131Iodine release from thyroid carcinoma therapy units. Suggestions for improving environmental protection and economy

Therapy of thyroid carcinoma is related to I-131 release into the environment. Investigating all relevant pathways of activity release inside and outside of a therapy unit, it was shown up that beside fecal water a relatively high amount of therapy activity was released by the wash-water. The air is contaminated with activity as well, however, the total released activity is markedly lower compared to the fecal water. Filter systems are recommended when the release pathways are relatively short. The patient himself releases after discharge from the therapy unit a significant part of activity. Hitherto, patients are discharged with a borderline activity retention of 74 MBq (2 mCi). This is not useful in carcinoma patients with an effective half-life lower than 2 days, these patients should remain in the therapy unit until they have a residual activity of 37 MBq (1 mCi). From the view of ecology and economy, therefor it is not useful to construct expensive activity retention units for fecal water in order to achieve extremely low activity release on this path: all release pathways have to be evaluated integrally with inserting the financial facilities most efficiently according to the ''ALARA'' principle. Patients with a low effective half-life and high activity release rate should stay longer in the therapy unit. These thyroid carcinoma patients should get the therapy in large therapy units, whereas smaller nuclear medical departments should concentrate on low-dose therapies in hyperthyroid function anomalies. (orig.)