Because iodine accumulates in the thyroid, radioactive iodine-131 can be used to kill cancerous thyroid tissue with minimal damage to other tissue. Sometimes the dose is administered in an outpatient setting and the patient is allowed to go home, with instructions on how to protect others from radiation exposure. Ninety-five days after treatment, what percentage of the initial iodine-131 in the thyroid remains, ignoring the relatively small amount that is excreted?