Tiny “seeds” containing radioactive iodine are often implanted in the prostate gland to treat cancer. Now, findings from a case report indicate that these seeds can break open and release the iodine, which is then absorbed by the thyroid gland, a key regulator of metabolism.

Dr. Qin-Sheng Chen of the Cleveland Clinic Foundation, Mayfield Heights, Ohio, and colleagues describe the patient in a report published in the Journal of Urology.

The case patient’s thyroid absorption was too low to be clinically important, Chen told Reuters Health. Nevertheless, “since more and more prostate cancer patients will be treated” with this type of treatment, known as brachytherapy, increased rates of thyroid absorption are expected.

Chen and Dr. Henry F. Blair came across this case while performing routine tests to look for seed migration. Since late 2001, a total of 246 patients were evaluated and 23,184 seeds were implanted. Of these, 75 seeds were released in the urine and 25 migrated to the chest.

In the current case, however, the seeds did not seem to move to another location in the body, rather they simply became damaged in the prostate and released the iodine into the blood. The iodine then traveled to the thyroid gland.

No other occurrences have been identified, but “in cases where the radiation dose to the thyroid is found to be significant, preventive medication - such as iodine solution - would be given to minimize possible complications,” Chen said. By giving iodine solution, the thyroid gland is less likely to absorb the radioactive iodine released from the damaged seed.

SOURCE: Journal of Urology, November 2004.