Effect of 131I biodistribution on measurements using a scanning whole-body counter

Le résumé fourni par la source

To validate the thyroid dose assessment performed at Nagasaki University after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the influence of 131I biodistribution on the direct in-vivo counting measurements by a scanning whole-body counter with two NaI(Tl) detectors was evaluated by a Monte Carlo simulation. The peak efficiency for gamma rays from 131I was calculated for the Bottle-Manikin Absorption (BOMAB) phantom and International Commission on Radiological Protection voxel phantom with a uniform radionuclide distribution in the body and a localized distribution in the thyroid. The ratio of scan peak efficiencies for the BOMAB phantom with the uniform and localized distribution was 1.17 (localized/uniform), while that for the voxel phantom was 1.00. For the voxel phantom, a shielding by the head and tissues covering thyroid reduced the scan peak efficiency for the localized source, resulting in a negligible difference in peak efficiency between the source distributions. The assumption of a completely localized thyroid source is suggested to result in an underestimation within approximately 4% in residual activity assessment, considering 131I biodistribution calculated using ratios of physicochemical forms reported after the FDNPP accident, which represents a scenario with the maximum uncertainty. Consequently, the influence of 131I biodistribution on the scanning whole-body counting was negligibly small under the present conditions, partly due to the detector arrangement with two NaI(Tl) detectors positioned above and below the subject.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.