Large-body radiation doses following radioiodine therapy.

In accordance with the recommendations of the International Radiological Protection Commission, the current maximum acceptable radiation dose limits for members of the public have been reduced to 1 mSv in the United States, Canada, and European Union countries including the United Kingdom. This has had a significant impact on radiation protection guidelines for contacts of patients treated with 131I. Many previous recommendations have relied upon models which may overestimate dose rates at short distances. We therefore undertook measurements of 131I dose rates using adult and infant phantoms that more accurately reflected true geometry. Effective dose calculations and patient contact restrictions were then derived from these direct dose measurements. Doses received by the adult phantom were measured at three distances (contact, 1.0 m, 2.0 m) and doses received by the infant phantom were measured at contact in two orientations (adult cradling infant over shoulder and at waist). The doses measured were significantly lower than previously predicted for the adult and infant phantom. Our measurements suggest that patient contact restrictions could be made less stringent than those currently in widespread use.