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Thyroid Monitoring for Residents of Disaster-affected and Neighboring Areas

The devastating environmental contamination caused by the nuclear disaster at the Fukushima Daiichi Nuclear Power Station of The Tokyo Electric Power Company is exposing the residents of the disaster-affected areas to health risks attributable to radiation exposure, and fear of the development of I-induced thyroid cancer, which is a stochastic effect of radiation and is particularly high. As part of the response to nuclear disasters by the government of the municipality where the nuclear power station is located and in operation and by the governments of neighboring municipalities, it is necessary to conduct thyroid monitoring for the purpose of alleviating the fears of residents of the disaster-affected areas as well as those living in the contaminated, even if only slightly, neighboring areas (local residents). This health monitoring needs to be implemented without delay in the case of a disaster along with dissemination of a portable type thyroid monitoring system available at evacuation centers, etc. for assessing thyroid exposure doses. The establishment of a system for developing personnel ready to perform monitoring is also essential. Assessing thyroid exposure doses is indispensable as a means of assuring local residents not only of safety but also of security from the risks of radiation. To date, contamination has not been detected in people, except for residents contaminated by a large amount of iodine, by employing the mobile type of thyroid monitoring system. However, when local residents seeking security desire thyroid monitoring, it is preferable that a portable type simplified thyroid monitoring system be used as a means of ensuring security against radiation.


Introduction
The catastrophic environmental contamination caused by the radioactive materials released at the time of the nuclear dis- While screening, though imperfect, was conducted, no public institutions planned organized exposure assessments, assessments and control of internal exposure above all other issues, for all victims until mid-June. Behind this issue is a discrepancy between safety and security against exposure. Besides, there is the fact that both special thyroid monitoring systems necessary for assessing thyroid internal exposure and personnel capable of performing it are scarce from a technical standpoint. Thus, it is presently impossible to perform thyroid monitoring on many local residents in a short period of time.
As of July 2011, 131 I with a short half-life has already decreased, and there is little likelihood that another internal exposure will occur unless further 131 I is released. In addition, iodine cannot be detected in people at present, except for those exposed to several Sv of iodine, even if high-sensitivity measuring instruments (whole body counter, etc.) are used. According to an announcement from the government, medical treatment must have been provided for residents who might have received large doses of 131 I. Thus, at this point in time, thyroid monitoring using high-sensitivity measuring instruments, from the aspect of exposure control, is entirely meaningless scientifically.
Thyroid monitoring of local residents is important at present in that it is performed on those who desire thyroid monitoring for security. Probably, many residents will want to receive monitoring for their own sense of security. This means that it is necessary to perform thyroid monitoring on a large number of local residents in a short period of time. It should be noted, however, that the personnel responsible for monitoring need to explain to those who will undergo monitoring prior to the actual monitoring that it will only show that the exposure dose is below several Sv. In addition, the government of the municipality where the nuclear power station is located and in operation, and the governments of the neighboring municipalities should review their thyroid exposure control actions for local residents in anticipation of future nuclear disasters with the current state of thyroid monitoring taken into account.
These situations signify the necessity of making efforts to establish a system capable of conducting thyroid monitoring on a large number of local residents in a short period of time.
The purpose of this report is to propose a method for assessing thyroid exposure doses based on measured values and a feasible approach to developing a versatile thyroid monitoring system and personnel ready for thyroid monitoring in order to assess and control the internal exposure of local residents by radioactive iodine and thereby resolve the aforementioned issues.
2. Importance of thyroid exposure dose assessment of local residents The timetable for calming this situation and resolving the nuclear disaster was announced, but there is apprehension that the disaster will take a longer time to reach a resolution. Under these circumstances, establishing a medical care system, an exposure control system in particular, for nuclear power station operators and local residents is an urgent necessity. The contamination caused by the disaster spread widely from Fukushima Prefecture, which was directly damaged, to neighboring municipalities. All prefectures in which a nuclear power station is located and in operation, as well as neighboring municipalities, should, therefore, establish and maintain an exposure control system in preparation for future nuclear disasters.

Screening and triage
At the disaster site, triage is conducted to determine treatment priority for the injured. It is also necessary to perform screening intended to determine whether radiation medicine should be provided to the injured. According to a report, the following were performed in the screening inspection in the Fukushima nuclear disaster: (1) survey meters were used to measure surface contamination to determine whether decontamination was required with the counting rate or dose rate used as an index; and (2) thyroid contamination monitoring was conducted, and stable iodine was distributed as a measure against internal exposure if higher contamination than the standard level was detected.
Information conveyed from the site, however, indicates that thyroid monitoring was not always performed in actual screening. This implies that even higher exposure than the specified thyroid screening level is occasionally overlooked. On the other hand, lower exposure than the thyroid screening level is considered to represent an uncontaminated state, but this is not actually correct. Since the screening level is set for triage, lower contam-ination than the screening level must not be neglected. The exposure doses of all residents should be assessed even if contamination is lower than the screening level.

