Background: Radioactive iodine (RAI) is often used in patients with thyroid cancer, however the optimal dosage of RAI has yet to be established. Adjuvant RAI reduces recurrence in moderate-high risk thyroid cancer [1]. In low risk disease, RAI is often employed to ablate remnant thyroid tissue. Changes to clinical practice over the past decade, influenced by the release of HiLO and ESTIMABLI studies in 2012 and ATA guidelines in 2015([1-3], have seen a shift to lower doses of RAI.
Method: Retrospective analysis of 1348 patients who received RAI at a quaternary centre in Australia between 2008 and 2018. Prospectively collected data included age, gender, histology, and AJCC stage (7th ed). ATA risk was calculated retrospectively. Statistical analyses were conducted using Statistical Package for Social Sciences ( SPSS) version 26 (SPSS Inc IL, USA).
Results: The median dose of RAI decreased from 4.21 GBq in 2008 to 3.9 GBq in 2018 (<0.0001). The principal driver of this change was an increased use of 1GBq dose from 1.2% in 2008-2011 to 20.4% in 2017-2018. In binomial regression analysis, factors significantly associated with low dose RAI (<1.3 GBq) were females (OR 1.67, p=0.037 [CI 1.03-2.72]), low ATA risk (OR 6.61, p <0.001 [CI 2.2.66- 16.39]) and stage 1 AJCC (OR 4.84, p=0.004 [CI 1.64-14.31]). Confining the analysis to 2017-2018, only low ATA risk (OR 6.82, p=0.007 [1.70-27.36]) were associated with use of low RAI dose. For patients assessed as low risk of recurrence by ATA criteria in 2017-2018, 42.3% received a low dose with a median dose of 1.95GBq.
Conclusions: RAI doses have significantly reduced over the past decade at our institution. Nevertheless, some patients assessed as low risk of recurrence by ATA criteria are still receiving high doses of RAI.