Ablation of the thyroid remnant and 131 I dose in differentiated thyroid cancer

AIMS To compare the efficacy of remnant ablation following a single low dose (specific activity of 131 I administered, 1074–1110 MBq) vs . a single high dose (mostly 2775–3700 MBq) of 131 I in patients with differentiated thyroid cancer and to determine whether or not the extent of surgery influences outcome. METHODS Nineteen studies have reported the results of low dose 131 I ablation. Of these, 11 met our criteria for a comparative analysis. Two additional cohorts of ours were added and these were analysed in two groups based on the extent of surgery (near‐total [NT; Woodhouse1] vs . sub‐total [ST; Woodhouse2]). There were 518 low dose and 449 high dose patients in all. RESULTS The average failure of a single low dose was 46 ± 28% (SD). Meta‐analysis revealed a statistically significant advantage for a single high over a single low dose and a pooled reduction in relative risk of failure of the high dose of about 27% ( P  < 0.01). From this we estimate that for every seven patients treated one more would be ablated given a high rather than a low dose (assuming a low dose failure risk of 50%). Also, a significantly greater proportion of patients are ablated after a single high or low dose, if they underwent near‐total as opposed to sub‐total thyroidectomy (summary relative risk (RR) 1.4; P  < 0.05). CONCLUSION High dose 131 I is more efficient than low dose for remnant ablation particularly after less than total thyroidectomy. Results suggest that patients with differentiated thyroid cancer should routinely have a total thyroidectomy followed by high dose 131 I (2775–3700MBq) for ablation of the remnant.