Study designs of evaluations included in the review
Randomised controlled trials (RCTs) and cohort studies were eligible for inclusion in the review. The authors also included a historical cohort of patients seen by one of the authors.
Specific interventions included in the review
Studies that compared a 1,110 (+ or - 185) megabecquerel (MBq) dose of I-131 with higher doses using a similar protocol were eligible for inclusion. In the majority of the included studies, the low dose used was 1,110 MBq (range: 925 to 1,258) and the most commonly used high dose was 3,700 MBq (range: over 1,110 to 3,700).
Participants included in the review
Studies of patients who had received surgery for differentiated thyroid cancer were eligible for inclusion in the review. Patients not eligible for inclusion were: patients with medullary, anaplastic or poorly differentiated carcinomas who were not given radioiodine; patients who presented with distant metastases; and patients who received their first dose of I-131 more than 12 months after surgery. The studies included patients who had received total, near-total and sub-total thyroidectomy.
Outcomes assessed in the review
Studies in which the relative risk of failure of remnant ablation associated with dose levels of I-131 could be calculated were eligible for inclusion. The studies had to have assessed the outcome after the first I-131 ablation post-surgery with clear criteria. The studies also had to have performed whole body scanning between 3 and 12 months after the therapeutic dose of I-131. The criteria for successful ablation used in the included studies varied; details were provided in the paper.
How were decisions on the relevance of primary studies made?
The two authors independently assessed studies for inclusion in the review. They did not state how any disagreements were resolved.