Radioactive iodine (radiolodine) is given to patients with some forms of thyroid cancer in order to destroy the cancer cells. 1311 has a half-life of 8 days. Women who have been treated with 1311 are
advised to not become pregnant for 180 days (approximately 6 months) to avoid the radioactive
contamination of a developing fetus.
If a woman has been given a dose of 10 mci (millicurie, a measurement of radiation), how much 1311
will still be in her system when she can safely become pregnant?
3.125% of the original isotope
22.5 x 10-6 mci
1.7 x 10-6 mci
There will be no iodine-131 left in her system after 180 days.