This review paper introduces the concepts and backgrounds of several outstanding activities and researches, selected by us, on radon/thoron and naturally occurring radioactive materials (NORM) for the past 30 years in Japan. The content covers regulations on safety management of radioactive residues based on the graded approach; the development of a radon/thoron measurement tool and its worldwide use; experiences on large-scale inter-comparison calibration tests for radon/thoron laboratories, and on editing review books for experts and beginners; and improvement of public literacy on radiation. We believe Japan has been one of the leading countries in radon/thoron and NORM researches and related activities. We hope the experiences and knowledge of Japan will continue to support and help the next generationʼs development of researches and activities in fields relating to radon/thoron and NORM around the world.

The absorbed dose rate in air was measured all over Phu Quoc Island, Vietnam after infrastructure projects were undertaken, and changes on dose rates related with these projects were evaluated. The median (range) absorbed dose rate in air for the whole island was 48 nGy/h (19 – 110 nGy/h); as a consequence, dose rate was increased 1.3 times compared to that before infrastructure projects. In the dose rate distribution map, the impacts on dose rate related with constructions of hotels, resorts and roads were clearly displayed. Phu Quoc Island was a sensitive area to changes of absorbed dose rates in air because the original radiation level was low.

The coastal belt of Karunagappally, Kerala, India is known for high natural background radiation (HNBR) from thorium-containing monazite sand. A cohort of all residents in Karunagappally was established in the 1990s to evaluate the health effects of HNBR. Following the cohort of 149,585 residents aged 30-84 for 19.1 years on average, approximately 2,851,688 person-years of observation were accumulated. The cumulative radiation dose for each individual was estimated based on outdoor and indoor dosimetry of each household, taking into account sex- and age-specific house occupancy factors. Using Karunagapally cancer registry, 6,804 cancer cases excluding leukemia were identified by the end of 2017. Poisson regression analysis of cohort data stratified by sex, attained age, follow-up periods and the original/additional subcohorts estimated an excess relative risk of cancer excluding leukemia as -0.05 Gy^-1 (95% CI: -0.33, 0.29) when adjusted for education, bidi smoking, tobacco chewing, and alcohol drinking in a statistical model. In site-specific analyses, no cancer site was significantly related to cumulative radiation dose. Leukemia was not significantly related to HNBR, either.

Dual energy-computed tomography (DE-CT) can discriminate between materials using the material density obtained by two types of X-ray energies. This study investigated the characteristics of the water density value (WDV) used as a prognostic indicator. WDV with any contrast medium concentration was measured using a bottled diluted contrast medium. In addition, we studied retrospective reviews of 117 patients who underwent DE-CT between 2013 and 2018 and compared them with WDVs before and after contrast enhancement (CE). The WDVs were obtained from the abdominal aorta and superior vena cava. In the ex-vivo study, the WDV decreased slightly by of 0-10% contrast medium concentration, however, it increased gradually above 10%. The number of patients whose WDV of the CT image increased after CE-CT were 28 in the arteries and 50 in the veins. The results suggested that the concentration of the contrast medium was over 10% in arteries and veins. The differences between WDVs in arteries and veins obtained from CT images were very small, with or without CE. Therefore, it was revealed that WDV was less affected by the difference in arteries and veins, or by using contrast medium.

This study aimed to report a simple approach dosimetric tool for ambient risk organs/tissues (targets) to thyroid uptake (source) for ¹³¹I radiopharmaceutical of Gravesʼ disease. The dosimetric tool introduced in this study is based on the mean absorbed dose estimates and calculations by the Monte-Carlo code in radiation transport of particle heavy ion transport code system (PHITS), which is incorporated with Marinelli-Quimbyʼs formula in clinical use on therapeutic nuclear medicine using the International Com-mission on Radiological Protection (ICRP) reference adult male computational voxel phantom. More-over this feature can perform those dose estimates without fully calculating specific absorbed fractions (SAFs) or S-values relative to the radiation transport and energy deposition from source within targets, in-stead using the main absorbed dose (334.5500 Gy) of thyroid uptake determined by Marinelli-Quimbyʼs formula and precomputed dose ratio tables derived from PHITS between the thyroid uptake and ambient risk targeted organs/tissues (spleen, liver, pancreas, and thymus) and also easily working on 2D and 3D display procedure for radiation transport and energy deposition distribution mappings on ParaView and ANGEL (the latter is installed in PHITS) applications. To investigate the validation of our proposed simple approach dosimetric tool, we have compared it with different methods (PHITS direct method, ICRP Pub.53, IDACDose2.1, and OpenDose) to the mean absorbed dose estimates in the thyroid gland and those ambient risk targeted organs/tissues. We have found that it is in generally good agreement with those dose estimate results obtained in our proposed simple approach and others, and also represents that the PHITS calculation coupled with the Marinelli-Quimbyʼs formula is quite reliable enough to with-stand an absorbed dose estimate tool for other uptake organs/tissues working on sources themselves. It would seem that the proposed dosimetric tool has allowed any attending physician and medical physicist to provide easy and simply absorbed dose estimates for every normal and risk ambient organs/tissues to thyroid uptake in the administrated ¹³¹I radiopharmaceutical in therapeutic nuclear medicine on Gravesʼ disease.

