BACKGROUND
Radioactive iodine therapy is an important part of the treatment of advanced thyroid cancer. It works because the radioactive iodine is taken up and concentrated in thyroid cells, both normal and cancerous, and destroys these cells. Radioactive iodine is also taken up in the salivary glands but is not concentrated in the cells, minimizing any damage. However, inflammation of salivary glands, dryness in the mouth and consequently dental problems are known complications of radioactive iodine therapy that are seen in at least 10% of thyroid cancer patients treated with high dose radioactive iodine. Many agents have been studied in the past (lemon drops, sour candy, vitamin E and C, chewing gum, etc.) in order to preserve salivary gland function. Unfortunately, we still not have an effective treatment to protect salivary glands from the radiation. Selenium is a known antioxidant that has shown to decrease side effects of radiation therapy in other cancers. In this study the authors explore the role of selenium in preservation of salivary glands function after radioactive iodine therapy.

THE FULL ARTICLE TITLE:
Son H et al Effect of selenium supplementation for protection of salivary glands from iodine-131 radiation damage in patients with differentiated thyroid cancer. Hell J Nucl Med. 2017 Jan-Apr;20(1):62-70.

SUMMARY OF THE STUDY
A total of 16 patients with thyroid cancer undergoing their first radioactive iodine therapy were enrolled in the study. They were divided into two groups: 8 patients in the selenium group received selenium for 10 days, 3 days before and 6 days after radioactive iodine therapy, the other 8 patients in control group received a placebo. Patients were treated with 100-150 mCi of radioactive iodine. The authors measured amylase, a protein produced by salivary glands before, 2 days and 6 months after radioactive iodine therapy. Also salivary gland scintigraphy, a study measuring salivary gland ability to produce saliva, was done before and 6 months after radioactive iodine therapy. A questionnaire evaluating symptoms of salivary gland dysfunction were given before and 6 months after radioactive iodine therapy.

Results of the study showed significantly higher increase of serum amylase 2 days after radioactive iodine therapy in control group compared to selenium group that reflects more injury to salivary glands in the placebo group. Moreover, the results of salivary scintigraphy and scores on the questionnaire 6 months after radioactive iodine therapy were significantly different in the selenium and placebo groups reflecting that the long term damage of salivary glands was higher in control group.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study suggests that selenium supplementation during radioactive iodine therapy may be protective to salivary glands. Studies with larger number of patients are needed to further evaluate the clinical significance of changes in laboratory work up and imaging studies.

— Valentina Tarasova, MD

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