According to the principle of optimization, known as "As Low As Reasonably Achievable (ALARA), that efforts should be made to reduce the exposure dose of the public and professionals as much as possible.21–23 This ALARA principle also applies in radiation emergencies. However, in the event of a radiation emergency, when an EMR responds to an exposed and/or contaminated patient, saving the life of the patient being the priority and the determination of the treatment strategy, including an exposure dose evaluation, is important.24,25 The management of the exposure dose of professionals, such as EMRs, makes it difficult to achieve the ALARA principle because of the priority placed on saving patients' lives. It is conceivable that an emergency medical doctor, nurse, and health physicist will encounter situations where they will deal directly with contaminated victims and evacuees. In those situations, it would be difficult to secure sufficient distance and time for unknown contamination. EMRs wear a personal dosimeter to measure the exposure dose and wear protective clothing to prevent contamination. However, these measures cannot predict the exposure dose in an emergency. To provide emergency radiation medicine, it is very important to predict and manage the exposure dose of EMRs. Protocol and planning need this information for strategy planning, which would include replacement personnel requirements and permitted activity time.26
The results of this simulation study were obtained using the PHITS code for which benchmarks have already been established. When compared with the actual measurement experiments, the simulation values were comparable and did not underestimate actual values. The relative error rate was within 14% overall, a sufficiently reliable value (Fig. 2). Based on the simulation results of this study, when EMRs respond to victims with contamination exceeding OIL4, it was found that the exposure dose of an EMR did not approach the dose limit when considering the actual activity time (Fig. 3, Table 2). In the case of contaminated injuries caused by theft of or accidents involving radiation sources for medical and industrial applications, it was shown that an EMR might suffer exposure ranging from 1 mSv to 100 mSv (Fig. 4, Table 2). The exposure dose of an EMR who provides radiation emergency medicine is the exposure dose when the contaminated area of the victim is not decontaminated at all. It is necessary to keep in mind that the exposure dose of both the patient and EMR can be reduced by performing appropriate decontamination after the patient's lifesaving measures are taken. Accidents in which a high-radioactivity source is attached to a patient are rare. It is unlikely that exposure to EMR by radioactive substances attached to the patient will cause a deterministic effect. Still, it is important to control the exposure dose for radiological protection.
Several studies emphasize the anxiety related to radiation among medical professionals and the importance of radiological protection education. For example, Sato et al. conducted a questionnaire survey of nurses working at core hospitals in Fukushima Prefecture after the FDNPP accident and revealed that many nurses were considering retirement or migration owing to radiation anxiety and radiation-related health effects.27 Akashi et al. advocated the significance of promptly providing radiological protection information to the Disaster Medical Assistance Teams.28 As reported in these previous studies, it is important to provide radiological protection and radiation emergency medical education for EMRs. The guidelines published by the IAEA in 2020 show the importance of obtaining the cooperation of medical physicists with experience in radiation emergencies.29 Research data show that improving the activity capacity of EMRs and reducing their anxiety is critically important in radiological protection.
The results shown in Figs. 4 and 5 can be a quick reference data of EMRs' exposure doses, assuming several scenarios involving medical and industrial radiation sources. Such an event is rare, but they have occurred, as shown by the Brazilian Goiânia accident and the American Indiana accident. There are only two accidents with radiation measured at the highest level 7 in INES: the ChNPP accident and the FDNPP accident. Still, the overall number of radiological accidents is more than 600 in the 30 years. Over 2000 incidents have been reported with exposed/contaminated victims.30, 31 In addition to these, the existence of additional threats, such as nuclear terrorism, further shows the importance of radiological protection for EMRs.
Although rare events, once a radiological accident or nuclear disaster occurs, societal anxiety and impact would be enormous. Radiological protection and education before the occurrence of these emergencies are important for EMRs and institutions that will handle radiation emergencies. The research results in this paper will be useful for the education of EMRs. We try to achieve it in our educational work.