Disposal of therapeutic 131I waste using a multiple holding tank system.

Therapeutic application of 131I for the treatment of thyroid cancer generates a significant amount of liquid radioactive waste. Discharge of this waste into the public sewage system is governed by local regulations. In Canada, the permissible concentration is such that only a few patients can be treated in modern water-efficient buildings if this waste is discharged directly through the toilet to the public sewage system. If the toilet discharge is first collected into a holding tank for physical decay before it is released, a large patient load can be handled without exceeding the permissible concentration. In this paper, the principles of operation and the design parameters are discussed, and a multiple holding tank system installed in the Princess Margaret Hospital/Ontario Cancer Institute is described.