The use of delay tanks in the management of radioactive waste from thyroid therapy.

An underground system of tanks was installed to delay the discharge of 131I waste from the thyroid therapy unit to the on-site sewage treatment plant. As a consequence, the level of radioactivity discharged to sewage has fallen by a factor of 530, reducing the radiation dose to hospital and auxiliary service staff. Cancer patients are no longer required to collect their urine, hence increasing the hygiene for all concerned. A model was developed of iodine waste which estimates the dose rate above the delay tanks and the activity of iodine discharged. The maximum effective dose to a member of the public due to the holding tanks is 40 microSv.year-1. There is now better management of the radioactive waste from the iodine therapy ward.