The AEC/NRC 30 mCi rule: regulatory origins and clinical consequences for 131I remnant ablative doses

Clinical and historical uncertainty exists surrounding the regulations of the Atomic Energy Commission/Nuclear Regulatory Commission (AEC/NRC) requiring patient hospitalization when (131)I activities exceed 30 mCi. This review investigates the sometimes disturbing regulatory and clinical origins and consequences of the use of this low, 30 mCi dose as a prescription for thyroid remnant ablation.

As early as in the 1940s, activities of (131)I between 30 and 200 mCi, often fractionated, were employed. The AEC deliberated from 1947 to the early 1960s before imposing as a license condition the requirement of hospitalizing patients until they contained <30 mCi of any byproduct material. The written AEC record throughout these years contains no supportive data to suggest safety issues requiring hospitalization at this activity level of (131)I. Yet the techniques for making the necessary calculations for determining radiation safety were available at this time. Declarations on the subject by nongovernmental bodies were misinterpreted as confirming such hospitalization as a legal requirement. The 30 mCi license condition was codified into NRC regulations in 1987 and was subsequently removed in 1997. Without any data, these U.S. regulatory agencies caused significant expense, inconvenience, and fear, affecting thyroid cancer patients and their families. This 30 mCi regulatory activity limit morphed, by a fortunate coincidence, into an acceptable ablative activity before there were solid confirmatory data. Studies on this 30 mCi ablative dose indicate that this activity was never associated with radiation health and safety issues, and was never more effective than higher ablative doses but led slightly more often to the need for a second (131)I dose. Nevertheless, the available data generally support the American Thyroid Association and Society of Nuclear Medicine and Molecular Imaging Guidelines, which indicate, without a treatment activity preference, that 30-100 mCi of (131)I provide adequate ablation. Follow-up data on the rates of recurrences, deaths, and second primary malignancies within this range of doses are unavailable.

This history of unjustified governmental action and blind acceptance must remind the medical/radiation safety community to require solid data before ever again adopting baseless requirements. The 30 mCi dose should have never been employed as a requirement for hospitalization.