Lifetime Risk Assessment of Lung Cancer Incidence for Nonsmokers in Japan Considering the Joint Effect of Radiation and Smoking Based on the Life Span Study of Atomic Bomb Survivors

Shimada, Kazumasa,Kai, Michiaki The Korean Association for Radiation Protection 2021 방사선방어학회지 Vol.46 No.3

Background: The lifetime risk of lung cancer incidence due to radiation for nonsmokers is overestimated because of the use of the average cancer baseline risk among a mixed population, including smokers. In recent years, the generalized multiplicative (GM)-excess relative risk (ERR) model has been developed in the life span study of atomic bomb survivors to consider the joint effect of radiation and smoking. Based on this background, this paper discusses the issues of radiation risk assessment considering smoking in two parts. Materials and Methods: In Part 1, we proposed a simple method of estimating the baseline risk for nonsmokers using current smoking data. We performed sensitivity analysis on baseline risk estimation to discuss the birth cohort effects. In Part 2, we applied the GM-ERR model for Japanese smokers to calculate lifetime attributable risk (LAR). We also performed a sensitivity analysis using other ERR models (e.g., simple additive (SA)-ERR model). Results and Discussion: In Part 1, the lifetime baseline risk from mixed population including smokers to nonsmokers decreased by 54% (44%-60%) for males and 24% (18%-29%) for females. In Part 2, comparison of LAR between SA- and GM-ERR models showed that if the radiation dose was ≤200 mGy or less, the difference between these ERR models was within the standard deviation of LAR due to the uncertainty of smoking information. Conclusion: The use of mixed population for baseline risk assessment overestimates the risk for lung cancer due to low-dose radiation exposure in Japanese males.

Detection Limit of a NaI(Tl) Survey Meter to Measure 131I Accumulation in Thyroid Glands of Children after a Nuclear Power Plant Accident

Takahiro Kitajima,Michiaki Kai 대한방사선방어학회 2023 방사선방어학회지 Vol.48 No.3

Background: This study examined the detection limit of thyroid screening monitoring conducted at the time of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 using a Monte Carlo simulation. Materials and Methods: We calculated the detection limit of a NaI(Tl) survey meter to measure 131I accumulation in the thyroid gland of children. Mathematical phantoms of 1- and 5-year-old children were developed in the simulation of the Particle and Heavy Ion Transport code System code. Contamination of the body surface with eight radionuclides found after the FDNPP accident was assumed to have been deposited on the neck and shoulder area. Results and Discussion: The detection limit was calculated as a function of ambient dose rate. In the case of 40 Bq/cm2 contamination on the body surface of the neck, the present simulations showed that residual thyroid radioactivity corresponding to thyroid dose of 100 mSv can be detected within 21 days after intake at the ambient dose rate of 0.2 μSv/hr and within 11 days in the case of 2.0 μSv/hr. When a time constant of 10 seconds was used at the dose rate of 0.2 μSv/hr, the estimated survey meter output error was 5%. Evaluation of the effect of individual differences in the location of the thyroid gland confirmed that the measured value would decrease by approximately 6% for a height difference of ±1 cm and increase by approximately 65% for a depth of 1 cm. Conclusion: In the event of a nuclear disaster, simple measurements carried out using a NaI(Tl) scintillation survey meter remain effective for assessing 131I intake. However, it should be noted that the presence of short-half-life radioactive materials on the body surface affects the detection limit.

Role and Collaboration of Radiation Protection Experts: Summary of Discussions between the Japan Health Physics Society and the Korean Association of Radiation Protection Related to Tritiated Water

Sasaki Michiya,Yoshida Hiroko,Kai Michiaki,Jeong Yong Hoon,Kim Kyo-Youn,이희석 대한방사선방어학회 2022 방사선방어학회지 Vol.47 No.2

Estimating Organ Doses from Pediatric Cerebral Computed Tomography Using the WAZA-ARI Web-Based Calculator

Etani, Reo,Yoshitake, Takayasu,Kai, Michiaki The Korean Association for Radiation Protection 2021 방사선방어학회지 Vol.46 No.1

