Exhalation of I-131 after radioiodine therapy: time dependence and chemical form

Aim: The change of both amount and chemical forms of radioiodine exhaled in the air of rooms with patients on the therapy ward should be investigated depending on radioactivity applied, time after application, and kind of thy roid disease. Methods: The air of word-rooms of 62 patients with thyroid ca rcinoma, Graves' Disease, and autonomy which received different therapy dos es, was investigated with on portable constant air flow sampler. Different chemical iodine species (organic, elemental, aerosol bound) were collected during 8 hr in various filters until 3 days after application of the radioi odine capsule, according to their chemical form. The radioactivity in the f ilters was measured with a well counter on defined time points after applic ation. Results: The radioactivity exhaled was between 0,008 and 0,03% relat ed to activity of radioiodine applied. The percentage of radioiodine exhale d related to the activity applied, differed significantly depending on dise ase and changed as follows. Grave's Disease > autonomy > carcinoma. The exh alation of radioiodine become stronger with increasing applied activities a nd showed on exponential decrease with time. The most part of radioiodine w as present in organic bound form. This organic portion decreased with time in favour of the other iodine species. Conclusion: The degree of accumulati on of radioiodine orally applied within thyroid seems to be in direct propo rtion to the extend of its exhalation. Further measurements directly in the breathing air of RIT-patients ore necessary, in order to clarify the relat ionship between degree of thyroid uptake and quantity as well as chemical f orm of radioiodine exhaled.