ODP532 Fractionated Radioactive Iodine Therapy in Management of Differentiated Thyroid Cancer

Abstract 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