Relationship between first radioactive iodine administration time and initial response to treatment in patients with papillary thyroid carcinoma

The initial post-surgical radioactive iodine (RAI) therapy for patients with papillary thyroid cancer (PTC) is postponed due to increased demand as well as the limited number of centers to provide RAI therapy. Hence, our aim was to investigate the role of first RAI administration time following thyroidectomy on the number of incomplete response (IR) during the initial follow up, while considering other prognostic factors. Two hundred and thirty-five PTC patients who were admitted to our department for RAI therapy were included in this study. They were allocated into two groups with <3 months (early group) and ≥ 3 months (delayed group) time interval after the first RAI therapy, and the total thyroidectomy. Then, based on the response to RAI therapy, patients were categorized as excellent, biochemical incomplete, structural incomplete, or indeterminate responses (ER, BIR, SIR or IDR, respectively). With respect to age, gender, pathologic variables, RAI dose rate and IR (BIR+SIR) rate, significant differences were found between the two groups. The findings identified that early RAI failed to affect the rate of IR (univariate analysis: HR=1.09, 95%CI: 0.69-1.74, P=0.71; Cox model: HR=0.81, 95%CI: 0.46-1.44, P=0.47). However, Cox multivariate analysis found lymph node status and thyroglobulin level (Lymph node status: HR=2.88, 95%CI: 1.07-7.78, P=0 .04) as independent risk factors for IR during the initial follow up. Therefore, timing of the first post-surgery RAI therapy is not a significant prognosticator of the initial response of patients to therapy.