Background: Personalized recurrence risk ideally guides treatment with radioactive iodine (RAI) in differentiated thyroid cancer. 2015 ATA guidelines provide some risk stratification to aid treatment decisions but is not comprehensive. The aim of our study was to develop an algorithm for RAI treatment based upon personalized recurrence risk calculated using ATA risk features combined with histological extra-thyroidal extension (ETE) and post-operative serum thyroglobulin (sTg).
Methods: Retrospective multivariable analysis of 1117 patients who received RAI following thyroidectomy at a quaternary centre in Australia between 2008-2018, with a sTg (TSH > 30mIU/L). Prospectively collected data included age, gender, histology and AJCC staging. ATA risk was calculated retrospectively.
Results: In intermediate and high ATA risk there was no difference in risk of recurrence between 4GBq or 6 GBq activity of RAI (p = 0.10). Independent of ATA risk, patients with a sTg > 10ug/L had a worse progression free survival (PFS) than those with sTg < 10ug/L (p < 0.001). ETE stratified by 4 histological categories was significantly associated with PFS (p < 0.001). On multivariate analysis gross ETE, sTg > 10 ug/L, multifocal papillary thyroid cancer (PTC), follicular variant PTC and follicular thyroid cancer were associated with synchronous metastasis. Our algorithm, with 5 recommended activities was validated on 218 patients treated with RAI in 2017-2018 correctly recommending RAI activities for patients in ATA low and high risk groups and for those with synchronous metastasis.
Conclusions Our algorithm extends ATA risk stratification by including sTg and ETE which we found to be independent predictors of recurrence and synchronous metastasis in DTC. We have developed an online RAI decision support tool to provide evidence based treatment guidelines, reducing unnecessary RAI treatments while confidently treating patients with high risk of metastatic disease.