[Paper Review] A Prototype Scintillator Real-Time Beam Monitor for Ultra-high Dose Rate Radiotherapy

Daniel Levin, Peter S. Friedman+6 more|arXiv (Cornell University)|May 24, 2023

Radiation Detection and Scintillator Technologies36 references5 citations

TL;DR

This paper presents a prototype scintillator-based real-time beam monitor (FBSM) for ultra-high dose rate (FLASH) radiotherapy, utilizing a novel inorganic hybrid scintillator to enable large-area, low-mass, radiation-tolerant beam monitoring with linear response and sub-microsecond real-time data processing. The device demonstrated stable signal output after 212 kGy cumulative dose at 234 Gy/s, high-resolution 2D beam imaging, and IEC-compliant beam-interrupt capability in FLASH and conventional electron beams.

ABSTRACT

FLASH Radiotherapy (RT) is a potentially new cancer radiotherapy technique where an entire therapeutic dose is delivered in about 0.1 s and at ~1000 times higher dose rate than in conventional RT. For clinical trials to be conducted safely, precise and fast beam monitoring that can generate an out-of-tolerance beam interrupt is required. A FLASH Beam Scintillator Monitor (FBSM) is being developed based in part on a novel proprietary inorganic hybrid scintillator material. The FBSM provides large area coverage, low mass profile, linear response over a broad dynamic range, radiation tolerance, and real-time analysis IEC-compliant fast beam-interrupt signal. This paper includes the design concept and test results from a prototype device in radiation beams that include heavy ions, FLASH level dose per pulse electron beams, anda hospital radiotherapy clinic with electron beams. Results include image quality, response linearity, radiation hardness, spatial resolution, and real-time data processing. The scintillator showed a small -0.02%/kGy signal decrease after a 212 kGy cumulative dose resulting from continuous exposure for 15 minutes at a FLASH compatible dose rate of 234 Gy/s. These tests established the linear response of the FBSM with respect to dose per pulse. Comparison with commercial Gafchromic film indicates that the FBSM produces a high resolution 2D beam image and can reproduce a nearly identical beam profile. At 20 kfps or 50 microsec/frame, the real-time FPGA based computation and analysis of beam position, beam shape, and beam dose takes < 1 microsec.

Motivation & Objective

• To develop a real-time, high-speed beam monitor for ultra-high dose rate (FLASH) radiotherapy to ensure safety and precision in clinical trials.
• To address the lack of reliable, fast-responding beam monitoring systems capable of generating IEC-compliant beam-interrupt signals in FLASH therapy.
• To evaluate the performance of a novel inorganic hybrid scintillator in high-dose-rate environments for beam position, shape, and dose monitoring.
• To achieve real-time data processing with sub-microsecond latency for beam parameters using FPGA-based computation.
• To validate the monitor’s linearity, spatial resolution, and radiation hardness across FLASH electron beams, heavy ions, and clinical electron beams.

Proposed method

• The FBSM employs a proprietary inorganic hybrid scintillator material with high radiation tolerance and fast decay time for real-time beam detection.
• A high-speed CMOS camera captures scintillation light at 20 kfps (50 μs/frame) to enable real-time beam imaging and parameter extraction.
• An FPGA-based processing system computes beam position, shape, and dose in less than 1 μs per frame to meet IEC safety standards for beam interruption.
• The system was tested in three beam environments: FLASH-level electron beams (234 Gy/s), heavy ion beams, and a hospital-based electron therapy unit.
• Beam profiles were compared to Gafchromic film for validation of spatial resolution and image fidelity.
• Radiation hardness was assessed by exposing the scintillator to 212 kGy cumulative dose over 15 minutes at 234 Gy/s, measuring signal stability.

Experimental results

Research questions

• RQ1 Can a scintillator-based beam monitor achieve real-time, sub-microsecond response for beam-interrupt functionality in FLASH radiotherapy?
• RQ2 Does the novel inorganic hybrid scintillator maintain linear response and signal stability under ultra-high dose rate irradiation (234 Gy/s) over extended exposure?
• RQ3 How does the spatial resolution and beam profile accuracy of the FBSM compare to established reference dosimeters like Gafchromic film?
• RQ4 Can the FBSM reliably detect beam position, shape, and dose in diverse beam types, including FLASH electron beams, heavy ions, and clinical electron beams?
• RQ5 What is the radiation-induced signal degradation of the scintillator after cumulative exposure to 212 kGy at FLASH dose rates?

Key findings

• The FBSM achieved real-time beam data processing with a latency of less than 1 μs per frame at 20 kfps, meeting IEC requirements for fast beam-interrupt functionality.
• The scintillator exhibited a signal decrease of only -0.02%/kGy after 212 kGy cumulative dose at 234 Gy/s, indicating high radiation tolerance.
• The beam profile measured by the FBSM closely matched that of Gafchromic film, confirming high spatial resolution and image fidelity.
• The FBSM demonstrated linear response to dose per pulse across all tested beam conditions, including FLASH electron beams and heavy ions.
• The system successfully generated accurate, real-time beam position, shape, and dose information in both clinical and FLASH-level beam environments.
• The prototype achieved large-area beam coverage with a low-mass profile, suitable for integration into clinical radiotherapy systems.