EFFECT OF MULTIPLE FACTORS ON SUCCESS RATE OF HIGH DOSE RADIOIODINE THERAPY (>150 CI/GR) IN 164 PATIENTS WITH HYPERTHYROIDISM

Background: Radiodine therapy (RIT) for hyperthyroidism is increasingly used as a therapy of choice in most of the patients. Effect of multiple factors on the result of therapy was noted. This study tries to analyze the effect of multiple factors on success rate of RIT. Methods and patients: One hundred and sixty four hyperthyroid patients referred for RIT therapy from 1996-99, were studied. Thyroid examination and 24 hrs RAIU were performed in all patients and 150-255 μCi/gr of ¹³¹I was administered. Follow up of the patients, including thyroid examination and thyroid values measurements were done at 2-6 months after treatment. The patients were divided in two groups: those who responded to radioiodine (group 1) and those who did not (group 2). Results: Two to six months after RIT, seventy one percent of the patients were in group 1 and 29% in group 2. No difference was noted in the mean age [45.7 yrs vs 47.2 yrs] (P=0.42), total Iodine dose [15.4 mCi vs 17.2] (P=0.2), Iodine dose per gram of thyroid weight [189.3 μCi/gr vs 192.6 μCi/gr] (P=0.06) and female/male ratio [65/21 vs 30/5] (P=0.32) between two groups. The mean thyroid weight was 59.1 gr in group 1 and 55.2 gr in group 2. Using logistic regression, the only significant effective factor in success of therapy was thyroid weight (R=0.172, P=0.03). With inceasing thyroid weight, success rate of Iodine therapy was decreased. Conclusion: With high dose (>150 μCi/gr) RIT, only thyroid weight negatively affects the result of the therapy and the other factors have no significant role.