ODP532 Fractionated Radioactive Iodine Therapy in Management of Differentiated Thyroid Cancer

INTRODUCTION: Management of differentiated thyroid cancer (DTC) requires individualized treatment plans that are tailored to the risk of disease recurrence. Radioactive iodine treatment (RIT) remains a treatment modality that is valuable in certain patients with DTC. The lack of institutional availability and travel bans imposed by the COVID-19 pandemic did not allow a subset of our patients to get intermediate or high-dose RIT. As an alternative, fractionated low-dose RITs given over a short time interval have been used. We aim to study the response to therapy in this patient population. MATERIALS AND METHODS: This retrospective study was performed at a tertiary care hospital in Qatar. Between 2015-2020, patients who completed at least 2 doses of low-dose RIT within 6-12 months with at least one staging visit 3-6 months after their last treatment were included in the study. RESULTS: 69 patients met our inclusion criteria, 30 (43.5%) of whom were males and 39 (56.5%) females. The mean age at diagnosis was 40.7 +/- 9.35 years. Classic papillary thyroid cancer was the predominant histological variant (76.6%). Based on surgical pathology, the initial risk of disease recurrence was high in 24 (34.8%) patients, intermediate in 21 (30.4%) patients, and low in 21 (30.4%) patients. 3 (4.3%) patients did not have complete data for classification. Lymphatic invasion was noted in 16 (23.2%), vascular invasion in 15 (21.7%), positive margins in 30 (43.5%) and extra-nodal invasion in 10 (14.5%) patients. Patients underwent between 2-6 fractionated RITs, with the majority having undergone 2. In the low-risk group, 9 (42.9%) patients had an excellent response to therapy at last follow-up, 3 (14.3%) had the persistent structural disease, and 9 (42.8%) patients had an indeterminate response. In the intermediate-risk group, 7 (33.4%) patients had excellent response, 2 (9.5%) had the biochemically persistent disease, 8 (38.1%) had the structurally persistent disease, and 4 (19%) had an indeterminate response. In the high-risk group, 5 (20.8%) patients had excellent response, 13 (54.2%) had a structurally persistent disease, and 6 (25%) patients had an indeterminate response to therapy. CONCLUSION: A similar response to therapy has been reported in the literature in the low and high-risk recurrence groups, suggesting that additional RIT may not be beneficial. In the intermediate risk of recurrence group, there is a higher percentage of patients with structural evidence of disease compared to what is reported in the literature, suggesting that perhaps a single intermediate or high dose RIT may be more beneficial. Either way, the c urrent management of DTC should be based on dynamic risk assessment to guide the need for further therapies. Presentation: No date and time listed