Speaker
Description
Innovative Light Detection System for Rapid 3D Radiation Dose Monitoring
B. Mindur on behalf of Dose3D Future, AGH University of Krakow, Poland
Introduction
According to the World Health Organization (WHO), cancer remains one of the leading causes of death worldwide. Radiotherapy is often the primary or sole therapeutic approach used in treatment. Ensuring that each patient receives fast, efficient, and safe treatment is essential. To address this need, our team has developed a scalable detection system that utilizes 3D-printed plastic scintillators as active elements for evaluating the therapeutic dose distribution in spatially reconfigurable detectors (phantoms). Such a phantom could be used to cross-check and validate the simulation results during the preparation of photon radiotherapy treatment plans. The system’s reconfigurability allows for adaptation of the phantom’s geometry. Thanks to 3D printing, individual scintillation voxels can be connected in nearly any configuration, enabling a customized measurement setup tailored to specific requirements. The phantom is designed to replicate the affected tissue area and its surroundings, ensuring precise dosimetric assessment. Each scintillator is connected to the readout electronics via an optical fiber, allowing the generated photons to be transmitted outside the phantom’s active region. The system’s hardware has been designed with modularity and scalability, making it suitable for both small- and large-scale detection systems across various applications.
Key Features of the System
From a hardware perspective, the system's modularity is evident in its fundamental building blocks, referred to as slices. A single slice comprises a set of printed circuit boards (PCBs) and components connected, capable of reading out visible light from 64 channels. Each slice consists of a baseboard (BB), a front-end board (FEB) with a Maroc-3A application-specific integrated circuit (ASIC), a high-voltage power supply board (HVB), a calibration board (CALB), and a multichannel photomultiplier tube (PMT). Additionally, a timing board (TIMEB) ensures system-wide time synchronization.
The BB serves as the central hub for data communication and signal interconnection between the FEB, the programming and debugging interface, a Gigabit Ethernet interface for PC communication, and power distribution. It also hosts the Mars-3A mini module, which is equipped with an AMD Artix 7 field-programmable gate array (FPGA). The compact FEB has been designed to interface the ASIC and the PMT assembly with the FPGA module, HV power supply board, and the CALB. The Maroc-3A ASIC processes and measures signals from the multichannel PMT, providing event detection and charge measurement capabilities. For this project, the Hamamatsu H7546B 64-channel PMT was selected due to its sensitivity to visible light, with peak sensitivity around 420 nm, closely matching the scintillator’s emission spectrum.
Due to space constraints on the FEB, the HVB was designed as a separate PCB, providing isolation between the high-voltage unit and the rest of the system. This modular design also enables the independent replacement of faulty components, significantly reducing maintenance and repair costs. The CALB is responsible for providing precise calibration signals to the Maroc-3A ASIC and includes monitoring headers and pins for extended diagnostics. All boards—BB, FEB, HVB, and CALB—are stacked together to form a single slice, also providing mechanical support for the 3D-printed PMT handler components and the PMT itself.
The TIMEB ensures synchronization across the system by generating a reference clock and reset signals for all slices. A 19-inch crate serves as a key component of the data acquisition (DAQ) infrastructure, designed to house up to eight slices along with the TIMEB in a well-organized manner. The DAQ system can be easily expanded by adding more slices to additional crates, thereby increasing the number of available readout channels.
Results
Key hardware parameters of the system, such as trigger threshold linearity, analog signal amplification gain and offset, and timing characteristics, have been measured, providing detailed insights into critical system performance. These evaluations include electronic tests using a pulse generator as well as laser light pulses to simulate realistic operational conditions. Laser pulse testing enables a detailed characterization of the PMT’s optical properties, including spectral response and optical crosstalk, both of which play a significant role in test-beam measurements. A dedicated analysis confirms that the PMT’s individual channel response remains highly uniform across the photocathode surface, with only minor fluctuations of approximately 5%. Tests using plastic scintillators have also been conducted. Amplitude spectra obtained from these tests confirm that the system is capable of detecting single-photoelectron signals generated by weak scintillation light.
With a fully functional detection system and a set of dedicated phantoms, a series of carefully planned test measurements have been performed. Test-beam sessions have been conducted at the Maria Sklodowska-Curie National Research Institute of Oncology in Kraków. The treatment center is equipped with a Varian TrueBeam flat-field X-ray generator, which was used in all test-beam campaigns to validate the system’s performance under realistic irradiation conditions using an actual therapeutic photon beam. Preliminary results of reconstructed dose values compared to the treatment calibration dose profiles are very promising.
Conference Presentation
At the conference, we will present the complete prototype system, including dedicated hardware, firmware, and software, as well as a set of configurable phantoms made from tissue-equivalent, 3D-printed plastic scintillator cubes. Key design features, such as system modularity, scalability, and potential applications, will be highlighted. Additionally, we will demonstrate the flexibility of the phantom, which can be customized into nearly any arbitrary 3D arrangement, and share results from test-beam campaigns conducted using a clinical linear accelerator at a cancer treatment facility. Preliminary results of actual dose reconstruction compared to the treatment calibration dose profiles will also be presented, along with details of measurement procedures. Our presentation will focus on recent results that have not been previously shared.
References
[1] B. Mindur, et al., System for radiation dose distribution monitoring in radiotherapy treatment planning, Nuclear Instruments and Methods in Physics A 1069 (2024) 169834.
[2] https://dose3d-future.fis.agh.edu.pl/
| Workshop topics | Applications |
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