Before the Fukushima Daiichi nuclear power plant accident, radionuclides like ⁹⁰Sr released by atmospheric nuclear detonation tests and the Chernobyl accident have been transported worldwide in the environment and finally taken up by humans through various pathways. In this research, the health risks caused by the prolonged exposure to fallout ⁹⁰Sr through food ingestion pathways were evaluated age-dependently for the reference Japanese since 1945 until 2010, using the mathematical model for evaluating global distribution of ⁹⁰Sr with food ingestion considering the domestic and international food supply in Japan. The model estimates were compared with the monitoring data of ⁹⁰Sr in Japanese total diet and ⁹⁰Sr concentration in food to examine the model validity. The results of this evaluation would be useful for understanding the background situations without the Fukushima accident and give important knowledge for the radiological health risk assessment of this accident.

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We have investigated radiation doses to patients in selected types of examinations in Japan since 1974 and have analyzed the trend of patient radiation doses during a period of 37 years. This study covered regular plain X-ray scanning (including mammography) and computed tomography (CT) scanning. Dose evaluation was performed in terms of entrance skin dose (ESD) for regular plain X-ray scanning, average glandular dose (AGD) for mammography, and volume CT dose index (CTDIvol) for CT scanning. Evaluation was performed in 26 orientations at 21 sites for regular plain X-rays, and for cranial, thoracic, and abdominal scans of children and adults for CT scanning. With the exception of chest X-rays, the dose during regular plain X-ray scanning had decreased by approximately 50% compared with scans performed in 1974, The dose during mammography had decreased to less than 10% of its former level. In scans performed in 2011, doses at all sites were within International Atomic Energy Authority (IAEA) guidance levels. The increasing use of multiple detectors in CT scanning devices was evident in CT scanning. A comparison of doses from cranial non-helical scans performed in 2007 and 2011 found that the latter were higher. An examination of changes in doses between 1997 and 2011 revealed that doses had tended to increase in cranial scans of adults, but had hardly changed at all in abdominal scans. Doses during CT scanning of children were around half those for adults in cranial, thoracic, and abdominal scans. We have ascertained changes in the doses to which patients have been exposed during X-ray scanning in Japan.

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