Introduction
Recent changes to recommendations regarding radioactive-iodine (RAI) therapy for thyroid cancer represent a significant shift in clinical practice. Studies indicate that low-dose RAI is as effective as high-dose for remnant ablation[1,2]. We reviewed the practice at our institution and its consistency with guidelines, and the factors influencing clinician decision-making around RAI dose.
Methods
A retrospective audit was conducted of adult patients in our institution. Participants had thyroid cancer (any variant), with initial RAI ablation between 29/08/2014–21/04/2017. Exclusion criteria included patients with irretrievable histology, or with metastatic disease without primary cancer in the thyroid. Patients received either low-dose (≤60mCi) or high-dose (>60mCi) RAI; most dose recommendations were made in a specialised clinic or by multidisciplinary consensus.
Chi-squared tests and logistical regression were used, with a significance cut-off of p=0.01.
Results
112 patients were eligible. 35% received low-dose RAI; 65% received high-dose. High dose was associated with increasing MACIS score. Every 1 increase in MACIS increased the likelihood of receiving high-dose RAI 1.68 times (Chi2=13.49 with 1df; p=<0.001). American Thyroid Association (ATA) score was also correlated (OR=4.68, Chi2=11.46 with 1df; p=0.001).
RAI dose was not correlated with age above/below 45 (OR=2.33, Chi2=3.99 with 1df; p=0.046), histology (OR=1.6, Chi2=0.57 with 1df; p=0.45), or males/females (Chi2=1.81 with 1df; p=0.18). There was no significant difference in RAI dose received for stages 1 versus stages 2/3 (OR=1.37, Chi2=1.50 with 1df, p=0.22).
Discussion
High-dose RAI appropriately correlated with ATA score, and MACIS (MACIS scores ≥7 are considered high-risk for mortality). Interestingly, other factors associated with mortality rate, namely age ≥45 and stage, were not associated with high-dose, however the study may be underpowered for these outcomes.
Overall, substantial patients received high-dose RAI. More judicious use of high-dose RAI may be appropriate given the higher rate of side-effects[2] and small risk of secondary malignancy.