Abstract

Background

The HiLo trial was the first randomised trial developed by the NCRI Thyroid Subgroup. It demonstrated that 6-9 month post-ablation success rates were similar between a low administered radioactive iodine (RAI) activity (1.1GBq) and the standard high activity (3.7GBq). International guidelines consequently recommended 1.1GBq in selected low risk patients, but there was a lack of long-term data. HiLo now has a median follow-up of 6.5 years, to examine recurrences.

Method

Patients were recruited 2007 to 2010, and randomized (multicentre factorial design) to 1.1 or 3.7GBq RAI, each with either Thyrogen or thyroid hormone withdrawal (THW), 1:1:1:1 ratio. Patients had annual clinic visits. Thyroid cancer recurrences were diagnosed and confirmed using standard methods: serum thyroglobulin, ultrasound, FNA cytology, RAI scans, CT and MRI.

Results

Among 434 patients with follow-up,there were 21 recurrences (11 and 10 with 1.1GBq and 3.7GBq respectively). The 3, 5 and 7 year recurrence rates were similar between 1.1GBq RAI (1.5, 2.1 and 5.9%), and 3.7GBq RAI (2.1, 2.7 and 7.3%); hazard ratio 1.10 (95%CI 0.47-2.59, p-value=0.83). 1.1GBq was not associated with noticeably more recurrences than 3.7GBq within T- and N-stage groups, even among T3 patients. Only one patient (T3 stage/N0 at baseline) died from thyroid cancer (1.1GBq). The recurrence rates at 3, 5 and 7 years were 1.5, 2.1 and 8.3% among patients using Thyrogen, similar to those using THW, 2.1, 2.7, and 5.0% (hazard ratio 1.62, 95%CI 0.67-3.91, p-value=0.28).

Conclusion

HiLo has the longest follow-up and more recurrences than any other randomised study. It shows that recurrence rates are similar in patients who had low or high dose RAI ablation, and also between those prepared for ablation using Thyrogen or THW. This is reassuring evidence on the long-term value of using a low administered dose in selected cases, and international guidelines can be updated now.