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Development of heavy ion imaging technology for application in hadron radiotherapy
Published February 24, 2025
The Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST) conducts research to develop advanced measurement and analysis technologies using quantum beams such as X-rays, positrons, and neutrons to contribute to materials development and the realization of a safe and secure society. One of the research themes in this laboratory is the development of alpha-ray imaging technology for advanced heavy ion radiotherapy, in which our ORCA®-Quest qCMOS® camera is used as a detector.
We interviewed Dr. Takeshi Fujiwara, Group Leader of the research group, about the details of the research, the results obtained by using ORCA-Quest, and future research prospects.
Current research
Could you tell us about your research?
Our group is developing dose imaging technology for hadron therapy to improve the accuracy of dose distribution in hadron radiotherapy.
In recent years, hadron radiotherapy using carbon ions has gained attention as an effective treatment method among radiation therapies. Currently, X-rays are primarily used as the radiation source in radiation therapy. However, X-rays have the characteristic of delivering the highest dose at the body's surface, with the dose decreasing as they penetrate deeper into the body where the cancerous tissue is located. This results in the cancerous tissue and the normal tissues at the body's surface being exposed to radiation.
On the other hand, heavy ion beams such as alpha-ray and carbon ions have a characteristic called the Bragg peak, where the dose is low at the body's surface and increases as it approaches the target tissue. This allows for selective irradiation of the cancerous cells without affecting the normal cells at the body's surface. Consequently, various institutions are currently developing carbon ion irradiation technology. To irradiate these heavy ion beams at the target location, it is necessary to measure with high precision the intensity and location of the irradiation and use the results to adjust the source intensity and irradiation location.
However, there are various challenges in the current technology for high precision imaging and measurement of heavy ion beams, and it has not yet been established. Our laboratory is working on developing new imaging technologies to address these challenges.
Dr. Takeshi Fujiwara
Challenges in imaging and measuring heavy particle beams
Conceptual diagram of Glass GEM
Data provided by: Dr. Takeshi Fujiwara, The Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST)
What are the challenges in imaging measurement of heavy particle beams?
Currently, ionization chambers are the primary detectors used for heavy ion beam measurements. However, as point detectors, ionization chambers inherently lack spatial resolution and cannot be used for measuring 2D dose distributions. While array-type ionization chambers have recently been developed, they have limitations: their spatial resolution is only about 5 mm, and they require numerous circuits for multi-channel readout, which not only creates implementation challenges but also increases costs significantly.
To address these limitations, our laboratory is developing a new detector system that combines GEM (Gas Electron Multiplier) technology with high-sensitivity cameras. While GEM was originally developed as a 2D radiation detector that amplifies electrons using gas, our group's Glass GEM achieves higher amplification rates compared to conventional GEMs. Furthermore, by combining it with an Ar/CF4 fluorescent gas mixture, it performs high-sensitivity and high-resolution imaging of heavy ion beams. Using this Glass GEM with Hamamatsu Photonics' ORCA-Quest qCMOS camera, we have achieved heavy ion beam imaging with exceptionally high signal-to-noise ratios and high spatial resolution. Specifically, while detectors using ionization chamber arrays have a spatial resolution of about 5 mm, our detector system using the Glass GEM and camera achieves a spatial resolution of approximately 1 mm.
Results obtained using ORCA-Quest
What results have you seen from using ORCA-Quest?
Before using the ORCA-Quest, we used Hamamatsu Photonics' ORCA-Flash4.0 V3. While this camera, when combined with GEM, could image alpha rays which is a type of particle radiation, the images lacked contrast due to insufficient sensitivity and noise (Imaging example 1).
When we switched to the ORCA-Quest camera, we observed a dramatic improvement in the signal-to-noise ratio compared to the ORCA-Flash4.0 V3. Imaging example 2 shows alpha ray imaging using the ORCA-Quest, where we can not only visualize individual alpha rays as they arrive but also capture subtle variations in dose distribution with high precision. The images clearly show the highest dose concentration at the track endpoints due to the Bragg peak effect. Conventional alpha ray detection methods could only produce integrated images showing faint glowing regions, making it difficult to distinguish between the presence of zero or one alpha particle. Therefore, our system's ability to achieve this level of detection precision while simultaneously performing imaging represents a groundbreaking advancement in the field.
