Dehbi HM, et al. - Researchers compared recurrence rates between radioactive iodine doses in HiLo, a large randomised trial of patients with well-differentiated thyroid cancer reported in 2012 with results demonstrating similar post-ablation success rates at 6–9 months between a low administered radioactive iodine (131I) dose (1·1 GBq) and the standard high dose (3·7 GBq). In line with data from large, recent observational studies, no higher recurrence rate were observed among patients who had 1·1 GBq radioactive iodine ablation compared to that for 3·7 GBq in this study. Findings support the use of low-dose radioactive iodine for treatment of patients with low-risk differentiated thyroid cancer. In addition, use of rhTSH did not effect recurrence risk.

Methods

• A non-inferiority, parallel, open-label, randomised controlled factorial trial, HiLo, was carried out at 29 centres in the UK.
• Patients aged 16–80 years with histological confirmation of differentiated thyroid cancer requiring radioactive iodine ablation (performance status 0–2, tumour stage T1–T3 with the possibility of lymph-node involvement but no distant metastasis and no microscopic residual disease, and one-stage or two-stage total thyroidectomy) were considered eligible to be included.
• Random assignment of patients (1:1:1:1) to 1·1 GBq or 3·7 GBq ablation, each prepared with either recombinant human thyroid-stimulating hormone (rhTSH) or thyroid hormone withdrawal, was done.
• At annual clinic visits, patients were followed-up.
• Using a combination of established methods according to national standards, recurrences were diagnosed at each hospital.
• Researchers used Kaplan-Meier curves and hazard ratios (HRs) for time to first recurrence, which was a pre-planned secondary outcome.

Results

• Random assignment was performed on 438 patients between Jan 16, 2007, and July 1, 2010.
• A median follow-up of 6·5 years (IQR 4·5–7·6) was performed in 434 patients (217 in the low-dose group and 217 in the high-dose group), which ended in Dec 31, 2017.
• Twenty one patients had confirmed recurrences: 11 who had 1·1 GBq ablation and ten who had 3·7 GBq ablation.
• Four of these (two in each group) were considered to be persistent disease.
• Low-dose vs high-dose radioactive iodine groups showed similar cumulative recurrence rates (3 years, 1·5% vs 2·1%; 5 years, 2·1% vs 2·7%; and 7 years, 5·9% vs 7·3%; HR 1·10 [95% CI 0·47–2·59]; p=0·83).
• For T3 or N1 disease, no material difference in risk was observed.
• Among patients who were prepared for ablation with rhTSH and those prepared with thyroid hormone withdrawal, similar recurrence rates were seen (3 years, 1·5% vs 2·1%; 5 years, 2·1% vs 2·7%; and 7 years, 8·3% vs 5·0%; HR 1·62 [95% CI 0·67–3·91]; p=0·28).
• During follow-up, data on adverse events were not collected.