Whether the initiating time of radioiodine (RAI) therapy will affect the clinical outcome in differentiated thyroid cancer (DTC) remains controversial. The objective of this study was to evaluate the impact of RAI therapy initiating time in response to initial therapy in low– to intermediate–risk DTC

Selective radioiodine (RAI) therapy contributes to reducing the risk of recurrence and mortality in differentiated thyroid cancer (DTC) patients after thyroidectomy. So far, the optimal time to initiate RAI therapy after surgery remains unclear, and no definite recommendations could be found in current relative guidelines.

The initiating time of RAI varies worldwide and may be affected by personal, social environmental and disease-related factors. Whether the initiating time will affect the clinical outcome of RAI treatment remains uncertain. Few clinical studies have focused on this issue with controversial conclusions.

A total of 235 consecutive patients with low– to intermediate–risk DTC were retrospectively reviewed. According to the time interval between thyroidectomy and RAI therapy, patients were divided into Group 1 (interval < 3 months, n = 187) and Group 2 (interval ≥ three months, n = 48).

Response to RAI therapy was evaluated as excellent, indeterminate, biochemical incomplete or structural incomplete response (ER, IDR, BIR or SIR) with a median follow–up of 780 days. The univariate and multivariate analyses were further conducted to identify factors associated with incomplete response (IR, including BIR and SIR).

Response to initial therapy was significantly different between 2 groups (P < .05), after excluding the impact of other risk factors (age, gender, histological type, the status of T and N, RAI dose, thyrotropin, stimulated thyroglobulin and follow–up time).

A significantly higher IR rate (18.8% vs 4.3%, P = .001) and a lower ER proportion (62.5% vs 78.1%, P = .027) were observed in Group 2. By univariate analysis, both T status and N status stimulated thyroglobulin and time interval were significant risk factors for IR (P < .05). Multivariate analysis demonstrated that the time interval was an independent risk factor for IR (P = .008).

Delayed initial RAI therapy (≥3 months after thyroidectomy) related to incomplete response in low– to intermediate–risk DTC.