Rapid Visualization of "Radiochemical Assessment" in Alpha-Targeted Radiopharmaceuticals – Commercial Launch of a System for Simultaneous Analysis of Chemical Form and Radioactivity of Alpha-Emitting Nuclides – 

2025.05.14

The Nuclear Science and Engineering Centre (NSEC), in collaboration with the National Institutes for Quantum Science and Technology (QST), developed a rapid and simultaneous analysis system for determining the chemical form and radioactivity of alpha-emitting radionuclides used in targeted alpha therapy (TAT). In April 2025, the system was commercialized as “NuS-Alpha” by Meisho Co., Ltd.

TAT has recently attracted significant attention as a promising cancer treatment. It uses alpha particles to precisely target tumor cells while minimizing damage to surrounding healthy tissues. To ensure the therapeutic efficacy of radiopharmaceuticals ― such as astatine-211 (211At) and actinium-225 (225Ac), it is essential to accurately evaluate both their chemical forms and radioactivity before administration.

Here, analytical techniques must be not only highly accurate but also extremely rapid due to a short half-life of 211At, approximately seven hours. However, Conventional methods have several difficulties:
(1) X-ray interference prevents the analysis of certain chemical forms.
(2) Analytical procedures are often complex and time-consuming,
(3) Chemical form and radioactivity must be measured separately.
(4) Multiple instruments require large physical space, resulting in increased movement of personnel and equipment, which raises the risk of radiation exposure.

To overcome them, NSEC and QST developed an analysis system combining thin-layer chromatography (TLC), an alpha-sensitive scintillator, and a high-sensitivity CCD/CMOS camera. In this system, TLC is used to separate 211At chemical forms based on their chemical properties and the alpha particles are visualized using the scintillator, thereby enabling real-time and simultaneous analysis of both the chemical form and radioactivity within a single device.

As a result, the system can accurately distinguish chemical forms that previously could not be individually identified due to X-ray interference and provide a clear “visualization” of the effectiveness of the radiopharmaceuticals.　Moreover, by achieving an approximately 200-fold improvement in sensitivity, the system reduces the analysis time to approximately one-fortieth of that required by conventional methods, thereby preventing unnecessary loss of valuable radiopharmaceuticals. The ability to simultaneously analyze chemical form and radioactivity in real time also significantly streamlines the workflow and contributes to reducing radiation exposure risks for operators. Additionally, its compact space-saving design allows for easy implementation even in limited spaces such as clinical facilities and research laboratories.

NuS-Alpha, which enables accurate, rapid, simple, and space-efficient analysis, is expected not only to contribute significantly to the clinical implementation of TAT but also to find broad applications in other radiation-based therapies and environmental monitoring.

JAEA HP Press release (Japanese only)

Approaching the latest cancer treatment from chemical changes of water molecules after exposure to ionizing radiation – Successfully developed a calculation program that visually tracks the dynamics of water molecules by radiolysis – 

2025.05.08

Based on the latest scientific knowledge of radiation physics and chemistry, to clarify the cancer-killing mechanisms of the latest radiation therapy, the Nuclear Science and Engineering Center (NSEC) has successfully developed and released a calculation program that tracks and visualizes the behavior of chemical products by water radiolysis in the human body.

When a living body is irradiated in radiotherapy, physical interactions between the molecules and radiation are induced. Subsequently, water radiolysis occurs and generates a large amount of various kinds of chemical products, such as OH radicals and hydrated electrons. These products cause chemical reactions with DNA. In recent years, "FLASH radiotherapy" has appeared, which instantaneously irradiates a large amount of radiation, efficiently eradicating tumors while suppressing side effects in normal tissues. For such reasons, FLASH radiotherapy has attracted worldwide attention. However, the induction mechanisms of suppressed side effects are unclear, and a hypothesis that the chemical products in the human body are of importance has been made. To date, various chemical codes that simulate the behavior of water-radiolysis products have been developed by researchers worldwide. However, there are limitations on radiation types that can be handled in the code.

In this study, using the PHITS code, we developed a chemical code (hereinafter referred to as "PHITS-Chem") that enables the simulation of water radiolysis and the dynamics of the chemical products for diverse types of radiations used in cancer treatment. By combining PHITS-Chem with the 3D visualization application PHIG-3D, which is dedicated to the PHITS code, the behavior of the chemical products of water radiolysis can be visualized, enabling an intuitive understanding of the water radiolysis and its chemical reaction with DNA (see Fig. 1).

The developed code is expected to be applied to dramatic advances in medical research, such as the optimization of "FLASH radiotherapy" and the sophistication of other radiation therapy plans. Furthermore, it can be applied not only to elucidating the DNA damage induction mechanisms in the field of life sciences but also to analyzing the amount of hydrogen generated in nuclear reactors in the field of nuclear engineering.

The developed PHITS-Chem code was included in the PHITS package and distributed to more than 10,000 users. These outcomes were published in the British scientific journal "Physical Chemistry Chemical Physics" on March 21, 2025. At the same time, an illustration created using the developed code was featured on the back cover of the journal (see Fig. 2).

