Abstract and Introduction
Objective: The aim of this study is to investigate whether the number of metastatic lymph nodes (LNs) could be used as a basis in the radioactive iodine (RAI) dose selection for patients with papillary thyroid carcinoma (PTC).
Patients: A total of 595 patients with PTC who received first RAI therapy after total or near-total thyroidectomy and had no evidence of disease in treatment response assessment were retrospectively enroled from five hospitals. The patients were classified into two subgroups based on the number of metastatic LNs (>5). The multivariate Cox-proportional hazard model was performed to identify the significant factors for recurrence prediction in each group as well as all enroled patients.
Results: Overall, 22 (3.7%) out of 595 patients had the recurrent disease during the follow-up period. The number of metastatic LNs (>5) was only a significant factor for recurrence prediction in all enroled patients (odds ratio: 7.834, p < .001). In the subgroup with ≤5 metastatic LNs, the presence of extrathyroidal extension was only associated with recurrence (odds ratio: 7.333, p = .024) in multivariate analysis. RAI dose was significantly associated with recurrence rate in which the patients with high-dose RAI (3.7 GBq or higher) had less incidence of recurrence than those with low-dose RAI (1.11 GBq) in the subgroup with more than five metastatic LNs (odds ratio: 6.533, p = .026).
Conclusions: High-dose RAI (≥3.7 GBq) therapy significantly lowered the recurrence rate in patients with more than five metastatic LNs. Therefore, RAI dose should be determined based on the number of metastatic LNs as well as conventional risk factors.
Radioactive iodine (RAI, I-131) has been used in the treatment of differentiated thyroid cancer (DTC) for decades. According to the 2015 American Thyroid Association (ATA) management guidelines, RAI is usually used for the ablation of remnant thyroid tissues after surgery or therapy of suspected or proven malignant lesions in patients with DTC. In many studies as well as international guidelines, RAI doses have been usually selected in the range of 1.11–7.40 GBq through the assessment of operative findings as well as recurrence risk.[1,2] In practice, the risk stratification suggested in the ATA guidelines or the American Joint Committee on Cancer (AJCC) staging manual has been often used to determine the RAI dose. However, these conventional systems for RAI dose selection are difficult to reflect the physiological characteristics of RAI or the patient’s status after surgery. Thus, it is necessary to find potential factors for determining RAI dose and apply them to clinical practice.
The extent of metastatic lymph nodes (LNs) has been studied as an important predictor of recurrence.[5–7] In particular, DTC patients with more than five metastatic LNs based on the operative findings are classified under the intermediate-risk group regardless of the N category from the AJCC staging manual. The findings of these studies indicated that the number of metastatic LNs is an important factor for predicting recurrence, which could be considered as a potential factor to determine RAI dose.
It is necessary to customise the study design considering the potential factors associated with RAI dose. Therefore, we investigated the association between RAI dose and the prevalence of recurrence based on the number of metastatic LNs and whether the number of metastatic LNs could be used as a basis in the RAI dose selection for patients with papillary thyroid carcinoma (PTC).