A comparison of low versus high radioiodine administered activity in patients with low-risk differentiated thyroid cancer

Post-surgical therapeutic management of differentiated thyroid cancer (DTC) is still a controversial subject. Indeed, there is no consensus on the dose of 131 I to be administered, although the current trend towards therapy easing through mini-cures for patients with good prognosis. To confirm the non-inferiority in terms of effectiveness of an ablative mini-cure from 1.11 to 1.85 GBq, over a cure of 3.7 GBq, in patients with DTC operated for low and very low risk. We retrospectively studied 157 patients with very low and low risk DTC, followed in the Nuclear Medicine Department of the Salah Azaiez Institute between 2002 and 2012. These patients had a complementary radioiodine therapy with either low dose (group A) or high dose (group B) with an evaluation at 6 months post treatment and in long-term. The study took place at a referral center. The average age was 42.8 +/- 13.7 years with a female predominance (86.7 %). The DTC papillary represented the most common etiology (95 %) with a predominance of pure papillary (68 %) on the follicular variant (27 %). The first cure evaluation did not show statistically significant difference between the two approaches in terms of therapeutic ablative efficiency (p = 0.13). The overall success rate was 77 % (121/157), with 83 % (54/65) in group A and 72.8 % (67/92) in group B. The likelihood of having a remission from the first cure was 1.83 times greater for patients treated with low doses (OR = 1.83, 95 % CI 0.23-1.29). At the end of follow, we have noted one case of refractory disease. The male gender (adjusted OR = 2.71, 95 % CI 0.51-4.23, p = 0.03), and the baseline Tg >= 10 (ng/ml) (adjusted OR = 3.48, 95 % CI 1.25-9.67, p = 0.01) were significantly independent predictors of successful first cure ablation. The results provide that mini-dose protocol is not less effective for ablation of the thyroid remnant than 3.7 GBq activity.