Tatsuhiko Sato

1. Estimating the shielding effectiveness of facilities and instruments that use radioactive materials and generate radiation is an essential part of the regulatory authorization process. Tradition...

This study presents the application of an analytical model, PARMA, to estimate the population-weighted annual absorbed dose to the lens of the eye due to cosmic rays. Cosmic ray flux data incorporating geographical altitude, together with the global population data from 2020, were used to estimate the global population-weighted annual eye lens dose. The resulting value was 0.267 mGy, ~11% lower than the annual effective dose due to cosmic rays evaluated in the latest UNSCEAR reports. This population-weighted estimate provides a more accurate assessment of background eye lens dose levels and facilitates comparison among the public, aircrew, and astronauts. This estimate also provides a refined baseline for epidemiological studies of lens cataracts.

The American Geophysical Union (AGU) announces the new living collection “Impactful Datasets in Earth, Space, and Environmental Sciences” which recognizes the creation and curation of datasets enabling research, analysis, and decision making beyond what is captured by traditional academic impact metrics. The collection highlights datasets through the dimensions of People, Planet, and Prosperity, and includes a curated set of nominated datasets and accompanying special collection of data papers. Developed with the Earth Science Information Partners (ESIP) community, the nomination and review process initially invites contributors from across research, operations, and public service, to nominate datasets important to their work, and then submit a data paper that expands upon the nomination text for inclusion in the special collection. This commentary highlights the rationale for the living collection, and the process of nomination. The collection serves as a living reference that strengthens data culture, supports reproducible geoscience, and provides enduring access to critical information for science and society.

Objective. Recently, the ICRP developed the pregnant-female mesh-type reference computational phantoms to assess radiation doses to the fetus. To support the generation of reference internal fetal dose coefficients, a fetal specific absorbed fraction (SAF) dataset for photons, electrons, neutrons, and alpha particles will be provided in a forthcoming ICRP publication. Prior to their release, in this study, the computed SAFs were validated and their source- and age-dependent dosimetric trends were systematically analyzed for both maternal and fetal source regions. Approach. Photon and electron SAFs were computed using the Geant4 Monte Carlo code, while neutron SAFs were produced using PHITS, following the methodologies adopted in ICRP Publication 155 for pediatric SAF calculations. Alpha SAFs were defined analytically based on an assumption of complete local energy deposition due to the limited range of alpha particles. Main results. Cross-code validation was performed for photon and neutron SAFs using PHITS and Geant4, demonstrating general agreement across all compared cases. The results demonstrate clear dependencies of SAFs on fetal mass, source–target geometry, and fetal age. For radiations emitted from maternal source regions, SAFs are generally higher for younger fetuses when the source regions are located in close proximity to the fetus, whereas SAFs for older fetuses become larger as the source–target geometry changes with increasing fetal growth. For fetal source regions, SAFs consistently decrease with increasing fetal age due to the increasing mass of fetal target regions with age. Significance. The established dataset provides physically consistent fetal SAFs across multiple radiation types and will be used to support the development of standardized fetal dose coefficients in future ICRP publications.

Objective . Dose-voxel kernel (DVK) convolution provides a physics-based approach for absorbed-dose calculation from nuclear medicine imaging. This study implemented DVK convolution within the particle and heavy ion transport code system (PHITS) and evaluated its performance against Monte Carlo (MC) simulations and clinical dosimetry methods. Approach . Five post-radioembolization ⁹⁰ Y bremsstrahlung single photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/CT (PET/CT) datasets from the University of Michigan Deep Blue Data repository were converted into PHITS-readable formats using the radiotherapy package based on PHITS. Activity distributions were mapped onto CT voxel grids, and DVKs were generated for 24 human tissue materials. A new DVK mode was implemented in PHITS to calculate voxel-wise absorbed-dose rates by convolving tissue-specific DVKs with activity distributions. Performance was evaluated against MC simulations using gamma index analysis, mean absorbed-dose rates within volumes of interests (VOIs), and voxel-wise absorbed-dose differences in liver, lung, and liver–lung interface regions. VOI-based mean absorbed doses were further benchmarked against the local deposition model (LDM) and voxel S -value (VSV) convolution in MIM Software (v7.4.3). Main results . Following one-time DVK generation, DVK mode calculations required ∼40 s compared with >9 h for high-statistics MC simulations. Gamma pass fractions ranged from 92.1%–99.9%, while mean DVK–MC differences in VOI-based dose rates were −1.2 ± 2.9% (SPECT/CT) and −1.0 ± 4.3% (PET/CT). Voxel-wise dose differences showed good agreement between DVK and MC in homogeneous liver tissue, while lung regions exhibited lower absorbed-dose estimates and the liver–lung interface showed increased variability, ( P ₉₅ up to 39%). Compared with MIM, VOI-based dose differences were 9.7 ± 7.2% for SPECT/CT (LDM-based) and −0.1 ± 8.4% for PET/CT (VSV-based). Significance . The PHITS-integrated DVK implementation enables efficient voxel-based dosimetry while maintaining close agreement with high-statistics MC simulations. This framework provides a practical physics-based approach for patient-specific radiopharmaceutical therapy dosimetry.