Background: The use of computed tomography (CT) device has increased in the past few decades in Japan. Dose optimization is strongly required in pediatric CT examinations, since there is concern that an unreasonably excessive medical radiation exposure might increase the risk of brain cancer and leukemia. To accelerate the process of dose optimization, continual assessment of the dose levels in actual hospitals and medical facilities is necessary. This study presents organ dose estimation using pediatric cerebral CT scans in the Kyushu region, Japan in 2012 and the web-based calculator, WAZA-ARI (https://waza-ari.nirs.qst.go.jp). Materials and Methods: We collected actual patient information and CT scan parameters from hospitals and medical facilities with more than 200 beds that perform pediatric CT in the Kyushu region, Japan through a questionnaire survey. To estimate the actual organ dose (brain dose, bone marrow dose, thyroid dose, lens dose), we divided the pediatric population into five age groups (0, 1, 5, 10, 15) based on body size, and inputted CT scan parameters into WAZA-ARI. Results and Discussion: Organ doses for each age group were obtained using WAZA-ARI. The brain dose, thyroid dose, and lens dose were the highest in the Age 0 group among the age groups, and the bone marrow and thyroid doses tended to decrease with increasing age groups. All organ doses showed differences among facilities, and this tendency was remarkable in the young group, especially in the Age 0 group. This study confirmed a difference of more than 10-fold in organ doses depending on the facility and CT scan parameters, even when the same CT device was used in the same age group. Conclusion: This study indicated that organ doses varied widely by age group, and also suggested that CT scan parameters are not optimized for children in some hospitals and medical facilities.

The Identification, Diagnosis, Prospective, and Action (IDPA) Method for Facilitating Dialogue between Stakeholders: Application to the Radiological Protection Domain

Jacques Lochard,Win Thu Zar,Michiaki Kai,Ryoko Ando 대한방사선방어학회 2023 방사선방어학회지 Vol.48 No.3

This article reviews the experience of applying the Identification, Diagnosis, Prospective, and Action (IDPA) facilitating method as a means of promoting practices of dialogue between stakeholders in the radiological protection field. After presenting the characteristics of the IDPA method and its ability to promote active listening, participation, and dialogue among stakeholders facing complex situations, as well as the procedural aspects associated with its practical implementation, the article describes three examples of the application of the method in the field of radiological protection. The first one presents how the IDPA method supported a debate among decision-makers, authorities, experts, professionals, and representatives of non-governmental organizations about how to engage stakeholders in radiological protection. The second example presents how the IDPA method was used in a series of dialogue meetings to explore the challenges of the post-nuclear accident situation resulting from the Fukushima Daiichi Nuclear Power Plant accident. The third one presents the application of the method in the context of a training course organized by Nagasaki University in the affected area close to the damaged plant. Experience has shown that the IDPA method makes it possible to develop responses to problems posed in very different contexts and, in many cases, to find compromises regarding their solutions. The IDPA method has the merit of allowing each of the participants to better understand the situation they are faced with, even if such a positive result is not always achieved.

SUMRAY: R and Python Codes for Calculating Cancer Risk Due to Radiation Exposure of a Population

Sasaki Michiya,Furukawa Kyoji,Satoh Daiki,Shimada Kazumasa,Kudo Shin’ichi,Takagi Shunji,Takahara Shogo,Kai Michiaki 대한방사선방어학회 2023 방사선방어학회지 Vol.48 No.2

Background : Quantitative risk assessments should be accompanied by uncertainty analyses of the risk models employed in the calculations . In this study, we aim to develop a computational code named SUMRAY for use in cancer risk projections from radiation exposure taking into ac- count uncertainties . We also aim to make SUMRAY publicly available as a resource for further improvement of risk projection . Materials and Methods : SUMRAY has two versions of code written in R and Python . The risk models used in SUMRAY for all-solid-cancer mortality and incidence were those published in the Life Span Study of a cohort of the atomic bomb survivors in Hiroshima and Nagasaki . The confidence intervals associated with the evaluated risks were derived by propagating the statisti- cal uncertainties in the risk model parameter estimates by the Monte Carlo method . JRPR Results and Discussion : SUMRAY was used to calculate the lifetime or time-integrated attrib- utable risks of cancer under an exposure scenario (baseline rates , dose[s] , age[s] at exposure , age at the end of follow-up, sex) specified by the user. The results were compared with those calculated using another well-known web-based tool , Radiation Risk Assessment Tool (Rad- RAT; National Institutes of Health) , and showed a reasonable agreement within the estimated confidential interval . Compared with RadRAT, SUMRAY can be used for a wide range of ap- plications , as it allows the risk projection with arbitrarily specified risk models and/or popula- tion reference data . Conclusion : The reliabilities of SUMRAY with the present risk-model parameters and their variance-covariance matrices were verified by comparing them with those of the other codes . The SUMRAY code is distributed to the public as an open-source code under the Massachusetts Institute of Technology license .