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¹³¹I Activity for Remnant Ablation in Patients with Differentiated Thyroid Cancer: A Systematic Review

Cancer Research UK & UCL Cancer Trials Centre (A.H.), University College London, London NW1 2ND, United Kingdom; Formerly Thyroid Cancer Unit (C.H.), Royal Marsden Hospital, London SW3 6JJ, United Kingdom; Newcastle General Hospital (U.M.), Newcastle NE4 6BE, United Kingdom; Chelsea and Westminster Hospital (M.H.), London SW10 9NH, United Kingdom; and Division of Medical Sciences (J.A.F.), University of Birmingham, Queen Elizabeth Hospital, Birmingham B15 2TH, United Kingdom

Address all correspondence and requests for reprints to: Allan Hackshaw, Deputy Director, Senior Lecturer in Epidemiology & Medical Statistics, Cancer Research UK & UCL Cancer Trials Centre, University College London, Stephenson House, 158-160 North Gower Street, London NW1 2ND, United Kingdom. E-mail: ah{at}ctc.ucl.ac.uk.

Context: Radioiodine ablation of the thyroid remnant after thyroidectomy is commonly performed in the management of patients with differentiated thyroid cancer. Although 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 approximately 30 mCi with approximately 100 mCi (1.1 vs. 3.7 GBq).

Data Sources: Data were obtained from MEDLINE and EMBASE for the years 1966 to March 2006.

Study Selection: All studies that reported rates of successful ablation associated with approximately 30 or approximately 100 mCi of radioiodine were reviewed.

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 (30 vs. 100 mCi) was calculated and combined in a meta-analysis.

Data Synthesis: Observational studies confirmed the high ablation success rate (80%) using approximately 100 mCi, although 22% of studies reported a rate of 90% or greater. The pooled ablation success rate in these studies was 10% lower using 30 mCi compared with 100 mCi (95% confidence interval, 3–17%; 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% confidence interval, 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.

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