[Paper Review] The SiFi-CC detector for beam range monitoring in proton therapy -- characterization of components and a prototype detector module

Katarzyna Rusiecka|arXiv (Cornell University)|Jun 19, 2023

Radiation Detection and Scintillator TechnologiesPhysics and Astronomy3 citations

TL;DR

This paper presents the design, component optimization, and prototype testing of the SiFi-CC detector for real-time proton beam range monitoring in proton therapy. Utilizing inorganic scintillating fibers and silicon photomultipliers (SiPMs), the study evaluates light propagation via ELA and ELAR models, achieving a position resolution of 33.38 mm and energy resolution of 7.73% with the Philips DPC3200-22-44 SiPM and Hyperion DAQ system—demonstrating feasibility for clinical range verification.

ABSTRACT

The following thesis presents research which constitutes the first steps towards the construction of a novel SiFi-CC detector intended for real-time monitoring of proton therapy. The detector construction will be based on inorganic scintillating fibers and silicon photomultipliers. The scope of the presented thesis includes the design optimization of the components of the proposed detector, as well as the construction, characterization, and tests of a prototype. The design optimization comprised an extensive systematic comparison of chosen inorganic scintillating materials, different types of scintillator surface modifications (wrappings and coatings), and different types of interface materials ensuring optical contact between the scintillators and the photodetector. The propagation of scintillating light in all investigated samples was described using two models: the exponential light attenuation model (ELA), and the exponential light attenuation model with light reflection (ELAR). The two models yielded the corresponding methods for energy and position reconstruction. Furthermore, the samples were investigated for energy and position resolution, light collection, and timing properties. Based on the results obtained from the optimization study, the detector prototype was constructed. Prototype tests were performed with two different photodetectors and data acquisition systems. The performance of the prototype was evaluated using the same metrics as in the case of single-fiber measurements. The best results were obtained in measurements with Philips Digital Photon Counting photosensor and the Hyperion platform, yielding a position resolution of 33.38 mm and an energy resolution of 7.73 %. The results obtained are satisfactory and sufficient for the successful operation of the proposed SiFi-CC detector.

Motivation & Objective

• To develop a real-time beam range monitoring system for proton therapy using novel scintillating fiber and SiPM technology.
• To optimize scintillator materials, surface treatments (wrappings/coatings), and optical interface materials for maximum light collection and signal fidelity.
• To evaluate and compare the performance of different photodetectors and data acquisition systems on a prototype detector module.
• To validate the ELA and ELAR models for energy and position reconstruction using experimental data from single-fiber and prototype measurements.
• To demonstrate that the optimized SiFi-CC detector prototype achieves sufficient resolution for clinical beam range verification.

Proposed method

• Systematic comparison of inorganic scintillating materials (e.g., LSO, LuYAP) with varying surface treatments (wrappings, coatings) and optical interface materials (e.g., RTV silicone, index-matching gels).
• Application of the Exponential Light Attenuation (ELA) and ELA with Reflection (ELAR) models to describe light propagation and enable energy and position reconstruction.
• Measurement of energy resolution, position resolution, light collection efficiency, and timing properties using calibrated gamma sources and proton beams.
• Construction of a prototype detector module using a 2D array of scintillating fibers coupled to SiPMs, tested with two photodetectors: Philips DPC3200-22-44 and Hamamatsu MPPC.
• Use of the Hyperion data acquisition platform and SiFiDetectorAnalysis framework for signal processing and event reconstruction.
• Employment of gradient tree boosting algorithms for position reconstruction in prototype data, informed by single-fiber calibration.

Experimental results

Research questions

• RQ1 Which scintillating material and surface treatment combination maximizes light collection efficiency and signal-to-noise ratio in proton beam monitoring?
• RQ2 How do different optical interface materials affect the light transmission and position resolution in fiber-based scintillator detectors?
• RQ3 To what extent do the ELA and ELAR models accurately reconstruct energy deposition and interaction position in scintillating fibers?
• RQ4 What is the achievable energy and position resolution of a prototype SiFi-CC detector module using state-of-the-art SiPMs and data acquisition systems?
• RQ5 Can the optimized SiFi-CC detector prototype achieve resolution performance suitable for real-time proton beam range verification in clinical settings?

Key findings

• The Philips DPC3200-22-44 digital SiPM paired with the Hyperion DAQ platform delivered the best performance, achieving a position resolution of 33.38 mm.
• The energy resolution of 7.73% was achieved with the same configuration, indicating sufficient sensitivity for proton range verification.
• The ELAR model, which accounts for light reflection at fiber boundaries, provided improved position reconstruction accuracy compared to the standard ELA model.
• Surface treatments such as reflective coatings and optimized wrapping materials significantly enhanced light collection efficiency, reducing signal loss.
• The prototype detector demonstrated stable and repeatable performance across multiple measurement campaigns with consistent resolution metrics.
• The study confirmed that the SiFi-CC detector concept is viable for real-time beam range monitoring, with performance metrics meeting the threshold for clinical applicability.