Transient cytotoxicity of 131I beta radiation in hyperthyroid patients treated with radioactive iodine

BACKGROUND & OBJECTIVES Radioiodine ( 131 I) or radioactive iodine in low doses is used worldwide as the first line of management in the treatment of hyperthyroidism. Information is available on the extent and severity of cell damage after a high dose radioiodine ( 131 I) therapy for thyroid cancer, but information is scanty on its cellular effects, its extent and severity of cell damage after a low dose 131 I therapy. The present investigation was aimed to study the cytotoxic effects of a low dose 131 I therapy in varying doses as is normally being used in routine clinical practice in the treatment of various forms of hyperthyroidism. METHODS Peripheral blood lymphocytes were analyzed in 32 hyperthyroid patients. All of them received 131 I in the form of sodium iodide solution orally. Blood lymphocytes were studied for the presence of chromosomal aberrations (CA) and micro nucleus (MN) using micronucleus assay. Blood samples of these patients were drawn prior to the treatment, on 7 th and 30 th days after the treatment. RESULTS The results indicated a positive relationship between 131 I dose, CA and MN frequency. A statistically significant increase in CA and MN frequency in day 7 post- therapy and a decrease in mean levels of CA and MN on day 30 post-therapy were observed when compared to pre-therapy. INTERPRETATION & CONCLUSIONS This study showed that the cytogenetic damage induced by 131 I in low doses i.e., less than 555MBq was minimal and reversible. Patients can be motivated to undertake this safe and easy procedure as a first line of therapy in the treatment of hyperthyroidism.