Context: Radioiodine ablation of the thyroid remnant after thyroidectomy is commonly performed in the management of patients with differentiated thyroid cancer. While many centers administer an activity of 100 mCi, there is uncertainty over using a lower activity.

Objective: A systematic review of the published literature was used to compare the success rates of remnant ablation using about 30 mCi with around 100 mCi (1.1 vs. 3.7 GBq).

Data sources: Medline and Embase 1966 to March 2006.

Study selection: All studies that reported rates of successful ablation associated with about 30 or around 100 mCi of radioiodine.

Data extraction: Studies were based on reviews of patient case notes (n = 41), prospective cohorts (n = 12) and randomized trials (n = 6). We obtained the success of thyroid remnant ablation according to different administered activities of radioiodine. Where a study reported on two or more activities, the risk ratio of having a successful ablation (about 30 vs. around 100 mCi) was calculated and combined in a meta-analysis.

Data synthesis: Observational studies confirmed the high ablation success rate (approximately 80%) using around 100 mCi, though 22% of studies reported a rate 90%. The pooled ablation success rate in these studies was 10% lower using 30 mCi compared with 100 mCi (95% CI 3 to 17%, P = 0.01). The meta-analysis of the randomized trials produced equivocal results. For example, the rate of successful ablation in patients given 30 mCi was 8% lower compared with 100 mCi (95% CI 29% lower or up to 20% greater, P = 0.58), consistent with there being no difference or that 30 mCi is much less effective.

Conclusions: From the published data, it is not possible to reliably determine whether ablation success rates using 30 mCi are similar to using 100 mCi. Large randomized trials are needed to resolve the issue and guide clinical practice.