In the future, when this detector is implemented in medical devices and treatment technologies, it will need to meet extremely high precision requirements as it will directly impact human lives. We believe the superior performance of our system will prove invaluable in meeting these demanding requirements.
Glass GEM and camera combined detector
Imaging example
1. Visualized image of alpha radiation using ORCA-Flash4.0 V3.
Data courtesy of: Dr. Takeshi Fujiwara, The Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST).
2. Visualized image of alpha radiation using ORCA-Quest.
Scan mode: Standard scan
Exposure time: 10 ms
Interval: 14.12 ms
Number of pixels used: 1024 (H) × 576 (V)
Data courtesy of: Dr. Takeshi Fujiwara, The Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST).
Prospects for research
Could you tell us about your future research prospects?
Future prospects for heavy ion radiotherapy include the following. We hope to contribute to the advancement of these research and development efforts by using the detector developed by our laboratory.
- 3D heavy ion irradiation using spot scanning
- Development of treatment techniques with fewer side effects using FLASH irradiation
Regarding spot scanning: In conventional heavy ion therapy, the beam is collimated according to the size of the tumor and irradiated. While heavy ion beams offer the advantage of minimal impact on the body's surface tissue, they still pose the challenge of exposing healthy cells around the tumor. To address this issue, a new approach has been proposed: shaping the heavy ion beam into a thin beam called a 'pencil beam' and dynamically scanning it in the X-Y direction to deliver localized treatment. Moreover, by varying the dose, we can adjust the irradiation depth, enabling 3D beam delivery to the tumor.
To verify whether the pencil beam is irradiated at the targeted position in 3D, a detector developed by our laboratory that combines a Glass GEM and a camera is used. This detector can simultaneously and dynamically detect the 2D distribution of the heavy particle beam and the dose intensity, thus accurately determining the 3D dose distribution. We expect that this detector will further develop the spot scanning technique in the future.
Regarding FLASH irradiation: Currently, researchers are developing a treatment method with reduced side effects using "FLASH irradiation." This technique involves delivering an extremely high dose – hundreds of times higher than conventional doses – to the tumor in a very brief moment. Experimental results have shown that compared to prolonged exposure at lower doses, FLASH irradiation maintains therapeutic effectiveness while reducing adverse effects on the human body. While FLASH irradiation requires delivering high doses in very short timeframes, achieving this requires operating synchrotron accelerators in somewhat unconventional ways. Consequently, there remains uncertainty about whether the beam can be delivered at the intended intensity and to the precise target location. We believe our detector can also be valuable in monitoring these parameters.
Researcher profile
Dr. Takeshi Fujiwara
Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST): Group Leader
Mar. 2009
Department of Nuclear Engineering and Management, Graduate School of Engineering, The University of Tokyo, Ph.D.
Apr. 2009
Project Researcher, Department of Nuclear Engineering and Management, Graduate School of Engineering, The University of Tokyo
Apr. 2010
Assistant Professor, Department of Nuclear Professional School, Graduate School of Engineering, The University of Tokyo
Apr. 2015
Research Scientist, Research Institute for Measurement and Analytical Instrumentation, National Institute of Advanced Industrial Science and Technology (AIST)
Oct. 2019
Senior Research Scientist, Research Institute for Measurement and Analytical Instrumentation, National Institute of Advanced Industrial Science and Technology (AIST)
Apr. 2023
Principal Research Scientist, Research Institute for Measurement and Analytical Instrumentation, National Institute of Advanced Industrial Science and Technology (AIST)
Oct. 2023
Principal Research Manager, Research Strategy Planning Division, National Institute of Advanced Industrial Science and Technology (AIST)
Oct. 2024
Group Leader, Advanced Beam Measurement Group, Research Institute for Measurement and Analytical Instrumentation, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST)
Related product
The ORCA-Quest 2 is a new qCMOS® camera, the successor to the ORCA-Quest with further advances such as faster readout speeds in extremely low-noise scan mode and increased sensitivity in the ultraviolet region.
Other case studies
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