A car-borne survey of absorbed dose rate in air (referred to as “dose rate”) was conducted on Oshika Peninsula, Miyagi Prefecture located in the northeastern part of Japan in the early spring; measurements were made using a 2-in.×2-in. NaI(Tl) scintillation counter. The influence of snowfall on the dose rate was evaluated, and the relationship between the distribution of the dose rate and surface geology was also discussed. The dose rates were seen to increase due to snowfall, although the radon concentration which would be related to its progeny concentration was reported to be relatively low in winter to spring. This might be because of the continental air masses containing high concentrations of radon and its progeny which come from the Asian continent to Japan in winter. The dose rates were found to be high in the middle and eastern parts of the peninsula and low in the southern and northwestern parts. The results indicate the correspondence between the distributions of dose rates and surface geology at the high dose rate areas.

Hirosaki University has been designated by the Nuclear Regulation Authority as an Advanced Radiation Emergency Medical Support Center (AREMSC) and as a hospital which accepts radiation emergency medical patients in Japan. In radiation emergency medicine, blood analysis is required to check the patientʼs health and estimate radiation dose. As the medical staff in Nuclear Emergency Core Hospitals and Nuclear Emergency Medical Cooperative Institutions do not have much experience in requesting biodosimetry laboratories for chromosome analysis, they are often unsure about which blood collection tubes to use and how blood should be stored after collection. Thus, AREMSC in Hirosaki University has prepared and provided guidelines for blood collection, management and shipping. Furthermore, AREMSC in Hirosaki University has also been developing young human resources as one of AREMSCs in Japan. AREMSC in Hirosaki University has provided training materials for developing human resources in biological dose evaluation, which is one of the main missions in AREMSC. This article introduces an overview of the guidelines for blood collection, management and shipping, and an excerpt of training materials in cytogenetic biodosimetry at AREMSC in Hirosaki University.

This is a report on the sixth Educational Symposium on Radiation and Health by Young Scientists (ESRAH2019) held at Hirosaki University in Japan on September 14, 2019. Nuclear power plants play a major role in catering to Japanʼs energy demand, and therefore, emergency response and coordination in case of radiation-related accidents are essential for nuclear facilities. In the wake of the accident at the Fukushima Daiichi Nuclear Power Plant followed by the Great East Japan Earthquake in 2011, the establishment of a radiation emergency response system is currently underway, and it also takes into consideration the research on the effects of radiation on human tissues. Further to this, human resources with knowledge about radiation who can respond to radiation accidents in an emergency should be trained further. The ESRAH has been held jointly by Hirosaki University and Hokkaido University since 2014. This symposium aims to provide young researchers the latest developments and knowledge on radiation by inviting eminent researchers from across the globe and promoting the exchange of ideas among young researchers from various radiation fields. At ESRAH2019, four educational lectures by eminent researchers from Ireland, Indonesia, Hungary, and Italy and 30 poster discussions by young researchers were held. The young researchers were provided a meaningful opportunity to build an international research network.

The virtual meeting of the 3rd workshop on Radiation Research and Its Related Issues and the 7th Educational Symposium on Radiation and Health by Young Scientists (ESRAH2020) Joint Symposium was held online during November 21–23, 2020. This symposium brought together diverse researchers and graduate students (3 lecturers, 13 oral presenters, and 52 attendees), who had lively exchanges of opinions on various issues related to radiation. In addition to the lectures on radiological research under the pandemic of coronavirus disease 2019 (COVID-19), radionuclides in food, and radiological emergency response, there were poster presentations by graduate students and young researchers. In this report, we summarize the lectures and oral sessions, and describe our experience of holding a virtual symposium, which was our first such attempt, necessitated owing to the COVID-19 restrictions.