Low versus high activity radioiodine remnant ablation for differentiated thyroid carcinoma with gross extrathyroidal extension invading only strap muscles

Oral Oncol. 2018 Sep;84:41-45. doi: 10.1016/j.oraloncology.2018.07.002. Epub 2018 Jul 14.


Objectives: The efficacy of radioiodine remnant ablation (RRA) for patients with differentiated thyroid carcinoma (DTC) with gross extrathyroidal extension (ETE) is well described in observational studies. However, its role in gross ETE invading only strap muscles, T3b category in the newly proposed eighth edition of the TNM staging system, is currently unknown.

Methods: This study retrospectively analyzed 260 DTC patients with ETE invading only strap muscles who underwent thyroidectomy at a tertiary Korean hospital between 1994 and 2005. Cancer-specific survival (CSS) and recurrence-free survival (RFS) in the no RRA (n = 13), low RRA activity (<3.7 GBq, n = 80), and high RRA activity (≥3.7 GBq, n = 167) groups were studied.

Results: No significant differences were observed between low and high activity RRA groups in terms of 10-year CSS (97.3% versus 99.3%; HR 0.23, 95% CI 0.02-2.57; p = .235) and RFS (86.8% versus 88.8%; 0.90, 0.40-2.03; p = .804). In the no RRA group, no patients died of cancer, and only one developed structural recurrence. In Cox regression analyses with inverse probability of treatment weighting adjusted for clinicopathologic risk factors, high activity RRA was not related to recurrence outcomes compared to low activity (HR 0.60, 95% CI 0.26-1.35; p = .214).

Conclusions: Long term oncologic outcomes did not significantly differ between low versus high activity RRA groups, which suggests that low activity RRA might be sufficient in patients with DTC with gross ETE invading only strap muscles. Further studies are needed to clarify the optimal activity of RRA in these patients.

Keywords: Iodine radioisotopes; Neoplasm invasiveness; Prognosis; Radiotherapy; Thyroid cancer.

Publication types

  • Comparative Study

MeSH terms

  • Adenocarcinoma, Follicular / pathology
  • Adenocarcinoma, Follicular / radiotherapy*
  • Adenocarcinoma, Follicular / surgery
  • Adult
  • Aged
  • Carcinoma, Papillary / pathology
  • Carcinoma, Papillary / radiotherapy*
  • Carcinoma, Papillary / surgery
  • Combined Modality Therapy
  • Disease-Free Survival
  • Dose-Response Relationship, Radiation
  • Female
  • Humans
  • Iodine Radioisotopes / therapeutic use*
  • Kaplan-Meier Estimate
  • Male
  • Middle Aged
  • Neck Muscles / pathology*
  • Neoplasm Invasiveness
  • Neoplasm Staging* / standards
  • Propensity Score
  • Proportional Hazards Models
  • Radiotherapy Dosage
  • Recurrence
  • Retrospective Studies
  • Thyroid Neoplasms / pathology
  • Thyroid Neoplasms / radiotherapy*
  • Thyroid Neoplasms / surgery
  • Thyroidectomy
  • Treatment Outcome


  • Iodine Radioisotopes