The effect of temperature and shielding on the lower detection limit of a thyroid 131I monitoring system was investigated in an anthropomorphic thyroid-neck phantom fitted with an imaging plate. The phantom was loaded with an 131I aqueous solution and monitored with the imaging plate for 10 min. After exposure, the plates were incubated with or without the shield at 0, 10, 20, 25, 30, or 40°C. The latent image was read out at 0 min to 7 d after exposure. The thyroid equivalent doses corresponding to the detection limit were calculated in six age categories, using the inhalation equivalent dose coefficients recommended by the International Commission on Radiological Protection. The detection limit was distributed between 0.13 and 4.2 kBq, and depended on the age of subjects, elapsed time, temperature, and shielding provision. The maximum detection limit of 4.2 kBq was below the emergency screening level of 30 kBq in Japan. The thyroid equivalent dose corresponding to the detection limit ranged from 0.17 to 46 mSv. From the maximum equivalent dose of 46 mSv, the effective dose was estimated as 1.8 mSv, lower than the annual effective dose limit of 20 mSv for radiation workers. At 2 d after exposure, the measured dose was below the annual effective dose limit of 1 mSv for the public, regardless of age, temperature, and shielding provision. The imaging plate system effectively monitors the 131I thyroid levels in emergency situations.
1Department of Radiological Technology, School of Health Sciences, Gifu University of Medical Science, 795-1 Nagamine, Ichihiraga, Seki, Gifu 501-3892, Japan;
2Tianjin Environmental Protection Bureau, 17 Fukang Road, Tianjin 300191, China;
3Graduate School of Life Sciences, Kumamoto University, 4-24-1, Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan;
4Research Center for Support to Advanced Sciences, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621 Japan;
5Device Engineering and Applied Physics Research Division, National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan;
6Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
The authors declare no conflicts of interest.
For correspondence contact: Shizuhiko Deji, Department of Radiological Technology, School of Health Sciences, Gifu University of Medical Science, 795-1 Nagamine, Ichihiraga, Seki, Gifu 501-3892, Japan, or email at firstname.lastname@example.org.
(Manuscript accepted 21 February 2018)