Exposure of cells to ionizing radiation (IR) results in DNA damage, among which DNA double strand breaks (DSBs) are the most deleterious to human health. Although DSBs are efficiently mended by DSB repair systems, intolerant radiation doses cause unreparable DSBs, which persistently activate DNA damage signaling pathway. As a result, cell death is executed. A number of cell death modes have been described, including apoptosis, premature senescence, necrosis, and autophagy. While the mode of cell death is dependent on the stimuli given to cells, apoptosis and premature senescence have been documented in several studies as the two representative modes of cell death in response to radiation exposure. Particularly, it is becoming more aware that premature senescence is the common cause of cell death in various nonhematopoietic tissues, including epithelial tissues, mesenchymal tissues, and endothelial and lymphatic cells. Further studies have demonstrated that secretory phenotype is common to senescent cells, and soluble factors secreted from senescent cells, such as cytokines, chemokines, growth factors, and matrix remodeling factors, are those deeply involved in the execution of both acute and late radiation health effects. Moreover, recent evidences have demonstrated a close connection between radiotherapy-induced senescence and the development of adverse effects. Current review overviews the modes of cell death caused by radiation exposure, and discusses the physiology of cellular senescence, molecular mechanisms of radiation-induced premature senescence, significance of premature senescence in tissue reaction and late effect. Moreover, recent approaches towards the amelioration of health effects by senolytic chemicals that enable elimination of senescent cells from tissues will be presented.

There are many calibration facilities of radon gas in the world, which are used to keep a measurement quality of radon mainly for purpose of radiation protection. Although there is only a limited number of techniques of a primary standard, each calibration facility employs several different techniques to establish a secondary calibration. The article summarized a status of radon traceability and the techniques used in the radon calibration facilities as well as the characteristics of each technique. In terms of geographical characteristics of calibration facilities, there was a biased distribution of a primary standard; only the US and Korea have a primary standard except in Europe. For differences in the technique used, it was found that operation modes may have an influence on the maximum radon concentration in the chamber and the time to reach a stable concentration. Types of radon sources may also affect the radon concentration in the chamber due to the difference in the emanation power of radon gas. The findings are expected to be utilized for the design and development of new radon calibration chambers in the future.

The development of high-precision dose calculation techniques for the radiotherapy of tumors has enabled treatment with fewer side effects in normal tissues. However, a crucial problem remains wherein some cancer cells may acquire radioresistance or cancer stem cell (CSC) characteristics and cause recurrence and metastasis. The acquisition of these phenotypes is associated with complex molecular signaling and biological processes that remain unclear. In addition, these phenotypes are originally inherent within the tumor and are induced by external factors such as radiation. Therefore, a better understanding of the mechanisms underlying radiosensitization and how these phenotypes are acquired is essential for improving radiotherapy outcomes. This review outlines the current findings on the association of radiotherapy with CSC induction, signaling pathways and radioresistance processes, as well as therapeutic strategies aimed at the radiosensitization of these phenotypes.

Nagasaki University established four satellite offices within a 30-km radius of the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japanʼs Fukushima Prefecture: in Kawauchi Village, Tomioka Town, Okuma Town, and Futaba Town. To evaluate the external and internal exposures attributable to the FDNPP accident, environmental radioactivity levels continue to be investigated at these sites. Our previous studies examined specific and regional case studies based on in-situ environmental radioactivity monitoring activities. Their findings suggested that current external and internal exposure doses of radiocesium have been controlled at the lower limit of the current “exposure situation” (1–20 mSv/y, International Commission on Radiological Protection) in the evacuation order-lifted areas of Kawauchi Village and Tomioka Town. However, conducting long-term follow-up studies, such as environmental radioactivity monitoring, developing countermeasures for further decontamination in the difficult-to-return zone, and implementing restrictions on the consumption of local foods, are all needed to reduce unnecessary radiation exposure to residents and workers, particularly since radiocesium derived from the FDNPP accident remains in some areas around the site. These case studies have clarified scientifically the temporal dose levels and aided in the development of environmental remediation measures that consider radiation exposure in the recovery and reconstruction process following the accident.

We validated the calculation accuracies and times between the pencil beam algorithm (PBA) and the Monte Carlo (MC) algorithm in the new proton pencil beam scanning system. Thirty-three (homogeneous phantom) and three (heterogeneous phantom) uniform-dose plans were verified for cubic targets. These plans were calculated using the PBA and five MC statistical uncertainties of 0.3%, 0.5%, 1.0%, 1.5%, and 2.0%. We also evaluated the required dose calculation times per beam with the statistical analysis. Then, eight clinically realistic beams were validated as the end-toend test. The dose differences of 0.3% and 0.5% uncertainty MC plans were satisfied our tolerance (< ±3.0%). All five uncertainty MC plans improved at least the average/minimum gamma score from 93.8%/33.5% to 98.5%/88.9% for homogeneous (2%/2 mm) and 96.7%/83.9% to 98.8%/94.1% for heterogeneous (3%/3 mm) than PBA plans. However, the average calculation times of 0.3% and 0.5% uncertainties in MC plans were 15.5 and 5.8 times longer than in PBA plans (p < 0.001). The endto-end tests satisfied the acceptable with a statistical uncertainty of MC below 0.5%. Although the dose calculation times would be significantly increased, we suggest that the statistical uncertainty of MC below 0.5% is appropriate for clinical use with PBS plans.

Depending on brain tumor type, radiotherapy with various irradiation methods may be an effective treatment even for lesions for which surgical treatment is difficult; however, neurocognitive dysfunction may occur as an adverse effect. Neurons divide infrequently and are recognized as radiation resistant; however, few reports have investigated the effects of radiation on the intercellular network. We analyzed the impact of radiation exposure on the repair kinetics of DNA damage and the electrophysiological changes of synaptic currents in cerebral cortical neurons, employing primary culture technique. Cortical neurons (14 days in vitro) were subjected to varying X-irradiation doses. DNA double-strand breaks were induced in cultured cortical neurons by high-dose X-irradiation; however, these cells have the ability to repair severe DNA damage and are resistant to radiation. An electrophysiological investigation revealed that the inter-event intervals of miniature excitatory postsynaptic current (mEPSC) in X-irradiated cortical neurons were significantly longer, while the amplitude showed no change in comparison to 0 Gy-irradiated cells. These results suggested that the exposure of neurons to radiation led to a decrease in the frequency of the mEPSC, which affected the synaptic network, which supports the neurocognitive function despite being less likely to cause cell death or severe DNA damage.

Naturally radioactive sources were developed using three easily available and familiar substances: potassium chloride, instant coffee, and kelp. The radiation fields that they generated were actual measurements using various instruments to adapt the sources to school radiation education. It was quantitatively found that the potassium chloride source can be used for qualitative experiments on β-rays. The latest national Courses of Study published by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) have been applied since 2020. By the results of our measurements with the Courses of Study, an example of experimental training using naturally radioactive sources: “Absorption training Experiment of β-rays Using Shielding Materials” was developed. We believe that the widespread application of naturally radioactive sources made of familiar materials will make it easier for schoolteachers to carry out radiation experiments in their classes and contribute to establishing the publicʼs literacy on radiation.