PARIS – Low-dose radioiodine ablation of 1.1 gigabecquerels (GBqs) is just as effective as the standard 3.7 GBq dose in eradicating thyroid remnants, with or without the concomitant use of recombinant human thyroid-stimulating hormone, in patients who have undergone thyroidectomy for differentiated thyroid cancer.

Two international randomized, controlled trials presented Sept. 13 at the International Thyroid Congress reached the same conclusion: Ablation rates were virtually identical between the two radioiodine doses. The findings should “change medical practice in the [United States], and around the world,” said Dr. Ernest Mazzaferri, professor emeritus of medicine at Ohio State University, Columbus.

“Today, we learned of two studies that will change the impact of how this disease is treated, by using very small amounts of radiation,” he said in an interview. “These robust studies will change practice – as they should – and are a strong argument to treat with a low amount of radiation. It’s better for the patients, and it works.”

The two trials, ESTIMABL from France and the British HiLo trial, encompassed almost 1,200 patients with differentiated thyroid cancer who had undergone a complete thyroidectomy and were ready for radioiodine ablation. Both were multifactorial studies that compared the 1.1- and 3.7-GBq doses with and without the use of recombinant human thyroid stimulating hormone.

Dr. Bogdan Catargi of the Centre Hospitalier Universities, Bordeaux, presented the ESTIMABL results. The phase III study randomized 753 patients to four strategies for postoperative radioiodine ablation in a multifactorial design: a method of thyroid stimulating (TSH) stimulation (either thyroid hormone withdrawal or continuation) and a method of radioiodine ablation (1.1 GBq or 3.7 GBq). Full follow-up data were available for 542 of the group.

The patients were a mean of 49 years old; they had undergone total thyroidectomy for differentiated papillary or follicular thyroid cancer 1-3 months prior. Most (90%) had papillary cancer. Patients with aggressive histology were not included in the trial.

Thyroid ablation was determined 6-10 months after treatment with recombinant human thyroid stimulating hormone (rhTSH), stimulated thyroglobulin, and neck ultrasound.

At final follow-up, ablation rates were not significantly different among any of the four groups. In the group retaining rhTSH and treated with 1.1 GBq, the rate was 89%; in those on rhTSH treated at 3.7 GBq, the ablation rate was 89%. Among those treated with the low dose whose rhTSH was withdrawn, ablation was complete in 92%. The rate of ablation was 93% in that group treated with the higher-radiation dose.

None of the between-group differences were significant, Dr. Catargi said. “When comparing the four groups, we saw no difference between them in terms of either the stimulation method or radioiodine dose,” he said. “This is a major finding, showing for the first time the equivalence of these four strategies.”

If the finding holds up in the final analysis, “It validates the use of recombinant TSH and low radioiodine for these low-risk patients,” he said.

Dr. Ujjal K. Mallick of the Freeman Hospital, Newcastle upon Tyne, U.K., presented the HiLo trial results. Similar in design to ESTIMABL, this study randomized 438 patients who had undergone thyroidectomy to either 1.1 GBq or 3.7 GBq and either rhTSH or thyroid hormone withdrawal. Dr. Mallick presented preliminary data on 258 patients who had completed the 9-month follow-up period.

All patients were put on a low-iodine diet and had a pre-ablation scan to assess remnant size. Ablation success was determined 6-9 months later using an I-131 iodide diagnostic scan.

Again, Dr. Mallick said, all of the treatment combinations were similarly effective. Ablation rates ranged from 93% to 95%. Subgroup analyses also found no difference between withdrawing or continuing rhTSH, and radioiodine dose. There were also no significant differences when the group was examined by tumor stage or nodal involvement. “The conclusion we can draw is that 1.1 GBq with rhTSH has a similar ablation rate to rhTSh withdrawal with the 3.7 GBq radioiodine,” he said.

HiLo also examined quality of life in its patients and found that patients who had the lower radioiodine dosage left the hospital earlier and missed fewer days of work, “raising the idea that this can be a single-day procedure,” Dr. Mallick said. Patients who stayed on their thyroid hormone, however, felt better and were able to accomplish more at home and at work than were those whose hormone was withdrawn.

“We can now say that patients with thyroid cancer staged at T1-T3 and favorable histology can be as successfully treated with 1.1 GBq as they can with 3.7, and that rhTSH continuation or withdrawal does not affect ablation.”

HiLo was sponsored by Cancer Research U.K.; Dr. Mallick disclosed that he is a consultant for Genzyme Corp., which provided the rhTSH for the study. ESTIMABL was funded by the French Institute National du Cancer; Dr. Catargi did not mention any financial disclosures.

Low-Dose Radioiodine as Effective as Higher Doses in Thyroid Remnant Ablation