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It is well known that a considerable amount of radioiodine is exhaled after radioiodine therapy (RIT) leading to unwanted radiation exposure through inhalation for non-involved persons. This study focuses on the amount of exhalation in the breath-out air of RIT-patients and the dosimetric consequences. Furthermore, the correlation between radioiodine uptake and exhalation was investigated. The radioiodine species were collected in a filter system and quantified over time by measurements with a scintillation counter. The dosimetric implications were then studied for different exposure scenarios. Of the activity administered to the patient, approximately 10 -3 % (50-110 ppm) is exhaled. The radioiodine inhalation taking place following exhalation in the vicinity yields doses of up to 500 μSv (children, staying with the patient immediately after application and for the next 8 h). Three days after administration the doses are significantly reduced. This study lays emphasis on previous assumptions that exhalation depends on thyroid storage. Regardless of the type of thyroid disease, the predominant form exhaled is organic radioiodine. The amount of exhaled radioiodine is small but from the point of view of radiation protection, by no means negligible immediately after administration. Radiation doses received by incorporation of exhaled radioiodine can easily exceed 100 μSv soon after administration of radioiodine. Three days after RIT the radioactivity can still be measured in the exhaled air but even at maximum, the annual doses lie far below 10 μSv and are thus comparatively low., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Procedures to determine the release of hazardous gaseous substances including radioactive iodine are covered by different norms such as the European standard EN 14175 and the German national standard DIN 25466. The detection of sulphur hexafluoride (SF 6 ) is required to comply with the prescribed methodology. The detection limit of this test is 4.5·10 -7  mol/m 3 in exhaust air. This detection limit would represent a very high activity in the region of 0.27 TBq/m 3 leading to an unacceptable risk. We therefore developed a test using a filter system, consisting of a combination of filters capable of separating various chemical forms of airborne radioiodine. Air samples were collected directly in front of the fume hood and in the laboratory beside two different fume hoods of a similar construction with a final activated carbon filter for retention of radioiodine. Particular attention was therefore paid to air samples taken after passage over the filters. Significant differences in the degree of retention of iodine were found between the two fume hoods investigated. In one test a malfunction of the fume hood was demonstrated. In this case 0.148 × 10 -3 % of the total released activity per m 3 air was found 1 cm in front of the hood sash. A remarkably high fraction of the activity released in the fume hood (1.3 × 10 -3 %/m 3  air) was measured after the activated carbon filter. In the ambient air, values of up to 8.6 × 10 -6 % pro m 3 laboratory air sampled were measured, despite a 6-8-fold air exchange. The selected procedure is a factor of 10 11 (Schomäcker et al., 2001) more sensitive than the standard recommended methods (EN 14175). The standard test prescribed by the DIN/EN failed to reveal any inadequacy in the protective function of the radionuclide hood with respect to radioiodine retention., (Copyright © 2016 Elsevier Ltd. All rights reserved.)