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Reports in Thyroid Research

ISSN: 2684-4273

Open Access

Five Years of Incorporation Monitoring on an 131I Therapy Ward–Is Incorporation Monitoring Required for Routine?

Abstract

Happel C, Bockisch B, Kratzel U, Grünwald F and Kranert WT

Aim: Aim of this study was to evaluate five years of incorporation monitoring of the nursing staff of an 131I therapy ward. The annual effective dose caused by incorporation of 131I of this profession was compared to the dose limits defined in the German incorporation guideline. Furthermore, the 131I incorporation factor stated in the incorporation guideline was verified using the obtained data.
Methods: The mandatory calculation of the potential possible annual effective dose due to incorporated 131I provides values considerably exceeding the dose limit of 1 mSv/a to the staff of the observed 131I therapy ward. To determine the actual work related incorporation, the 131I activity concentration in 143 urine samples (collection over 24 h) of 14 employees of the nursing staff (subdivided into 1st shift: 07:00–15:00; 2nd shift: 15:00–21:00 and 3rd shift: 21:00–07:00) were examined over a period of five years. The median time of exposure prior to sampling was 5.1 days. 131I was administered to patients mainly as capsules. Preparation was done in a fume hood.
Results: The measured activity concentration in urine samples was related to the individual time of exposure. A constant activity supply for at least three days was assumed. The mean annual effective doses were 0.16 mSv/a for the 1st shift (n=55), 0.12 mSv/a for the 2nd shift (n=48) and 0.02 mSv/a for the 3rd shift (n=40). Therefore all determined annual effective doses were well below the dose limits of the German incorporation guideline. In line with a theoretic “worst case” calculation based on the highest measured individual value of each subgroup a maximum annual effective dose was calculated (1.14 mSv/a for the 1st shift, 1.10 mSv/a for the 2nd shift and 0.23 mSv/a for the 3rd shift). The calculated mean incorporation factors ranged from 1.9 × 10-8 for the 2nd shift to 2.5 × 10-9 for the 3rd shift related to the whole activity administered to the patients during the observation time, and was therefore well below the 131I incorporation factor assumed in the guideline.
Conclusions: The 131I incorporation factor stated in the German incorporation guideline of 10-6 is disproportionally high. Following the evaluated urine samples, the 131I incorporation factor can be reduced by a factor of 10 to 10-7 for employees working on an 131I therapy ward independent of their profession. This will in most cases lead to more accurate calculations and may avoid time and cost intensive incorporation monitoring by the radiation protection authorities.

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