Fear about radiation and radiation PTSD
It is widely known that victims of earthquakes or other disasters suffer Post Traumatic Stress Disorder (PTSD), and news that many experts visited the areas damaged by the Great East Japan Earthquake to deal with personnel suffering from PTSD were broadcast. In addition, organizations involved in PTSD deliver information about psychological care through their websites, etc.
The residents of the areas contaminated by the Fukushima nuclear disaster were exposed to variable amounts of radiation.
Medical treatment is given to the residents with higher contamination than the screening level, but their fears about the development of cancer in the future persist. On the other hand, those who are below the screening level and are not considered contaminated also express fears. For these residents, there is an underlying fear about cancer, which is a stochastic effect.
Mothers with infants, as well as children who already understand the meaning of exposure to radiation, in particular, must live with this fear for many years to come. The possibility that they will become unstable mentally and develop PTSD (radiation PTSD) under these circumstances cannot be denied.
In assessments of radiation exposure and contamination, comparisons between the measured values of exposure doses, dose rates, contamination concentration, etc. and legal regulation values are indispensable. Objective numerical data will become necessary for dealing with fears about radiation.
Obtaining objective information, or exposure doses, is expected to dispel the fears of many residents. Those in a position to use such numerical data, however, must not say that victims are safe even if their contamination is below the legal regulation levels because safety and security are not realities for these individuals due to past dubious disclosures of information about radiation contamination and radiation exposure.
There may be also residents who will not be able to eliminate their fears and will become unstable mentally, even if they have access to objective data on exposure doses. In this case, there will be no choice but to determine that they have sustained radiation PTSD. Nonetheless, assessing the exposure dose of each individual is still indispensable for mental care.
At present, there are no experts on radiation PTSD. Thus, PTSD experts and radiation experts must collaborate with one another to establish specific care approaches for those suffering from radiation PTSD in the future.

Importance of thyroid equivalent dose assessment
The most important aspect of the internal exposure caused by a nuclear disaster is thyroid exposure by radioactive iodine. Since

Necessity of portable type monitoring system
Thyroid monitoring, which aims to estimate the internal exposure doses of the thyroid glands caused by radioactive iodine, is generally conducted using a special, high-sensitivity instrument, such as a whole body counter (WBC) or thyroid monitor. The purpose of using these instruments is different from that of survey monitors with low measurement accuracy employed for screening. If wide areas are affected by a disaster, like the Fukushima nuclear disaster, it is impossible to monitor local residents with these instruments in a short period of time, taking into account the number of residents to undergo measurement and the number of instruments available.
To perform thyroid monitoring on a large number of local residents in a short period of time, many of the portable type simplified monitoring systems and many measurement technologists familiarized with monitoring skills are needed. It is easy to establish a scheme for making these systems available and training technologists.

Portable type simplified thyroid monitoring system
A portable type simplified thyroid monitoring system consists of the same units as those making up a thyroid uptake measuring instrument for nuclear medicine. As a collimator for a detector and a support, those of the uptake measuring instrument can be used (Fig. 1a). This monitoring system can be clamped using a supporting pole for intravenous drips if it is not equipped with a support or another suitable component (Fig. 1b). In this case, no cylindrical tube made of lead for the detector is provided, but it is necessary to set a cylindrical tube made of lead only on the NaI (Tl) detector. Connect the NaI (Tl) detector to a high-voltage power supply unit (HV), a multi-channel pulse height analyzer (MCA), and a PC (Fig. 1c). Although these units are independent (Fig. 1c), their performance is equal to that of the components of the thyroid uptake measuring instrument for nuclear medicine. In this configuration, the thyroid monitoring system is capable of measuring thyroid exposure with an error level equivalent to that of the uptake measuring instrument.
Another type is also available, which can be directly connected to a detector with HV and a PC containing MCA and other components (Fig. 1d).
The lower detection limit of the simplified thyroid monitoring system is 600 Bq for 10-minute measurement, and the thyroid equivalent dose in this measurement is 0.17 mSv in the case of an adult or 1.45 mSv in the case of a 1-year-old child.
Although the thyroid monitoring system can ensure a satisfactory level of accuracy for adults in 10-minute measurement, it may not be sufficiently capable of providing a high level of accuracy in measurement of 1-year-old children (Fig. 2

Progress toward implementation of thyroid monitoring
This monitoring system is easy to carry, install, and operate, and it is probably possible to prepare a sufficient number of systems at relatively low cost.
In addition, the accuracy of these monitoring systems can be