[Acknowledgements] Fig. 2 was reproduced with permission from "Physical Chemistry Chemical Physics."
Article information: https://pubs.rsc.org/en/content/articlelanding/2025/cp/d4cp04216f

JAEA HP Press release (Japanese only)

The “starting point” of radiation-induced cancer risk!  – The breakdown of water around DNA disturbs the genetic information of life – 

2025.03.31

Nuclear Science and Engineering Center (NSEC) in collaboration with Ibaraki University, Hokkaido University, and Kyoto University, has demonstrated that radiolytic products of water around DNA can derange the genetic information of life. This result provides a new basic concept for the starting point of carcinogenesis caused by radiation exposure.

Radiation-induced cancer risk is estimated based on models because epidemiological data are scarce in the low-dose range. Some models employ “no threshold” models, which assume that a cancer risk exists even at low doses, and others employ “threshold” models, which do the opposite (Fig.1 (a)). Currently, the “no threshold model” is adopted and radiation control is conducted with a margin of safety. Although the accumulation of scientific knowledge on various processes is necessary to understand and evaluate the risk of carcinogenesis due to radiation because experimental detection of DNA damage which is starting point of carcinogenesis is still very difficult.

Our study aimed to elucidate the formation mechanism of complex DNA damage using computer simulations. Here, we focused on the formation of DNA damage induced by the radiolytic products of water around DNA. The OH radicals and hydrated electrons generated by the water radiolysis react with DNA cause DNA strand breaks and base damage. Therefore, we simulated the random motions of the products and calculated the probability of DNA damage occurring through reactions with DNA.

Our result elucidated that when water in the vicinity of DNA is degraded, complex DNA damage, in which strand breaks and base lesions are densely generated, is formed at a probability of about 1/50 of that of repairable isolated damage (Fig.1(b)). When such complex damage is formed, the damage strongly inhibits DNA repair enzymes, which induces mutation in cells and may eventually lead to carcinogenesis. Our results support the “no threshold” model of carcinogenesis risk. This finding is expected to become a new basic concept for radiation protection in the future. This study also provides deeper understanding of low-dose exposure from the viewpoint of DNA damage. We will plan to expand our research to the evaluation of DNA damage yield in high-dose radiation fields, which is important in radiotherapy.

The results have been published online journal “Communications Chemistry” in Nature Portfolio (https://www.nature.com/articles/s42004-025-01453-x) on March 6, 2025 (10:00 London time).

JAEA HP Press release (Japanese only)

Breakup of Molten Fuel into a Large Number of Small Droplets in a Nuclear Reactor and Visualization of the Phenomenon in Three Dimensions – Towards an understanding debris formation process – 

2025.03.25

Fig. 1 Overview of the developed visualization method

The Nuclear Science and Engineering Center (NSEC) has developed a method to visualize the phenomenon of liquid breaking up into a large number of small droplets in three dimensions (3D) and has deepened the understanding of the debris formation process.

In a severe accident at a nuclear reactor, the fuel in the reactor melts and falls into a lower coolant pool, where it breaks up into a large number of small droplets and spreads out. When the molten fuel and broken-up droplets cool and harden, they form fuel debris. Especially in the case of a shallow pool, the molten fuel impinging on the floor breaks up into droplets, so the fuel debris is formed in such a very complex situation. If we can clarify the fuel debris formation process, we will be able to contribute to the decommissioning of the Tokyo Electric Power Company Holdings, Inc, Fukushima Daiichi Nuclear Power Station (1F) by interpreting the actual debris formation process. In addition, we will be able to further improve the safety of nuclear reactors by managing severe accidents in advance. However, because it is extremely difficult to experimentally visualize and measure the phenomenon of liquid breaking up into a large of small droplets, we have not been able to obtain a detailed understanding of the debris formation process.

In this study, we have developed a method to visualize the phenomenon of liquid breaking up into droplets in 3D. In addition, by processing 3D visualization data with a computer, it became possible to measure the size and velocity of each droplet with high precision (see Fig. 1). Using these methods, we conducted experiments simulating the situation where a molten fuel falls into a shallow pool in a severe accident. As a result, it was found that droplets form with the “surfing pattern” caused by the velocity difference between the two simulated liquids and a centrifugal force, or the “liquid film rupture pattern” caused by gravity. Thus, for the first time in the world, we achieved to observe in detail the phenomenon of liquid breaking up into a large number of small droplets. In addition, through more detailed observation and high-precision measurement, we have deepened the understanding of the debris formation process. This achievement will contribute to the decommissioning of 1F and to the improvement of reactor safety.

This achievement was published in the professional journal, Physics of Fluids, on March 10, 2025.

【Paper information】
Journal: Physics of Fluids
Title: Atomization Mechanisms in the Vortex-like Flow of a Wall-impinging Jet in a Shallow Pool
Authors: Naoki Horiguchi¹, Hiroyuki Yoshida¹, Akiko Kaneko², Yutaka Abe³
Affiliation: ¹Nuclear Science and Engineering Center, Japan Atomic Energy Agency, ²Institute of System and Information Engineering, University of Tsukuba, ³Professor Emeritus, University of Tsukuba
DOI：10.1063/5.0253743

JAEA HP Press release (Japanese only)