Low-dose Radioiodine as Effective as High-dose in Thyroid Ablation

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Two studies in The New England Journal of Medicine found that low-dose radioiodine is as effective as a high-dose strategy in treating patients with thyroid cancer and that recombinant human thyrotropin (thyrotropin alfa [Thyrogen]) and thyroid hormone withdrawal had similar efficacy in preparing patients for radioablation. In both studies, thyrotropin alfa was administered by intramuscular injection of 0.9 mg on 2 consecutive days; the low dose of radioiodine was 1.1 GBq and the high dose was 3.7 GBq.

A randomized noninferiority trial conducted at 29 centers in the United Kingdom and funded by Cancer Research UK compared low-dose and high-dose radioiodine, each in combination with either thyrotropin alfa or thyroid hormone withdrawal before ablation, in patients with tumor stage T1 to T3 differentiated thyroid cancer and possible spread to nearby lymph nodes but without metastasis.

Among 421 evaluable patients, “success rates were 85.0% in the group receiving low-dose radioiodine vs 88.9% in the group receiving the high dose, and 87.1% in the thyrotropin alfa group vs 86.7% in the group undergoing thyroid hormone withdrawal,” the authors reported. “Similar results were found for low-dose radioiodine plus thyrotropin alfa (84.3%) vs high-dose radioiodine plus thyroid hormone withdrawal (87.6%) or high-dose radioiodine plus thyrotropin alfa (90.2%),” they added.

Important Advantages

“The use of a reduced dose of radioiodine has important advantages. Patients, many of whom are women with children, would spend less time in hospital isolation and have fewer side effects,” the authors noted. In this study, fewer patients in the low-dose group were hospitalized for at least 3 days—13% compared with 36.3% for the high-dose group (P < .001). “The proportions of patients with adverse events were 21% in the low-dose group vs 33% in the high-dose group (P = .007) and 23% in the thyrotropin alfa group vs 30% in the group undergoing thyroid hormone withdrawal (P = .11),” they reported.

The authors concluded, “Our study answers two central questions involving radioiodine ablation of thyroid remnants after surgery for differentiated thyroid cancer: namely, that the efficacy of low-dose radioiodine is similar to that of high-dose radioiodine, and that the efficacy of low-dose radioiodine ablation is not compromised by the use of thyrotropin alfa instead of thyroid hormone withdrawal.”

Similar Study

They noted that the study conducted at 24 centers in France was similar to their study, but excluded patients with stage T3 tumors or stage T2 tumors with lymph node involvement. The study funded by the French National Cancer Institute and the French Ministry of Health also found equivalent ablation rates with low-dose and high-dose radioiodine and the use of thyroid hormone withdrawal or recombinant human thyrotropin.

“For the 684 patients who could be evaluated, a follow-up study was performed between 6 and 10 months (average, 8.3±1.6 months) after 131I administration; there were no significant differences in the time after 131I administration in the four groups receiving treatment (two 1.1-GBq groups and two 3.7-GBq groups),” the researchers wrote. “On the basis of the local thyroglobulin determinations, thyroid ablation was considered complete in 631 (92%) of the 684 patients,” they stated.

“This study shows similar rates of thyroid-remnant ablation among patients with thyroid cancer, without evidence of residual disease after surgery, when either 1.1-GBq or 3.7-GBq 131I is used and when the patient is prepared by means of either recombinant human thyrotropin or withholding of thyroid hormone,” the authors summarized. “A similar ongoing study reached the same conclusions. Thus, the use of recombinant human thyrotropin and a low dose of 131I for postoperative radioiodine ablation represents an effective and attractive option for the management of low-risk thyroid cancer that reduces the amount of whole-body irradiation and maintains the quality of life. Future randomized studies in patients with low-risk thyroid cancer should be permitted to restrict radioablation to patients in whom it is beneficial.” ■

Schlumberger M, et al: N Engl J Med 366:1663-1673, 2012.

Mallick U, et al: N Engl J Med 366:1674-1685, 2012.