Radioactive iodine (RAI) is widely used in the management of differentiated thyroid cancer (DTC). The impact of the time interval between total thyroidectomy (TT) and RAI administration on disease outcome remains controversial. The objective of the present study was to evaluate the impact of the time interval between TT and RAI.
This study evaluated a cohort of DTC patients who received RAI therapy for whom data on disease status were available. Patients were allocated to one of two groups, according to the time interval between TT and RAI. "Disease-free" was defined as no clinical, imaging, or biochemical evidence of thyroid cancer.
The study included 545 individuals. The TNM stages were: 322 (59.1%) patients in Stage I, 62 (11.4%) in Stage II, 65 (11.9%) in Stage III, and 82 (15.0%) in Stage IV. The median time interval between TT and RAI was six months (P25-75: 3-10 months). Patients were allocated to one of two groups according to RAI timing administration: group A ≤6 months after TT (median 3 months; n = 295), or group B >6 months after TT (median 10.5 months; n = 250). There were no differences for sex, histological type, tumor size, distant metastasis, or RAI dose between the groups (p > 0.1). Patients in group B were older (47.1 vs. 43.1 years; p = 0.02), had less cervical metastasis (73.6% vs. 59.3%; p = 0.002), and were more commonly classified as low ATA risk (48.0% vs. 36.6%; p = 0.027). One year after initial therapy, 59.3% and 65.6% of patients in groups A and B, respectively, were considered disease-free (p = 0.15). Remarkably, the percentage of patients classified as disease-free was similar, even when analyzing a subgroup of high-risk patients (n = 72; 9.5% vs. 10.0%; p = 1.0). These findings did not change after a median of six years of follow-up. Accordingly, further analysis by multiple logistic regression showed that timing of RAI was not associated with persistent disease (relative risk 0.97 [confidence interval 0.80-1.19]).
Timing of RAI does not seem to interfere with the disease outcomes in DTC and can therefore be safely planned while taking into account the health system logistics.