The thyroid is a butterfly-shaped gland in the neck that secretes thyroid hormones which regulate a number of physiologic processes, including growth, development and metabolism. With respect to Ionising Radiation, the thyroid is vulnerable to intakes of radioactive Iodine -125 by either Inhalation or Ingestion. In the event that an intake of I-125 occurs the thyroid will be the organ or accumulation and will preferentially uptake the iodine from the systemic system. This creates an Internal Radiation hazard.