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

Abstract

Post-surgical therapeutic management of differentiated thyroid cancer (DTC) is still a controversial subject. Indeed, there is no consensus on the dose of 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.

Efficacy of Low-Dose Radioiodine Ablation in Low- and Intermediate-Risk Differentiated Thyroid Cancer: A Retrospective Comparative Analysis

“…Finally, we found that initial recurrence risk and a low-dose ablation were independent predictors for recurrence in our sample. These results are in contrast with those reported by HiLo, where recurrence rates were not associated with RAI ablation strategy [7,8], and also with the results of comparative analyses published to date [9,10]. In this point, it is also interesting to remark that when we took into account only patients with low-risk thyroid cancer, the RAI dose had no relation to recurrence risk, but when we analyzed only patients with intermediate-risk tumours, RAI dose was a strong predictor of recurrence, suggesting that low-dose ablation might be a better strategy in patients with low-risk thyroid cancer than in patients with intermediate-risk tumours.…”

“…We found that sTg at the moment of ablation was an independent risk factor for nonexcellent response in the complete sample, but also when we separated patients with low-an intermediate-risk tumours. These results are similar to the results reported by Ghachem et al [9], who found that patients with Tg after surgery <10 ng/mL were more likely to have a complete response, and Fallahi et al, who found that a Tg<4.5 ng/mL was predictive of a complete response [16]. Tg levels after surgery and in RAI ablation have been studied as factors affecting the response to treatment and recurrence rates by many authors [17][18][19][20], and our results seemed to be in the same direction.…”

“…The main difference of our study to HiLo was anti-TgAb consideration that was not described in this clinical trial, and with ESTIMABL1 the difference was the inclusion of intermediate-risk tumours. Nevertheless, the rate of excellent response in the low-dose group was 78.9%, and this result is comparable to previous studies [8,9,11,14,15].…”

“…In the HiLo study, they compared low-risk and intermediate-risk tumour recurrence rates with low (<100 mCi) and high doses (≥100 mCi) of RAI, showing a noninferior result (1-2% risk of recurrence at 5 years in both groups) [8]. Other authors, such as Ghachem [9], Schlumberger [14], Qi [15] or Jiménez-Londoño [11], have reported similar results in observational studies, concluding that low doses were noninferior to high doses in patients with low-risk thyroid cancer. In our study, we observed a higher rate of indeterminate responses in the group treated with low doses of RAI and a higher rate of excellent and incomplete biochemical responses in the group of high-dose ablation, with statistical significance.…”

“…Despite the results of ESTIMABL1 and HiLo suggesting that low-dose RAI ablation is effective in patients with low-and intermediate-risk thyroid cancer, and many subsequent papers supporting this idea [9][10][11], there is no international consensus on RAI dose. In fact, the European Association of Nuclear Medicine and the Society of Nuclear Medicine and Molecular Imaging refused to endorse the ATA 2015 guidelines.…”