The International Commission on Radiation Units and Measurements (ICRU) recently published a new report on microdosimetry entitled ‘Stochastic nature of radiation interactions: Microdosimetry’. It provides a comprehensive description of the basic concepts and theories, computational and experimental procedures, and applications of microdosimetry. Evaluation of the relative biological effectiveness (RBE) stands out as one of the most crucial applications of microdosimetry. While such applications have primarily been dedicated to medical physics, the field of radiological protection (RP) also demands the assessment of RBE particularly for tissue reactions due to a recent suggestion made by ICRU and ICRP to change the definition of the operational quantities. This article presents a summary of our recent studies on evaluating RBE for skin reactions and diseases of the circulatory systems based on a microdosimetric kinetic model, together with discussions on the potential role of microdosimetry in the determination of RBE weighting factors used for RP purposes in the future.

WArning System for AVIation Exposure to Solar energetic particles (WASAVIES) is a physics‐based nowcasting system designed to support warning operations for aviation exposure to solar energetic particles (SEPs) by providing near‐real‐time global SEP dose‐rate estimates. On 11 November 2025, ground level enhancement GLE77 occurred and successfully triggered the SEP mode of WASAVIES, demonstrating fully autonomous initiation of global SEP dose‐rate nowcasts during an extreme space‐weather event. The real‐time analysis, however, was partially degraded during parts of the event due to irregular behavior in some neutron monitor (NM) data streams and evolving background conditions. We therefore performed a post‐event reanalysis using a patched version of the operational algorithm to mitigate these issues. Our analysis indicates that GLE77 consisted of multiple peaks and maintained an unusually low rigidity spectral index (as low as 4) for several hours, suggesting that it was the hardest‐spectrum GLE since 2000. The analysis also indicates that the estimated global maximum effective dose rate (including the galactic cosmic‐ray contribution) briefly exceeded the International Civil Aviation Organization Moderate advisory threshold (30 μSv/h) at altitudes of 14 km (∼FL460) and above, but the exceedance was short‐lived (∼10 min) and limited in magnitude and geographic extent. This finding confirms that GLE77 did not warrant major operational responses such as route or altitude changes. Overall, these results validate the operational potential of WASAVIES and identify key upgrades needed to ensure stable, reliable nowcasts for future extreme events.

Microdosimetry does not simply refer to dosimetry with small targets, but rather to dosimetry that accounts for the stochastic nature of energy deposition. The International Commission on Radiation Units and Measurements has proposed using the probability densities of microdosimetric quantities such as lineal energy (y) and specific energy (z) to characterize the radiation fields instead of relying solely on linear energy transfer (LET) and absorbed dose. However, the practical application of microdosimetry remains limited due to significant computational costs associated with evaluating these stochastic quantities in macroscopic contexts such as the human body. To bridge the gap between microdosimetry and macrodosimetry, three approaches have been proposed and implemented: direct integration of track-structure and macroscopic radiation transport codes; integration of a database containing dose-mean values of microdosimetric quantities into macroscopic radiation transport codes; and integration of the analytical microdosimetric function for instantaneously calculating the probability densities of microdosimetric quantities within macroscopic radiation transport codes. This paper comprehensively reviews the conceptual and practical differences between LET and microdosimetric quantities, including their respective computational methodologies. The advantages and limitations of the three approaches are then discussed, followed by a summary of previous research efforts and suggestions for future research directions.