2020 Volume 69 Issue 2 Pages 165-176
Objectives: In case that an accident occurs at a nuclear power plant etc., radioactive iodine may be released into the environment. When it is taken into the human body through breathing or food and drink, it accumulates in the thyroid gland and may cause thyroid cancer after several years to several decades due to radiation exposure. However, taking stable iodine can reduce internal thyroid exposure. In this study, it is discussed the establishment of people-centred stable iodine prophylaxis from the view point of risk-benefit analysis and interventional simulation in local areas, based on gender and age-specific thyroid cancer risk.
Methods: The number of excess thyroid cancer incidence from acute thyroid exposure to low LET ionizing radiation and the lifetime thyroid cancer risk per equivalent dose for gender and age at the time of exposure were estimated. The predicted equivalent dose of thyroid, providing at all times the net benefit of taking stable iodine, as an interventional level was calculated from a risk-benefit analysis. Furthermore, the number of thyroid cancer occurrences and the incidence of adverse events related to taking stable iodine were predicted from the interventional simulation of stable iodine prophylaxis in two virtual areas.
Results: The lifetime thyroid cancer risk per thyroid equivalent dose unit（1 Sv）was highest at 10.5 and 3.3, respectively, per 1,000 people, in female children and male children under 5 years of age at the time of exposure. The predicted equivalent dose of thyroid as an intervention level decreased with increasing severity of adverse events, and increased with decreasing the effect of risk reduction. The interventional simulations showed that the predicted number of adverse events could be higher in elderly groups albeit the low lifetime risk.
Conclusions: The stable iodine prophylaxis may be applied for the groups with a greater lifetime risk among the residents, based on the gender and age-factors , but not for all of the residents. However, there are circumstances that must be taken into consideration in local areas, such as available emergency medical system at nuclear accidents and the expectable interventional effects, and it is necessary to address them cooperatively through risk communications between local government agencies and residents. A stable iodine prophylaxis system that matches the characteristics of local areas and may be understood by the residents, namely a people-centred stable iodine prophylaxis system should be established.
