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

AIMS To compare the efficacy of remnant ablation following a single low dose (specific activity of I-131 administered, 1074-1110 MBq) vs. a single high dose (mostly 2775-3700 MBq) of I-131 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 I-131 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 I-131 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 I-131 (2775-3700MBq) for ablation of the remnant.