Radioactive iodine therapy dose impact on recurrence and survival in N1 papillary thyroid cancer.

Objective: The objective of this study is to investigate radioactive iodine therapy (RAIT) dose impact on survival and recurrence in patients with papillary thyroid cancer (PTC) with regional lymph node metastasis (N1).

Methods: A retrospective study of PTC patients with N1 disease from 2007 to 2011 at a tertiary academic hospital collected demographics, tumor characteristics, and RAIT treatment dose. RAIT dose was stratified by total dosage less than or greater than 150 mCi. Outcomes included recurrence, immediate RAIT side-effects, and mortality.

Results: A total of 60 N1a and 21 N1b patients were studied with a median follow-up of about 9 years. No statistically significant differences were found between N1a PTC patients who received high-dose vs low-dose RAIT in recurrence rate (6.9% vs 6.7%, P > 0.999) or immediate RAIT side effects (6.9% vs 16.1%, P = 0.426). There were no mortalities in the N1a group. For patients with N1b PTC, there were no differences between high-dose and low-dose RAIT in recurrence rate (41.7% vs 44.4%, P > 0.999), mortality (0% vs 16.7%, P = 0.375), or immediate RAIT side effects (8.3% vs 11.1%, P > 0.999).

Conclusion: Dosages of RAIT ≥ 150 mCi do not appear to provide additional benefit in reducing recurrence compared to doses <150 mCi for N1a or N1b PTC patients. No differences in mortality or immediate RAIT side effects were observed between the two dosing regimens; however, interpretation is limited by low event rates. Large randomized trials are needed for further individualized recommendations regarding optimal RAIT dosage in N1 PTC.