, processing algorithms, and detector simulations, and analyse the data collected together with the primary investigator and electronics developer.