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I-131 Treatment for Hyperthyroidism

Anatomy of the thyroid and parathyroid glands; drawing shows the thyroid gland at the base of the throat near the trachea. An inset shows the front and back views. The front view shows that the thyroid is shaped like a butterfly, with the right lobe and left lobe connected by a thin piece of tissue called the isthmus. The back view shows the four pea-sized parathyroid glands. The larynx is also shown.

NCI study finds long-term increased risk of cancer death following common treatment for hyperthyroid

Radioactive iodine (RAI) treatment for hyperthyroidism is associated with increased risk of death from solid cancers, including breast cancer, new study finds.

Investigators in the Radiation Epidemiology Branch conducted a cohort study of 35,573 patients treated for hyperthyroidism from 1946 to 1964 to determine whether iodine (131I) treatment was associated with elevated risk of all-cause and cause-specific cancer mortality in a dose-dependent manner. 

They found that higher 131I administered and organ-absorbed doses were associated with increased risk of total solid cancer deaths, including deaths from female breast cancer.

To reconstruct the organ-absorbed doses due to oral administration of 131I, REB dosimetrists developed a new biokinetic model for iodine specific to patients with hyperthyroidism. Parameters of the model were obtained from results of measurements of iodine in blood, urine, and the thyroid following 131I treatments  for 3,138 patients. For these patients with available measured data, the individual organ doses were calculated based on the administered activity of 131I and the predictions of the amounts of iodide and protein-bound-iodine present in each organ and tissue, as well as the biological behavior of iodine in the body. These methods and the estimates of organ doses to all cohort members were described in a 2015 publication by Melo et al.

For more information, contact Cari Kitahara.

Radiation Epidemiology Branch - Research Areas

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